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ELECTRICAL COMMUNICATION
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A Journal of Progress in the
Telephone. Telegraph and Radio Art
RGN
H. T. Kouruaas, Eprror
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EDITORIAL BOARD
E. A. Brofos
LS RAGIN
G. Deakin E. M. Deloraine P. E. Erikson F, Gill
W. Hatton R. A. Mack H. M. Pease Kenneth E. Stockton C. E. Strong
MONE
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Issued Quarterly by the
tafernatrona! Sfandard Efectric Corporasiont
LOI
67 BROAD STREET, NEW YORK, N.Y., U.S.A.
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Volume XVII January, 1939 Number 3 i
4
(4
PAGE H =
ELECTRICAL COMMUNICATION IN 1988 .......
0.00 eee 205 g
THE APPLICATION OF AUuTOMATIC TICKETING To Step-By-STEP (4
SYSTEMS 0.eee tent e en en bees 230 =
By E. P. G. Wright s
Arrport P.A.B.X. NETWORK ......00 60.0000. cence eens 233 g
By R. T. Ringkjob b
CLARENCE FHUNGERFORD MACKAY ........
0... ce cece cee teen 237
PROCEEDINGS OF THE INTERNATIONAL TELEPHONE CONSULTATIVE =
ComMItTek (C.C.LF.) o. 0... eee cece eee ee 238 HO
TRANSMISSION ‘TESTING APPARATUS FOR 30-10 000 P: s CommuNica- HE
i TION SYSTEMS 2.0.02. eo eee cece eee nee ees 239 iz
E By R. E. Herrick and H. Melling 1g
: EDINBURGH-ABERDEEN CABLE... .. 0... cece cece ce cece eee ees 256 iy
i By H. Birkby ile
' New 3-CHANNEL OPEN-WIRE CARRIER TELEPHONE SYSTEM AND ITS AG
H APPLICATION IN NORWAY ....- 02... ccc cece ee cee nee e cence 263 Fd
: By S. Rynning Ténnesen and A. M. Thornton He
: THEORETICAL RELATIONSHIPS OF DIELECTRIC GUIDES (CYLINDRICAL) Ey
: AND COAXIAL CABLES... 0.00.00 c cece e cece e eee e nen 276 EA
H By A. G. Clavier Hd
Ae VoIce-OPERATED LEVEL CONTROL SYSTEM FOR TELEPHONE NETWorKS 291 Ad
SN: By A. H. Reeves
: HicH FREQUENCY TRANSMISSION LINE NETWORKS ............... 301
E By Andrew Alford
: STANDARDS IN REFRIGERATION AND AIR CONDITIONING ........-...4. 311
By Glenn Muffly E
RECENT "TELECOMMUNICATION DEVELOPMENTS OF INTEREST ........ 314 :
HS
XI On STITT UCC CHTAHONYRATATOGAUUEACAEDAIIESUCUGESEUGUEUIEEGEEITOCUANUBSYOUGUOSUSDEAUIGUSIEFOORTES =
= NOWOO RTS WM ORMOVM Ora Owxi@rWMCwronxOr©|FeS
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Entrance to the French P.T.T. 30 kW Eiffel Tower Television Station.
Electrical Communication in 1938
Eprror’s Note.—This Review, while international in scope, is. not intended to cover. comprehensively
communication activities in all countries of the World—the subject is far too vast. Emphasis, in general, is placed
on European developments and activities in which Companies in the International Telephone and Telegraph
Group, to some extent at least, participated. It is believed, nevertheless, that the following pages give a fairly
inclusive indication of the advances achieved in various phases of the communication art and its allied applica-
tions during the year 1938.
GENERAL present time, a manual method or, unless
HE telephone, affording as it does a automatic ticketing is available, an incompletely
means of instantaneous exchange of automatic method. In limited areas where each
ideas regardless of distance or country, subscriber is given a message register, where
makes the peoples of the world neighbours in the distances are short, and where all tariffs
a real sense. Technically, it is possible to-day are multiples of a common unit, multiple
to interconnect any two distantly located sub- metering on a timed basis may be used as a
scribers ; and a stage has been reached where substitute for automatic ticketing, but obviously
the development of national and international such a system lacks the flexibility and general
telephony is dependent mainly on economic utility of automatic ticketing. It is becoming
considerations and rapidly obtainable sub- increasingly apparent, moreover, that no method
scribers’ connections. In the solution of this of long distance operation. can be considered
present day phase of the problem, the evolution completely automatic from the viewpoint of the
of the machine switching art doubtless will play telephone subscriber (or from that of the
a leading part, as will also economy in providing Administration or Operating Company), unless
the necessary allied transmission facilities. all the usual requirements for local machine
Despite many outstanding developments in switching operation are met, and the equivalent
machine switching, long distance transmission of the information afforded by the toll ticket,
and international radio communication, it is an employed in manual operation, is supplied. In
interesting fact that, from the viewpoint of the the contrary case, toll service is obviously
telephone subscriber’s initiation of a call, only inferior to local service, judged by automatic
three fundamental stages have been generally standards.
introduced since the birth of the telephone in Considered from the viewpoint.of Administra-
the 1870's : tions or Operating Companies, notable
(1) Local battery manual service, developments—such as have been attained in
(2) Common battery manual service, and machine switching by automatic toll ticketing
(3) Automatic telephone service (as yet as well as national dialling ; in toll transmission
applied only partially to toll operation). by broad band (coaxial cable) or multi-channel,
If the average lay subscriber were asked multi-conductor cable systems ; and in radio,
whether automatic telephony from his viewpoint by ultra-short wave multi-channel systems—
represents a completed development, he afford means for furnishing a secret, rapid and
probably would answer affirmatively. In truly comprehensive automatic service to sub-
machine switching areas it is, however, ordinarily scribers, not only on local calls but also on toll
necessary for the subscriber to employ a different or long distance calls. Furthermore, the newer
method in placing local calls as compared with machine switching. and transmission systems
toll calls. The former in many cases represents are inherently more economical than the older
a wholly automatic method; the latter, at the ones. Thus, with facilities available for furnish-
205
ELECTRICAL COMMUNICATION
ing greatly improved systems at reasonable Dialling, the first practical demonstration on
rates, conditions, at least in many countries, March 3ist, 1931, of Micro-ray Radio across the
would seem to be ripe for an accelerated develop- English Channel, Single Side-Band Short
ment of the long distance and toll services Wave Radio and Ultra-short-wave Multi-
comparable with the achievements in local channel Radio (Belfast, Ireland—Stranraer,
networks. Scotland), as well as the provision of the first
The introduction of automatic toll ticketing 12-channel carrier-on-cable system placed in
recalls to mind discussions that arose in the commercial service and the 30 kW Eiffel Tower
early days of automatic telephony as to the Television ‘Transmitter, the most powerful at
merits and subscriber-appeal of fully automatic present in operation.*
versus manual telephony. To-day, not only
in local, but also in toll operation, subscribers’ SUBSCRIBERS’ EQUIPMENT
reaction has proved that they, as well as Operat- Subscriber set developments have been
ing organizations, prefer purely automatic directed towards two main objects: (1) higher
working. Obviously the same considerations grade of transmission; (2) reduction in main-
apply ‘in favour of systenis including automatic tenance cost in the field by (a) improved protec-
toll ticketing as compared with other methods : tion of the components against the effects of
(1) semi-automatic working with manual toll dust and humidity, and (b) provision for greater
ticketing; and (2) fully automatic working ease of maintenance.
with time and zone metering, capable, however, Higher transmission quality, to which much
of furnishing only an integrated record of charges attention has been directed during the last years,
rather than essential detailed data on individual holds first rank in the development of the
calls. subscriber set components. General recogni-
The telephone world is indebted to the tion, moreover, is being given to the fact that
progressiveness and foresight of the Belgian judgment based on results obtained by voice
“Régie des Télégraphes et des Téléphones” and ear testing teams may lead to very erroneous
for having been the first to try out and introduce appreciation of the efficiency of subscriber sets.
automatic toll ticketing ; and, hence, from the Testing methods for the finished products,
viewpoint of the subscriber’s initiation of toll accordingly, have been modified soas to eliminate
calls inaugurating, in the year 1937 and mote the human factor, and to-day the approach is
particularly in 1938, what may be termed the by the most up-to-date laboratory technique.’
fourth stage in telephone advancement, making 1938 saw the completion by Standard
it possible for the subscriber to employ precisely Telephones and Cables, London, of the develop-
the same methods and achieve the same results ment of a telephone handset receiver of
in the toll and long distance, as well as in the substantially improved transmission quality for
local field,—wholly automatically. use by the British Post Office. Field trials of
Automatic Ticketing as a desideratum is not receivers with similar features gave very satis-
new; its reduction to practice, however, was factory results, and the new receivers are now
long regarded as impracticable. The fact being produced in quantity. A correspondingly
that it was developed by two organizations improved head receiver is also being made.
in the group of companies contributing Similarly, the Bell Telephone Manufacturing
regularly to Electrical Communication—Bell Company, Antwerp, is about to place on the
Telephone Manufacturing Company, Antwerp, market an improved capsule type receiver for
and Les Laboratoires, Le Matériel Télé-
use in its standard handset. ‘This capsule
phonique, Paris—seems appropriate inasmuch receiver also is of higher quality than the present
as the International Telephone and Telegraph one, whilst retaining the same efficiency.
Group of Companies is the largest single Results, in all these cases, have been achieved
supplier of automatic telephone equipment by the application of electrical network theory
outside of the U.S.A. Other outstanding to the acoustic design, and by the use of the most
contributions of the International System, it is
interesting to note in passing, include National * See references 1 to 6 at the end of this Review.
ELECTRICAL COMMUNICATION IN 1938 207
suitable magnetic materials selected from the of automatic ticketing in 1938 greatly surpassed
wide range now available. that of 1937. At the end of the latter year,
Considerable development work has been 14 650 lines equipped with this facility were on
done by Standard Telephones and Cables order or installed; the figure at the end of
towards producing a telephone transmitter with 1938 reached 134 240 lines. This remarkable
less frequency distortion and less non-linear increase is due mainly to the decision of the
distortion ; important contributions along these Belgian Régie to introduce automatic ticketing
lines have been made by British Post Office in the Brussels network: all multi-fee connec-
Researches (unpublished). Development work tions, outgoing from Rotary exchanges installed
continues. in the city of Brussels, will be controlled by
printer registers producing tickets containing
ROTARY AUTOMATIC SYSTEM
the number of the calling party, the number of
The year 1938 witnessed a remarkable
the called party, the duration of the conversa-
expansion of Rotary equipment, the Rotary
tion in minutes, the basic tariff, the time of day
automatic system now being installed in 960
and the date. The plans involve the progressive
exchanges and 42 countries. The total number
automatization of the whole of Belgium and
of lines installed or on order at the end of 1938
were adopted by the Belgian Régie after the
was 2 250000, a net increase for the year of
successful field trial of automatic ticketing
125 000 lines.
between Bruges.and Blankenberghe.
The largest Rotary network—the Paris City
Brussels will be the first capital city to adopt
area—was converted in 1938 to 100 per cent.
automatic subscriber-to-subscriber dialling for
automatic operation. This conversion was
toll and rural services, coupled with a printed
handled by Le Matériel Téléphonique, Paris.
record of each connection, providing all the
Two Rotary exchanges (5 400 lines) also were
data formerly obtained by manual ticketing
placed in service in the Paris Suburban area,
methods.
bringing the percentage of automatic operation
A further step in the application of automatic
to. 70%. There still remain six offices (22 200
ticketing systems was achieved with the cut-
lines) to be cut into service, all of which are
over of a new 7-D exchange in Ostend, Belgium,
under construction, to complete this stage of
on June 17th. In addition to providing a printed
the conversion to automatic service.
record of outgoing multi-fee connections, the
Transformation of the Paris Regional area to
Ostend equipment includes number identifica-
automatic operation was started in 1938, Three
tion equipment for outgoing no-delay toll
offices (6 200 lines) of the “‘center” type and one
connections handled manually. This number
satellite (50 lines) were placed in service, while
identification equipment displays, in front of the
one “‘center’’ type (800 lines), three ‘‘sub-
toll operator, the calling party number which is
center” type (1 900 lines) and six satellite (590
obtained from the identification equipment
lines) offices are in process of construction.
associated with automatic ticketing. Special
Orders received for the new 7-A2 type Rotary
trains of selectors, formerly used for checking
equipment included Belgium, Brazil, New
the number of the calling subscriber, are there-
Zealand, Norway, Peru, Rumania, Switzerland
fore not required.
and other countries.
The Hungarian Telephone Administration
The 7-D type Rotary system, designed
also has decided to introduce automatic toll
primarily for small towns, continues to find
service in Hungary. Automatic ticketing equip-
increasing application.
ment will be utilized, involving Budapest,
Further development of the Oslo suburban
Papa and Miskolc.
and regional networks took place with the cut-
In accordance with the policy of the Japanese
over of the 2600 line Stabekk exchange and
Ministry of Communications, the use of
thirteen exchanges with 4910 lines in the
automatic equipment not requiring the inter-
Drammen area.
vention of an operator is being extended.
AUTOMATIC TICKETING Equipment now in process of manufacture
Progress in the development and application provides for the calling subscriber first dialling
208 ELECTRICAL COMMUNICATION
the toll number and then that of the distant for public service, and of these 346 were of the
party; also for recording automatically the rural unit type. The elimination of the smaller
calling and called subscriber’s numbers, the and older manual exchanges also progressed
duration of a conversation, the date, etc. considerably, and the year saw the completion
of the two-thousandth small unit automatic
NATIONAL DIALLING exchange.
In Holland, Rotary equipment in The Hague Standard Telephones and Cables, Limited,
is being arranged to provide national dialling completed a large programme of automatic
facilities. These exchanges were amongst the equipment during the year, including the
first to be provided with Rotary equipment and equipment for the exchanges serving the large
were originally designed for semi-automatic suburban areas of Finchley and Ealing, as well
operation with automatic distribution of calls as Albert Dock, the exchange serving its North
to operators, who completed connections by Woolwich factory. Over 1000 unit type
means of key sets on which the required number equipments also were supplied for rural service.
was depressed. For the Commonwealth of Australia, over
The semi-automatic equipment was later 11000 lines of equipment are in process of
converted to full automatic; the original manufacture, including the central office equip-
switches are still in service. ‘The introduction ment for Fremantle and for Redfern, the
of national dialling facilities is accomplished by exchange serving the new factory of Standard
the addition of new traffic paths and the segrega- Telephones and Cables (Pty.), Limited,
tion of outgoing automatic toll calls from local Australia. Step-by-step equipment also was
calls. Provision for the introduction of auto- supplied for the central office and two satellites
matic ticketing of outgoing toll calls is made for in Colombo, Ceylon.
subscribers who request details of their The development of the telephone networks
telephone account. of the United River Plate Telephone Company,
The complete automatization of The Hague Limited (Argentina), and of the Chile Telephone
zone or district also is progressing. Rotary Company, both of which are comprised in the
equipment will be installed in the important International Telephone group of companies,
towns of Leiden and Delft. necessitated provision during the year of over
In Zurich, Switzerland, a new full automatic 30 000 lines of equipment for new exchanges
national toll exchange was cut-over on May Ist and other purposes.
and an extension is in process of manufacture. During 1938, 2080 French villages were
The equipment now handles the full automatic equipped with semi-automatic rural switch-
outgoing toll traffic from the entire Zurich boards constructed by Compagnie des
network, comprising 65 exchanges, to five other Téléphones Thomson-Houston, and operating
Swiss networks, including 80 exchanges. When on R-6 system principles. At the end of the
the extension is completed, connection will be year, there had been installed for the French
made to 11 different networks. P.T.T. 2337700 lines of R-6 equipment in
The first installation in France of ‘‘subscriber- 6 673 offices.
to-subscriber toll dialling’? was completed by
CROSSBAR SWITCHING SYSTEM
Compagnie des T’éléphones Thomson-Houston
during 1988 between the two large step-by- Following the successful trial of a Crossbar
step areas of Rouen and Le Havre. Switching System installation in Brooklyn, New
York City, the first full sized installation of this
STEP-BY-STEP system was placed in service during July in the
Grand Central area of New York City.
Rapid progress has been made in Great
The Crossbar System, developed by the Beil
Britain in the automatic conversion programme,
Telephone Laboratories, Inc., replaces the
particularly with regard to the special plans for
Panel System for new installations.
rural services.
During the year ended September 30th, no COMMUNICATION SYSTEMS—GENERAL
fewer than 393 automatic exchanges were opened The successful operation of 12-channel
ELECTRICAL COMMUNICATION IN 1938 209
carrier-on-cable systems in Great Britain, where during December. Furthermore, a large group
they have been used on a large scale, has of circuits between London and Manchester
aroused widespread interest, and many will be brought into service towards the middle
Administrations are considering such systems of 1939. Between Manchester and Leeds,
in their Toll Planning. A stage has now been 48 circuits, with terminal and repeater equip-
reached where the C.C.I.F. is considering the ment built to a later design, are now undergoing
standardization of some of the more important field trials.
features. Coaxial cable systems, too, are The 12-channel multi-conductor system in
becoming of sufficient importance for some Great Britain also was extended considerably
preliminary discussions leading to standardiza- during the year. The laying of 1265 km of
tion of fundamental operating requirements by cable was completed, and a further 1820 km
the C.C.LF. is under construction. Over 3760 km of
Echo suppressors for voice frequency circuits 12-channel cable are now completed or under
have normally been applied at an intermediate construction, representing a route length of
point. The application of carrier systems to over 1 880 km.
cables necessitates the location of the echo In addition to underground cable schemes, 12-
suppressors at the terminals ; the new problems channel carrier telephone equipment has been
thus created have been actively pursued and new successfully applied to submarine cables, linking
types of suppressors evolved and given final trials. Great Britain with Holland and with Ireland.
The progress of television during the year Paralleling these installations of important
necessitated thorough study of associated trans- new types of cables, normal loaded trunk cables
mission systems. Much was accomplished in were completed or under construction in
this allied transmission field. Great Britain with a total length of 3713 km
The operation of toll circuit terminal and as compared with 3 225 km in 1937.
repeater equipments from power mains without A 12-channel carrier cable from Antwerp,
the use of rotating machinery continues to Belgium, to Roosendaal, Holland, has been
arouse considerable interest. Improvements manufactured and the installation is scheduled
in dry rectifiers, electrolytic condensers, voltage for completion in March, 1939. The plan is to ex-
regulating devices and emergency automatically tend these circuits to Rotterdam, Holland, where
starting prime-mover plant enable high efficiency the necessary cables between Roosendaal and
equipments to be realized. Rotterdam already exist. Multi-channel carrier
Progress was made during the year in the long- cables also have been laid in Holland between
distance dialling art. Applications of agreed Goes and Roosendaal, Eindhoven and Hertogen-
principles are now in hand in various countries. bosch, Utrecht and Amsterdam, Deventer and
In the field of transmission testing apparatus, Leeuwarden, making in all a total of 400 km
much was accomplished in the provision of of route length over which these modern cables
simplified equipment with increased frequency are available. Later extensions to this system,
ranges and direct reading facilities. Progress covering a further 400 km of route length, have
also was made with the operation of this type been planned.
of equipment from A.C. mains. In the above countries, the multi-channel
carrier cables are designed solely for carrier
PROGRESS IN WIRE TRANSMISSION circuit operation; in Rumania, however, a
SYSTEMS combined 12-channel and normally loaded
The 4-core coaxial cable network in Great 2-wire cable has been completed between
Britain was extended ; 218 km were completed Bucharest and Ploesti (60 km), and an extension
in 1938, whilst a further 132 km are under of this cable to Brasov (a further 110 km) is
construction. Thus 550 km route length be- proceeding.
tween London and Newcastle is nearing In France, the Paris—Bordeaux coaxial cable
completion. Between London and Birmingham has been proceeded with, and work was com-
40 coaxial circuits have been in regular service menced on the French section of a London-
since last summer, and 40 more were added Paris 12-channel cable system. The submarine
210 ELECTRICAL COMMUNICATION
cable portion of this installation will be in oscillators and filters increased further during
essentially of the same design as the land cables. the year. Employment of these crystals has now
In Switzerland, a number of cable circuits become a recognized technique in high stability
has been equipped with single channel carrier oscillators, as well as in bandpass filters for
telephone systems. frequencies of the order of 60 to 120 kc/s in
A project is in course of realization for cases where characteristics appreciably more
operation on the (Anglo-Belgian) St. Margaret— precise than those obtainable with condenser
La Panne submarine cable of thirty systems and inductance networks are required.
each comprising one voice and two carrier In consequence, methods of production and
telephone circuits. of measurement of quartz plates have been
In other European countries, progress further improved, and quartz plates are now
continued. Long-distance telephone networks produced on a commercial manufacturing basis.
were extended in accordance with plans which It is fully expected that this comparatively new
have been followed during the past few years, electrical element will play an important part
employing loaded cable systems and carrier in the design of future systems.
on open-wire lines.
The Japanese telephone network now includes C.C.LF.
several thousand kilometres of non-loaded cable. The recommendations passed by the
A notable accomplishment is the Tokyo to Technical Commission meetings at Oslo, in
Hoten (Mukden) line extending across the June 1938, showed that notable progress has
Chosen Strait (270 km) to Chosen (Korea), been made by the C.C.I.F., particularly along
and thence to Hoten, Manchukuo. The multi- the lines of (a) the European Toll Switching
core submarine carrier cable (paper insulated) Plan ; (6) Guiding Principles for Long Distance
contains fourteen pairs of 2.0 mm wire divided Dialling; and (c) Guiding Principles for the
into two groups of seven pairs each, each group application of Carrier-on-Cable Systems.
working in opposite directions. Special shield- The sub-committee on the European Switch-
ing is provided between each group. ‘T'wo of ing Plan held a number of meetings; and,
the three repeater stations, equipped with based on examination of data supplied by
carrier repeaters, are situated on islands in the numerous Administrations and Operating
Strait. Highly successful results have been Companies, the Oslo meeting recommended
achieved and greater use of this type of cable certain revisions and expansions of the general
is anticipated for submarine application. instructions for the European Switching Plan.
Open-wire carrier equipment of new design At this same meeting, general agreement was
was provided for operation in Norway, Finland, arrived at on a number of points fundamental to
Russia, Rumania, Jugoslavia, Czechoslovakia, the international application of toll dialling.
Bulgaria, Palestine, India, Malaya, South Africa, Likewise, agreement was reached on certain
Australia and New Zealand. important points relating to application in the
Mention should be made of an important European network of the latest multi-channel,
open-wire carrier system which is to be installed multi-conductor carrier-on-cable art.
in Australia between Sydney and Melbourne In order to expedite the handling of urgent
(approximately 1000 km), a 12-channel carrier questions involving the rating of telephone
system for this route being now. in process of circuits and the application of carrier technique
manufacture. to cable circuits, sub-committees were appointed
Voice Frequency telegraph systems continue to hold meetings at intervals between general
to play a major part in the development of Commission and Plenary Assemblies. Thus,
telegraph networks. Equipment of this type has the work of various Administrations and
been provided for the realization of numerous Operating Companies can be closely followed
projects. up and co-ordinated.
Two of the above mentioned sub-committees
CRYSTALS held meetings in London during December,
Applications of piezo-electric quartz crystals 1938. The sub-committee on the rating of
ELECTRICAL COMMUNICATION IN 1938 211
telephone circuits met from December 5th—
10th inclusive, and outlined a _ detailed
programme of tests-to be made by the SFERT
laboratories in order to learn whether the
correlation between articulation plus received
volume and repetition rate might be utilized
for the determination of rating without resort
in all cases to the repetition rate method.
) 20-30 «kw
Repetition rate is still considered the best
13-1%o
criterion for determining the performance of a
telephone connection; the difficulty and cost
involved in obtaining rating by this method,
100- 500 Kw
however, make it highly desirable to develop a
more readily applicable method such as the C44 Vo 30-100Kw
one now under study. The sub-committee 18-1%
on carrier-on-cable met from December 12th—
17th inclusive ; basic principles for the applica-
tion of carrier on coaxial cable were discussed
and a number of fundamental points settled. Distribution of Power Rating in a Group of 160 Medium
Thus it should be possible to maintain develop- and Long Wave Broadcasting Stations of 5 kW rating and
upward in the European Region.
ment work in progress in various countries
along lines sufficiently similar to permit of
ultimately evolving systems suitable for universal modulating amplifiers, or low power modulation
application on the continent of Europe. with separate amplifiers for different com-
The Ist and 2nd C.R.’s completed a revision ponents of the modulated wave, as in the
of the ‘Recommendations’ concerning the Doherty circuit.
protection of cables against electrolysis and Outside the U.S.A., the first high power
interference. These new recommendations Doherty type station is the 50 kW Broadcasting
were submitted to all Administrations and Station of the Municipality of Buenos Aires,
Operating Companies for a postal vote and, if placed in service in the spring of 1938.
passed, they will come into force as of January In Europe, medium wave broadcasting is now
Ist, 1939. established on the basis of a power of approxi-
A special sub-committee was appointed to mately 100 kW for nearly 25% of all main
study means of providing a more rapid inter- stations. A number of such high power
national service. Questions on this subject are stations are in course of construction, including
now under active consideration by this com- a 100 kW at Start Point, England, a 100 kW
mittee and by the various Administrations and in Sweden, two 100 kW in Norway, a 120 kW
Operating Companies adherent to the C.C.L.F. in Lithuania and a 120 kW in Ankara, Turkey.
Meeting a demand for still higher power
RADIO BROADCASTING (INCLUDING involves a problem which will have to be
SPEECH INPUT EQUIPMENT) settled at the forthcoming European Broadcast-
While the technical development of broad- ing Conference to be held in Switzerland in the
casting systems has by no means reached spring of 1939. At present, by international
finality, progress in 1938, as in 1937, was agreement, no European station is normally
characterized mainly by the continued exploita- entitled to use more than 120 kW. In the
tion of existing technique. Outstanding, United States the maximum station power
probably, are the emphasis laid on high over- normally licensed has so far been restricted to
all efficiency and the adoption in all new medium 50 kW, but here also there is a definite demand
wave transmitters of one or other of the high for the allocation of higher power, a rating of
efficiency modulation systems; for example, 500 kW being advocated as not unreasonable.
the use of high-power final stage Class B Recent developments in quartz crystal
242 ELECTRICAL COMMUNICATION
technique have resulted in the installation of required frequency, while provision is also being
independent crystal drives at B.B.C. stations made for the synchronous operation of up to
sharing a common wavelength. This system four transmitters from the same crystal.
has replaced the distribution over telephone The new Rome station, comprising two
circuits of driving tone generated by a tuning 100 kW and one 50 kW transmitters, is nearing
fork oscillator at a master station, and: has completion. One of the 100 kW short wave
resulted in improved reception from the broadcasters (installed by Fabbrica Apparec-
synchronized transmitters. Each crystal oscil- chiature per Comunicazione Elettriche for the
lator has a frequency stability of the order of E.I.A.R.) was inaugurated October 31st, 1938.
one part in 107 over a period of 24 hours. In In the United States the Columbia network
order to maintain beats between the carrier has made special provision for short wave
waves of the respective stations at a very low broadcasting to Europe, and the very successful
frequency, inter-station frequency checks are relaying in European countries of programmes
made once or twice daily so that any necessary thus transmitted is an established feature.
adjustment can be made. Expansion of the Indian broadcasting system
The use of anti-fading aerials is now an has made good progress; there are now eight
accepted feature of all new medium wave short wave regional stations in regular operation,
broadcasting stations. Such aerials may be of rated at 5kW to 10 kW. In addition, a central
either the high mast type with no top-capacity station at Delhi radiates a news service and
loading, or of the type with a rather shorter mast general interest items which are relayed through
combined with a capacity crown connected the regional stations. The furnishing of a
to the top of the mast through an inductive broadcasting system in India is attended with
reactance. In all cases the height of the current peculiar difficulties, not only because of the
loop above ground is about 0.25A to 0.34. The enormous territory to be covered and economic
actual height of the radiating element is not considerations, but also because of the problem
less than approximately 0.4A, corresponding to of providing suitable programme material for
an electrical length of 0.54 to 0.57%. a country which has twelve distinct main
An American development, which appears languages and some four hundred dialects.
to be assuming some importance, is the use of Since, in country districts, it is quite out of the
aerial arrays for medium-wave broadcasting, question for each family to acquire its own
designed to control the shape of the horizontal receiver—even the cheapest receiver is beyond
diagram in order to supply increased field the means of the average native and, in any case,
strengths in certain areas and to avoid creating power supplies and battery charging equip-
unnecessarily strong field strengths in others. ments are very scarce—a scheme of “communal”
Typical examples are the three-element arrays village listening has been instituted. Under this
at WOR (Carteret, N.J.), and at WLW (Mason, system a village is supplied with a battery
Cincinnati, Ohio). operated loud speaking receiver equipment,
Short-wave long distance broadcasting permanently tuned, and switched on at set
continues to grow in importance, and practically hours by means of clock-switches. While the
every European country either has installed or cost of such an equipment is borne by the local
is planning to install equipment for broad- administration, the actual supply and main-
casting to its nationals on other continents. tenance devolves on the broadcasting authorities
The B.B.C. is adding further high-power themselves. ‘The latter are thus in the unusual
transmitters to its ““Empire”’ station at Daventry, position of being directly responsible for both
where five new aerials are to be erected, two to transmission and reception.
serve Central America, and the other three The provision of local broadcasting services
South America. A central drive room is being by countries situated in the tropical zones has
built to house the crystal drive equipment for hitherto been restricted by the lack of a suitable
the whole station. The output channels band of wavelengths. The medium waveband
provided will enable any number of transmitters used so effectively in the temperate zones is
up to twelve to be fed independently with any useless in tropical regions owing to the high
ELECTRICAL COMMUNICATION IN 1938 213
static noise level, while the short wavelength Broadcasting House, Glasgow, Scotland, was
broadcasting bands were primarily intended for opened in November, with ten studios, a control
long distance working and suffer from skip- room and offices. The largest studio has a
distance effect at a comparatively short radius volume of 182 000 cu. ft. and will accommodate
from the transmitter. In view of these an orchestra of 100 players.
difficulties, the Cairo. Telecommunication In Switzerland new studios are being put
Conferences in 1938 made provision for local into service at Zurich and Lugano, employing
broadcasting in the tropical zones in the negative feed-back amplifiers of the type
frequency bands between 2300 kc/s to 2 500 adopted by the I.N.R. in Brussels and by
ke/s (130.4 m-120 m), 3 300 ke/s to 3 500 ke/s R.A.V.A.G. in Vienna.
(90.91 m-85.71 m), and 4770 kc/s to 4 965 ke/s In Denmark a new broadcasting house will
(62.89 m-60.42 m). By the use of these be erected in Copenhagen containing 20
‘“ntermediate” bands it is hoped to avoid both studios, the largest of which will be of 280 000
the high static level of the medium waves and the cu. ft. capacity, and accommodating an orchestra
skip-distance limitation of the short waves. of 100 and a chorus of 110 singers. The
It is yet too early to estimate the effect of this equipment will be supplied by Standard Electric
change in promoting local broadcasting in A/S, Copenhagen.
tropical regions.
Development in studio and speech input TELEVISION
equipment was concentrated on providing mains- Great Britain is the only country in the world
operated equipment in a manner such that each having a regular commercial television service :
unit is self-contained and furnished with its the British. Broadcasting Corporation is furnish-
own power transformers, rectifier and smoothing ing a four-hour daily service, including out-of-
equipment. The tendency is to rely on prime- door events. In France, vision broadcasting,
mover equipment only in cases of mains failure. both studio and film, is now taking place two
In the acoustical treatment of studios, it hours daily, five days a week, from the Eiffel
might almost be said that two schools of thought Tower transmitter.
have arisen. One holds that the acoustics of a Television Standards.—Progress towards the
studio are best controlled by geometrical adoption of common standards for television
factors, i.e., the shape and size of the room, services can be recorded for the year 1938.
and the provision of surfaces at suitable angles. Great Britain, France and Germany all
The other school concentrates on the nature adopted positive modulation and uniformity
and absorbent power of the surfaces, rather than of synchronizing signals. The number of lines
on the geometrical disposition. Excellent used, however, differs: 405 in Great Britain ;
results have been obtained by both methods. 455 in France; and 441 in Germany. _ Italy is
The new centralized studio system of the believed to be following the German practice.
Belgian Institut National de Radiodiffusion No definite standards have so far been adopted
at Brussels, supplied by the Bell Telephone in America. The last R.M.A. recommendations
Manufacturing Company, Antwerp, was cut call, contrary to the European standards, for
into service during 1938. This is a typical negative modulation; also for spacing of the
example of European practice, and provides vision and sound carriers of approximately
no less than seventeen separate studios, a number 4.5 Mc as soon as single side-band operation
of which may participate simultaneously in the of the vision transmitter is practicable.
broadcasting of a play. This use of a number of Wire Transmission—Thus far, with the
studios for a single programme item may be exception of the 180 line visio-telephone service
contrasted with the general practice in the involving Berlin, Munich, Nuremberg and
United States of employing, whenever possible, Hamburg, Germany, no regular long distance
only one studio per item. From the technical transmission of television images has been
viewpoint, the specialized use of studios is realized.
intimately bound up with the previously In the U.S.A., following the completion of
mentioned question of studio acoustics. satisfactory telephone and television tests over
214 ELECTRICAL COMMUNICATION
the New York—Philadelphia coaxial cable transmission over distances of a few hundred
arranged for one megacycle transmission, addi- kilometres. No definite plans have been
tional equipment was added to permit trans- formulated and it is not felt that this problem
mission up to two megacycles. Tests using this will be solved in the near future.
frequency band are now in progress. Scanning Systems.—Iconoscopes are used
In Great Britain, experiments are being almost exclusively for vision transmissions.
conducted on the transmission of visual signals For film scanning, Fernseh employ mechanical
over ordinary telephone lines. To date, success- film scanning giving very good images and also
ful pictures have. been received over distances a dissector tube using the Farnsworth principle
of 2-3 miles, and it is hoped to extend this which, in the case of films, gives images com-
range to four miles or more. Thus many parable with the iconoscope images.
important sources of programmes may be Television Transmitters
——In France, the Eiffel
linked to the balanced-pair television cable Tower vision transmitter, ordered by the
encircling Central London. Considerable work French P.T.T. from Le Matériel Téléphonique,
also has been done towards the realization of was inaugurated by the P.T.T. Minister on
long distance television transmission over coaxial April 8th. The output power was raised to
cables. 30 kW and a new antenna placed in service at the
An order for a television terminal equipment end of 1938. Good reception has been reported
was received by Societd Italiana Reti Telefoniche all round Paris and also on the south coast of
Interurbane for the Rome Television Station. England. The quality of the pictures compares
Radio Links——Some consideration has been favourably with those from other transmitters
given to the use of radio links for television in operation.
Exffel Tower 30 RW Television Transmitter installed for the French P.T.T. by Le Matériel Téléphonique,
Paris.
ELECTRICAL COMMUNICATION IN 1938 215
The Eiffel Tower transmitter is completely
A.C. operated. Good stability is obtained by
the use of inverted amplifiers, and phase shift
is minimized by proper dimensioning of the
circuits of the last stage. The response is
flat within a few db. and the overall time
delay is constant within a few hundred micro-
seconds.
In Germany, a transmitter adapted to the
new German standard is under test.
During the Berlin Radio Exhibition in
August, all. demonstrations were based on the
new standard but were made by local wire
connections or from a 100-watt transmitter.
In Italy, a 2 kW television transmitter was
ordered for Rome. Fernseh will supply the
scanning equipment.
Television Receivers——The 1938 Berlin,
London and Paris Radio Exhibitions, held in
August and September, showed important
effort towards the commercialization of tele-
vision receivers, particularly in the case of the
London Exhibition.
At the Berlin Television Exhibition, Fernseh,
Telefunken, Tekade, Loewe and Lorenz showed
various home-type models of television receivers
and also projection-type receivers for large
audiences. Of the receivers in operation, the
majority were made by Fernseh.
Fernseh demonstrated a projection type
receiver giving very good 10’ x 12’ images.
Telefunken showed projection type receivers Kolster-Brandes No. 790 Television and All-Wave
giving approximately 3’ x 4’ images. A Lorenz Receiver.
projection type receiver producing a smaller
image also was demonstrated.
At the London Radio Exhibition, at least quality was very uniform, the receivers demon-
twenty radio set manufacturers demonstrated strated by Kolster-Brandes being amongst the
television receivers at their stands. About 100 best.
television receivers were in operation. Kolster- Projection type home receivers giving images
Brandes, Limited, demonstrated three types: between 18” x 15” and 24” -x 20” were also
a console receiver (No. 780) with twenty valves demonstrated by Baird, Marconi, Philips and
producinga picture 10” x 8” for direct viewing ; Scophony. The image of the Baird receiver
a similar receiver (No. 790) but more sensitive, was black and white, while the images of the
incorporating an all-wave radio receiver, and other projection type receivers were of a light
arranged for viewing in a mirror type cabinet greenish-yellow colour.
utilizing 26 valves in all; and a table type At the Paris Radio Exhibition, about fourteen
receiver (No. 800), employing 17 valves and television receivers were demonstrated by five
providing a picture 7” x 6”. firms, two of them only offering receivers for
Most of the receivers in operation at the sale.
London exhibition were of the direct viewing During 1938, the trend in television receiver
type, only a few using mirror viewing. The construction was towards the reduction of the
ELECTRICAL COMMUNICATION
size of the cabinet with respect to the image total of sixteen aerials, and will provide for a
dimensions. This was accomplished mainly total of twelve channels during times of favour-
by decreasing the length of the cathode-ray able radio conditions. The German equipment
tubes. provides for the initial installation of a six-
The number of valves in television receivers unit M.U.S.A., with the possibility of increasing
was reduced appreciably. Most- receivers the number to twelve units at a later date.
utilized between thirteen and twenty. Apart from its commercial utility, the
The majority of the receivers used magnetic M.U.S.A. system is of value in the study of
type cathode-ray tubes; an important propor- propagation conditions. The Bell Telephone
tion, however, still employ electrostatic type Laboratories, Inc., report, for example, that
tubes. considerable lateral change in the angle of
The prices of the television receivers shown arrival of a signal occurs on occasion—some-
at the London exhibition ranged between times as much as fifty degrees off the great
21 guineas for 4” x 33” direct viewing types and circle bearing of the transmitting station.
220 guineas for the 20” x 24” projection type. On June 2\st, direct commercial telephone
It is estimated that the number of television service was established between Chile and
receivers in service in England at the time of Japan through the co-operation of the Japanese
opening of the London exhibition was between Government and the Compania Internacional
8000 and 10000, and that at least the same de Radio de Chile, an associated company of
quantity was sold during the exhibition. the International Telephone and Telegraph
Corporation. New diamond loop antennae
COMMERCIAL RADIO were constructed in Santiago, Chile, pointed
During the past few years much effort has on Tokyo, and the powers of the transmitters
been directed towards the application of single in the two cities were raised to 8 kW and 10 kW,
side-band working to short wave transoceanic respectively. The wavelength on the west-
telephony, and it is now possible to state that bound transmission is 23 metres; in the other
this method of communication has become direction, from Tokyo to Santiago, the wave-
fully commercial. Single side-band circuits length is 23.5 metres.
are now in regular use between Great Britain The use of the ultra-short wave band for
and the United States, California and Hawaii, commercial purposes is to some extent limited
and Holland and the Dutch East Indies. by the general requirement of optical visibility
Similar circuits are planned between the U.S.A. along the propagation path. Nevertheless, there
and Germany, and the U.S.A. and Switzerland. are circumstances in which this band is of great
In at least two cases the system in use is not value. For example, the 9-channel U.5.W.
merely single side-band, but “twin channels,” telephone link between Belfast in Northern
i.e., two channels are fed from one transmitter Ireland and Stranraer in Scotland has been in
using side-bands on opposite sides of a common continuous service since August, 1937. The
suppressed carrier. The circuit improvements British Post Office and the French P.T.T. have
obtainable through single side-band working decided to supplement their cross-channel
in reduction of fading effects and improved cable service by an 18-channel U.S.W. link
quality are likely to be of special value during initially equipped for 9 channels. This equip-
the period of poor transmission conditions, due ment will contain “ weak talker” devices and
to sun-spots, anticipated about 1940. other improvements over the Belfast-Stranraer
“Development of the Multiple Unit Steerable system, and will operate on wavelengths between
Antenna (M.U.S.A.) is continuing, and arrange- 3.6 and 4.9 metres.
ments are being made for the erection of such A direct ultra-short wave service between
aerials in Great Britain and Germany. The England and the Scilly Islands was inaugurated
British Post Office is actively proceeding with in 1938 and a 6-channel U.S.W. link, manu-
the construction of a M.U.S.A. system near factured by the Nippon Electric Company, Ltd.,
the town of Rochester, Kent, England. The is being installed between Aomori Prefecture
ultimate equipment of this station will include a and Hokkaido in Japan, a distance of 75 km.
ELECTRICAL COMMUNICATION IN 1938 217
This Aomori-Hokkaido link is of interest since extensive system of radio beacons, over three
it contains a broadcast circuit equipped with a hundred in number, serving European and
compressor and an expander. An even longer North American waters.
2-channel U.S.W. link has been in operation The radio equipment for the new Cunard-
for some time between England and the White Star super-liner Queen Elizabeth will
Channel Islands, a distance of 136 km. be provided and installed by the Inter-
Tn addition to its use in fixed services, such national Marine Radio Company, Ltd.,
as in the examples quoted above, the ultra- (an associate of the I.T. & T. Corp.),
short wave band is now being extensively used the suppliers of corresponding equipment
for mobile services, and also by the broadcasting for her sister ship, the R.M.S. Queen
companies for short distance radio links to Mary. ‘The installation will follow the same
“outside broadcast” points to which wire general lines as the I.M.R.C. equipment
communication is not available. An interesting which has been found so effective in the
application to mobile services is the adoption earlier ship (enabling her to handle on her
of the ultra-short wave police system, originally maiden voyage the record traffic of 175000
developed in the U.S.A., by police authorities in paid words of telegraph traffic, 291 radio-
Norway, Sweden, Finland, Hungary and Holland. telephone calls, and 114 hours of broadcast
The outstanding application of ultra-short waves, programme), and will include the feature of
however, is in the field of aviation communica- separate transmission and operating rooms
tion and aids to navigation rather than to general with complete remote control of keying, power,
commercial radio link working. and wavelength from the combined operating
and reception room. The radio equipment in
MARINE RADIO the new Cunard-White Star liner Mauretania
For many years radio equipment of ships was will be required to meet the same high
almost entirely governed by the compulsory standard of performance set by the Queen Mary
regulations of the various maritime countries, installation.
applied in the interests of safety of life. There The first passengers’ radio telephone service
is now, however, a strong and growing tendency installed in British cross-Channel ships was
to equip ships to an even greater extent than the introduced in March, 1938, by the International
regulations demand. This tendency arises Marine Radio Co., on board the new British
primarily from appreciation of the fact that radio, and Irish Line’s motor vessels Leinster and
quite apart from its ‘‘safety of life’? aspect, can Munster. ‘This service, which was inaugurated
provide valuable assistance to the navigator. by an exchange of radiotelephone greetings with
It is significant that practically every new deep- the Queen Mary in mid-Atlantic, marks an
sea ship is now fitted as a matter of course with important advance in communication facilities
a radio direction finder, irrespective of whether for passengers travelling between England and
or not her tonnage or service is such as to bring the Irish Free State.
such fitting within the compulsory regulations. The ship-to-shore low power telephone
Moreover, on many large sea-going vessels, service to trawlers continues to show an increase
the radio direction finder is regularly operated in traffic, and facilities are now provided at
by the navigating officer as part of his normal coast stations in the north-east of Europe for
duties rather than by the radio staff. The the extension of such calls over the ordinary
same tendency appears in the case of the subscribers’ network. In the absence of any
“voluntarily equipped” class of vessel, such as special arrangements, these calls are handled on
the trawler or the small coasting vessel, which, a simplex basis.
n addition to being fitted with the skipper- The application of ultra-short wave sets to
operated radiotelephone equipment, already harbour craft with means for selective calling
accepted as a commercial necessity, now is arousing interest in ports, where the use of the
frequently has a direction finder as well. more usual marine wavelengths is attended with
Progress in this direction has been greatly difficulties.
stimulated in recent years by the growth of the In common with other services, marine radio.
218 ELECTRICAL COMMUNICATION
has been affected by the revision of the General system of direction finding have long been
Radio Regulations at the Cairo Telecommunica- known, but the commercialization of the system
tion Conferences (1938). The general effect of was slow, chiefly due to inherent difficulties in
this revision is to reduce to some extent the obtaining good balance between the component
frequency bands open to marine traffic, while aerials and in avoiding pick-up in the horizontal
at the same time excluding all other traffic from connecting leads. That these difficulties have
the more important bands. So far as ships are now been overcome is well illustrated by the
concerned, the frequency bands normally used experience of the French Air Ministry with
have been only very slightly modified; and a semi-portable Standard-Adcock equipment
because of the rather special economic and supplied by Le Matériel Téléphonique, Paris.
technical difficulties surrounding marine radio, This equipment is mounted in a motor van and
only a relatively low standard of frequency uses a pick-up system of insulated tubular metal
stability is required of marine transmitters which mast aerials connected to the goniometer
work in these ship bands. Ships using other through screened aperiodic transformers and
frequencies to which they are legitimately tubular transmission lines. The time required
entitled, but which are outside the bands just to complete the erection of a station is less than
mentioned, are required to have high. grade six hours, including the surveying necessary to
transmitters with frequency stability equal to ensure that the planes of the aerial pairs are
that of a land station. While this directly accurately at right-angles to one another, that
affects only a relatively small percentage of ships, all the masts are accurately vertical, and that
chiefly those of the passenger-carrying class, it the corner masts are rigorously equidistant
is likely to have a considerable indirect effect from the centre point, together with careful
on the design of all ship transmitters, in order laying of the earth mats and any necessary
to ensure that low frequency-stability trans- levelling of the site. The accuracy of bearings
mitters are not used outside of certain narrow and freedom from night effect secured with this
bands in which such operation is permissible. semi-portable equipment are fully equal to those
obtained from a well constructed permanent
AVIATION RADIO Standard-Adcock system.
While the use of radio as an aid to navigation For direction finding on medium wavelengths
is of increasing importance in the marine field, by ground stations, various forms of the Adcock
it is of paramount importance in the aviation system are to-day being widely applied. The
field, and progress during 1938 has been very impulse system of transmission, evolved as a
largely concerned with this aspect. Directional means of overcoming night-error, appears to
receivers are now fitted to almost all transport be losing favour. The use of Adcock direction
aircraft, sometimes in conjunction with dis- finders, which depend on the vertically polarized
charge aerials for the suppression of rain and component of the received signal, has reacted
snow static. Frequently the directional loop on the transmitting equipment used by aircraft.
aerials are mounted in streamlined casings; in With the high air speeds now in use the weighted
some of the latest designs, the nose of the trailing aerial becomes practically horizontal
aeroplane is made of non-conducting material and emits only a very small signal component
and, in these cases, it is possible to mount the with vertical polarization. It is, therefore,
loop system in the nose of the machine instead electrically preferable to employ a short fixed-
of externally and in a special casing. The study aerial giving a larger proportion of vertical
of different methods of using the properties of polarization, this preference being strongly
directional aerials to obtain bearings is still reinforced by mechanical considerations. Since
being vigorously pursued, and further improve- however, the radiation efficiency on mediur
ments have been made in the R.C.5 Standard- wavelengths of such fixed aerials is rather low
Busignies Automatic Radio Compass, the their adoption has been accompanied by :
inherently higher accuracy and operating speed demand for higher transmitter power in orde:
of which make it specially interesting. to maintain signal strength. This tendency tc
The advantages of the medium wave Adcock increased transmitter power is apparent botl
ELECTRICAL COMMUNICATION IN 1938 219
in Europe and America, as is also a tendency to by the use of aircraft direction finders as an
confine operation to spot-wavelengths. Modern auxiliary to the course beacons. In Europe an
aircraft transmitters are thus considerably more extensive triangulation system of non-directional
complicated than those of a few years ago and, radio beacons has been laid out to facilitate
in the interest of safety, many of the larger navigation over the principal routes for aircraft
transport planes carry a small emergency equipped with direction finders or radio com-
transmitter in addition to their main equipment. passes. Trials are also being made with rotat-
The application of the Adcock system to short ing beacons, but no definite conclusions have
waves continues to be the subject of much study, yet been reached as to the value of this
particularly in connection with long-hop trans- innovation.
oceanic flights, and is in regular use by one of Probably the outstanding feature of aviation
the American air lines. Whether complete radio to-day is the rapidly developing applica-
reliance can be placed on such a system still tion of the ultra-short wave band due to its
remains to be established, and the increasing well-known advantages for this class of service.
traffic on all air lines has forced the investigation The first use of the ultra-short wave band for
of other methods. aviation services was for instrument landing
Radio air navigation on the North American systems, and now nearly all the principal
continent has long been based. on the fixed AN airports in Europe are fitted with the Lorenz
course-beacon system, and is now further aided system of instrument approach. Work in
aerodrome. The
View showing Air-France pilots being trained in instrument landing at the Troyes
system uses.an. instrument landing system developed by Les. Laboratoires, Le Matériel Téléphomque,
landing ground
Paris, and consists of an ultra-short wave beacon giving a sharp line of approach to the
of the aeroplane
over a distance of 25 km, two ultra-short wave markers showing the horizontal position
The latter,
t during descent, ; gives the
along the axis, and one ultra-short wave glide path beacon.
with drawn
aeroplane accurate indications of the glide path to be followed, thus enabling the aeroplane,
curtains, to be piloted safely to ground. The complete aeroplane receiving equipment is compact and
weighs only 14 kg.
220 ELECTRICAL COMMUNICATION
America is progressing rapidly along similar for nearly all aircraft services have now been
lines and, whilst the results are not yet finalized, made in the ultra-short wave band, and it is
there is a general tendency to use shorter certain that development of suitable apparatus
wavelengths than in Europe in order to avoid for aerodromes and planes will proceed
interference between adjacent stations. In rapidly.
Australia a similar type of equipment has been The utilization of ultra-short waves for the
used for point-to-point navigation along lines measurement in an aircraft of its height above
similar to the AN beacon system ; the advantage ground represents an outstandingly interesting
claimed is complete freedom from false courses. development. The ordinary altimeter is subject
The marker beacon installations, used initially to variations depending on the prevailing
for providing fixes along the instrument ap- atmospheric conditions so that it is necessary
proach beacons, are finding universal application to apply corresponding corrections, the magni-
for procuring fixes along the AN systems in tude of which may alter, unknown to the pilot,
America and for marking obstructions. They during flight. An instrument with a response
have also been used in a modified form for the indicating directly the height above the actual
purpose of defining exactly the cone of silence ground, therefore, should be of great value.
over the AN beacon transmitters in view of The acoustic depth sounding devices now
the fact that the cone of silence produced by fitted on many ships are of this nature, their
the beacon itself is a negative rather than a response being proportional to the time taken
positive indication. by a signal emitted from the ship to return
As an outcome of experiments extending to the ship after reflection from the bed of
through the end of 1936 and the year 1937, the sea. Such devices are not readily applic-
Les Laboratoires, Le Matériel Téléphonique, able to aircraft, but ways are now being found
Paris, have developed an improved space track of applying the same principle by using radio
or instrument landing system for aircraft. waves rather than acoustic waves. Since
Three ultra-short wave channels between 33 and the velocity of radio waves is much greater
38 Mc are used; all transmitters are controlled than that of acoustic waves—186 000 miles/sec.
by low temperature coefficient quartz plates as against 0.2 miles/sec.—the time interval is
and use selenium type rectifiers. After a too short to be measurable with the required
preliminary demonstration in February, 1938, accuracy, and recourse is therefore had to the
before French officials, the new system was measurement of some change in the character
selected by Air-France, the French Air of the signal proportional to the length of path.
Transport Company, for training their pilots in An example of such an altimeter system is that
instrument landing (see illustration, p. 219). On demonstrated by the Western Electric Company
December 2nd, 1938, a very successful demon- during the year under review. In this altimeter
stration was given of the qualities of the system, the emitted signal is frequency modulated, and
and of the training of Air-France pilots before the change in signal character, used to measure
the experts of the International Air Traffic the height, is the average instantaneous
Association (I.A.T.A.), an organization com- difference in frequency between the emitted
prising representatives of all European Air wave and the wave received after reflection from
Traffic Companies. Great interest was the earth. The equipment operates on a
expressed by the visitors, and the indications frequency of several hundred megacycles, and
are that this new French system will find wide is reported to give accurate readings at heights
application in the near future. as low as about ten feet. Experimental work ona
Work is being done in both Europe and the rather similar system also is proceeding in
United States to ascertain the coverage of low Japan, and elsewhere studies are being made
power ultra-short wave equipment for purposes of altimeter systems which likewise use
of airport traffic control. In addition to freedom ultra-short wave emission, but measure the
from interference from other stations, a great height by reference to the change in phase of
gain in signal-to-noise ratio is being found under the carrier or any modulation imposed on the
conditions of snow and rain static. Allocations carrier.
ELECTRICAL COMMUNICATION IN 1938 221
VALVES previously ; the valves used in the repeaters
Whilst several new valve developments were are smaller and are tested to more exacting
achieved in 1938, the general tendency was to limits. The Bell Telephone Laboratories, Inc.,
extend previous knowledge of constructional recently demonstrated such a system with
methods to produce a wider range of valves, valves of small dimensions and very low operat-
particularly in the case of valves operating at ing powers; valves for this purpose also are
ultra high frequencies and capable of providing being developed by Standard Telephones and
considerable output at frequencies of the order Cables. In general, there is a tendency to use
of 150 megacycles. In general, advances in the the multi-electrode valve in preference to the
field of frequencies greater than 150 Mc were more conventional triode.
not very extensive; Standard Telephones and The advent of regular television services has
Cables, however, were successful in producing increased the demand for high-vacuum cathode-
micromesh types of valves yielding an output ray tubes and, as a result, a variety of large
of 15 to 20 watts at a frequency of 240 Mc. screen high-vacuum tubes has been produced.
For operation with these valves, the S.T.C. Interest lately has been centred round high-
valve laboratory developed a multiple valve vacuum tubes with magnetic focussing, and this
oscillator, and prospects of obtaining greater type of tube is now being produced by a number
output at the higher frequencies are promising. of firms. For vision amplifiers, special valves
Investigations into the properties of water- have been developed and, it is interesting to
cooled valves for high frequencies continued. note, the requirements for such valves are
Several valves, of a range of such valves very similar to those of valves for wide band
produced by Les Laboratoires, Le Matériel transmission systems. The need for small
Téléphonique, are cathode-ray tubes for general oscillographic
being used in the purposes also has become apparent, and
Eiffel. Tower ‘Tele- Standard Telephones and Cables have developed
vision Transmitter. a small tube with a 3” screen, as well as a
A number of monitor tube for use in cathode-ray oscillograph
manufacturers re- and triple tube units.
cently have shown Speech input equipment has developed along
interest in valves of the lines of quality rather than power output,
the cooled anode type requiring valves of high quality with respect
in which water cool- to noise and constant characteristics. For the
ing has been replaced production of the necessary valves with low
by forced air-blast noise, low microphonicity and close test limits,
cooling. Standard the introduction of special methods and equip-
Telephones and ment was required.
Cables recently The broadcast receiving valve has undergone
placed a 1 kW radia- a number of modifications and a tendency
tion-cooled double- exists to standardize on the American type
screen valve on the octal base valves. Other developments worthy
market. This valve of note are the low noise multi-electrode valves,
is capable of dissi- and improved frequency changers.
pating 1 kW on the
anode and uses anode SOUND POWERED TELEPHONES
potentials up to 2 500 The Bell Telephone Laboratories, Incor-
volts. porated, have developed a Sound Powered
In wide-band trans- Telephone requiring no battery supply for its
mission systems, a operation. Speech transmission and reception
ne
recent tendency is to are effected by means of a small balanced
1 kW Double-Screen employ a larger num- armature arrangement, and signalling by a
Valve
ber of repeaters than small hand-driven rotor acting in the magnetic
222 ELECTRICAL COMMUNICATION
designed and manufactured by the Bell 'Tele-
phone Manufacturing Company, Antwerp, was
installed in Prague and Brno. This equipment
forms the nucleus of a public Teleprinter switch-
ing network covering the whole country. Each
exchange area consists of one automatic and
one manual exchange, with a manual toll
position at Prague for the supervision of inter-
national calls. Local subscribers, toll line
subscribers and junctions are connected to the
automatic exchanges, whilst the manual
exchanges are used for providing broadcast
service and facilities for long period connections
between certain of the subscribers. ‘The meter-
ing of calls is accomplished by automatic ticket
registers which print on tickets the number of
the calling and called subscribers, the time, date
Sound Powered Telephone.
and period of effective call.
The use of Teleprinter systems was consider-
field of the balanced armature structure. ‘he ably extended by British railway companies
rotor generates 1000 p:s tone, which operates superseding Morse operation on a number ot
on the receiver of the called instrument. main line circuits. An important project plannec
This new type of telephone, despite its by The London and North Eastern Railway
rugged construction, weighs less than 2 Ib. involves the supply of Creed Teleprinters anc
Since it renders primary batteries with their automatic switching equipment to provide
inherent maintenance difficulties unnecessary, intercommunication between 25 initial stations
this type of instrument should find considerable located in the area between Manchester, York
application for marine and military purposes, Ipswich and London. The switching equip-
temporary service in connection with construc- ment, which was designed and manufacturec
tion projects, and general portable use. by Standard Telephones and Cables, London.
is arranged to handle heavy traffic over open-wire
TELEGRAPH lines.
A steady increase occurred in the general Plans for the provision of similar switching
appreciation of Teleprinter systems by systems by other British railway companies
Administrations and private users alike. One are under consideration.
reflection of this growing interest is revealed The process of consolidation effected by
by the active measures taken by several Euro- European Administrations in the extended use
pean Administrations towards telegraph —re- of Teleprinters is exemplified by the fact that
organization. A further indication is afforded the British Post Office and the French P.T.T.
by the resolution, adopted at the 1938 Cairo each acquired, during 1938, 200 additional
Telecommunication Conferences, providing for Creed No. 3 Teleprinters.
the setting up of a special Committee of the The Teleprinter Exchange facilities |connect-
C.C.1.T. to study the technical and economic ing Great Britain, Germany, Holland, Belgium.
considerations involved in the provision of Denmark, Switzerland and Czechoslovakia, are
international subscribers’ teleprinter services. utilized by a relatively small though growing
Widespread interest was displayed in projects number of business organizations. Strong
involving both manual and automatic switching grounds exist for the belief that, upon the
of private, national and international circuits removal of anomalies in technique and the
equipped with Teleprinters. One of the largest establishment of a uniform and more attractive
and most important of these projects matured tariff scale for international calls, a spontaneous
in Czechoslovakia where switching equipment, and universal growth of Telex will follow.
ELECTRICAL COMMUNICATION IN 1938 223
In Great Britain, a striking increase took
place in the demand for rented point-to-point
Teleprinter Services. Over 900 Creed Tele-
printers were acquired during 1938 by the
British Post Office for such services.
Creed. Teleprinters were supplied to the
New Zealand Post and Telegraph Department
to form the nucleus of leased wire services.
Interest in Stock Exchange and News tele-
printer services was well maintained. Numerous
machines were supplied to cater for new
subscribers to such services in London,
Liverpool, Alexandria, Bombay, Johannesburg
and Sydney.
The Press and News Distributing Associations
in the British Isles displayed an increasing New Creed Model 10-B Teleprinter.
tendency to discard Morse for ‘eleprinter
equipment, use being made under heavy traffic
conditions of multi-channel voice frequency condensed news items and pictures, reception
telegraph systems. taking place in the home in the form of a
Evidence of progress in the use of the Tele- miniature newspaper. In its present form,
printer system by Meteorological services for reception can be effected either by a special
the transmission of weather reports is furnished facsimile recorder or by an additional unit
by the greatly increased number of machines connected to an existing broadcast receiver.
supplied for installation at aerodromes in The received signal appears at the recorder in
Great Britain and several other countries. the form of normal newsprint feeding from a
A new transmitting and receiving Tape paper roll on the recorder. One system utilizes
Teleprinter,® designated Model 10-B, was black print on white paper, and another, red
developed by Creed and Company, Limited. print on black paper.
Consistent progress was made in perfecting
existing Teleprinter systems. SELENIUM RECTIFIERS |
In the radio printer field, a “built up” The forecast in last year’s review of
character Radio-printer,® utilizing seven fre- increasingly diverse applications of selenium
quencies, was developed by Les Laboratoires, rectifiers has been amply justified. New
Le Matériel Téléphonique, Paris. Field trials, rectifier apparatus has been developed for
were highly successful. welding, plating, cinema arc projectors, electric
vehicle charging, lift control, etc. Standard
FACSIMILE TRANSMISSION Telephones and Cables, London, are now
Picture or facsimile transmission over wire or constructing a 14000-ampere rectifier for
radio circuits has come to be regarded as a electro-plating purposes, and the British Broad-
normal function of communication systems, and casting Corporation has installed two large
the development of facsimile transmission for equipments for supplying plate current in
domestic use is now engaging considerable its new Empire short wave station at
attention. Daventry.
A recent development of this character, Further advances in all-mains telephone
known as Facsimile Broadcast, is undergoing supply rectifiers were achieved during the past
tests in the U.S.A. by more than twenty broad- year. An outstanding development of Le
casting stations specially licensed by the Federal Matériel Téléphonique, Paris, is a new scheme
Communications Commission. It visualizes com- of voltage regulation which maintains constant
mercial broadcast transmitters being used during voltage irrespective of load or supply fluctua-
non-programme hours for the transmission of tions.
224 ELECTRICAL COMMUNICATION
TOTALISATORS mission and sound engineering problems anc
The growing use of electrically operated supplied all microphones and amplifiers witl
totalisators on racetracks seems worthy of associated mixers, as well as the line amplifier
mention as indicating another adaptation of and some of the loud speakers and powe
telephone apparatus and principles to systems amplifiers.
for rapidly communicating results to the public. A number of interesting Public Addres
The Union Totalisator System is manu- installations was designed and supplied bh
factured by Standard Telephones and Cables, other Companies of the I.T. & T. group
Limited, London, which installed nineteen notably the Bell Telephone Manufacturin;
equipments of this type in 1938, and a total to Company, Antwerp, and Le Matériel Télé
date of eighty. phonique, Paris.
PUBLIC ADDRESS RAILWAY SYSTEMS
With more general recognition of its The development of the Standard railwa:
advantages, interest in Public Address signal interlocking system was completed i
equipment is increasing. ‘There are indications, 1938, and an order obtained for the interlockin;
too, that architects are tending to give more of the important London and North Easter
consideration to acoustic characteristics. It may Railway junction at Doncaster, England. Th:
consequently be expected that, in the future, system is designed to enable a signalman t
Public Address or Speech Reinforcement handle traffic with the maximum flexibilit
systems will be utilized with greater effective- consistent with complete safety, and incorporate:
ness. motor-driven switch-gear of the type used it
Air Raid Precautions schemes and staff calling Rotary automatic telephone systems.
arrangements for large buildings and factories The total number of contacts involved in thy
are calling for high powered Public Address interlocking of a particular area with this systen
equipment operating a large number of loud- approximates one-seventh of the numbe
speakers. During the year, installations were required in the older panel systems at presen
made by Standard Telephones and Cables, inuse. Actual control of interlocking is effectec
London, for the Westinghouse Brake and from a control desk in the form of a track plar
Signal Company at Chippenham; for the of the area with miniature switches mountec
Fairey Aviation Works at Hayes; for the S. T. at points corresponding to the signals, etc., tc
& C. Factory, New Southgate; and for the be controlled. ‘This geographical layout of thi
Southampton Fire Station, where automatic control panel gives the signalman a clear recor¢
means are employed for changing over to of the state of the track and relieves him of thi
battery and motor converter supplies in case of necessity of remembering the sequence of poin
mains failure. and signal operations required for setting uj
Public Address systems were used in conjunc- any desired route.
tion with General Post Office lines for relaying
programmes on a large scale to a number of FIRE ALARM SYSTEMS
centres. Examples are a programme relayed The London Fire Brigade, in 1930, installec
from Glasgow to Ayr, Paisley, Falkirk and a Standard-Gamewell Fire Alarm System at the
Edinburgh ; and one, over 150 miles of land Southwark Area as an experiment. It is stil
line circuit, between Limerick and Drogheda. in service, and, having proved satisfactory
A permanent loudspeaker installation is now similar systems have been installed in the new
in use at Westminster Abbey. It includes a Headquarters Area and also in one of the
large number of low-powered loudspeakers. important Divisions in the City. Orders
Contributing to the marked success of the have now been received for the remaining five
34th International Eucharistic Congress, held in Divisions of the London Fire Brigade.
Budapest, May 22-29, 1938, was the Public New Fire Alarm systems have been suppliec
Address equipment. Standard Electric Com- and installed in Belfast, Rugby and Dagenham.
pany Limited, Budapest, handled the trans- The Belfast system consists of 110 street boxes
ELECTRICAL COMMUNICATION IN 1938 225
together with equipment in the Headquarters without loss of clarity of the diagram for
station and three substations. The Rugby operating purposes. ‘This is an important
system consists of 30 Fire Alarm and Ambulance factor when a large number of substations
Boxes and station equipment. The system at must be controlled from one control room. A
Dagenham consists of 64 Fire Alarm and typical new type control diagram and desk is
Ambulance Boxes and station equipment. illustrated in the accompanying illustration.
In the Dagenham and Rugby stations, a new The D.C, bias multi-service system, reported
feature is the incorporation of a Control Desk last year for the control of street lighting, has
as a part of the Fire Alarm Switchboard. been further developed to control “off-peak”
loads and air-raid warning devices. An
REMOTE CONTROL AND’ SIGNALLING important development applies the same
SYSTEMS principles to high tension cables between sub-
Remote control and indicating systems stations and renders interconnecting pilot wires
employing variable frequency metering for the unnecessary.
control of one or more sub-stations over a The Nippon Electric Company, for some
single pair of wires are rapidly consolidating years, has produced remote control and power
into an essential feature of power transmission, line carrier telephone apparatus. The Company
distribution and railway electrification. is now manufacturing carrier telephone equip-
Developments include various apparatus unit ment for operation over a 110 000-volt line,
designs, notably the combined control key and including means for remote control over the
indicating lamp, which enables the size of same channel of oil circuit breakers, and quick
control diagram boards to be kept to a minimum acting battery switching and protective features.
Typical New Type Control Diagram and Desk.
226 ELECTRICAL COMMUNICATION
For remote control, a standard 2-stage syn- of the Société de Transport d’Energie Centre-
chronous system is used. The carrier current Ouest (SATECO), serving Eguzon, Distré,
is modulated by four frequencies. The equip- Angouléme, and Bordeaux. The distance be-
ment will be placed in operation early in 1939. tween extreme points of the network is 600 km.
POWER LINE CARRIER POWER CABLE
Compagnie des ‘Téléphones Thomson- The power cable field shows evidence of
Houston, Paris, during 1938, manufactured considerable activity in the so-called super-
and installed over thirty high tension telephone tension range or class. The problem of
carrier and selective protection equipments on transmitting large units of energy is promoting
French power distribution networks varying in two distinct lines of system development.
voltage from 60000 to 220000 volts. The On the one hand, Power Supply Companies
most recent installation is that on the system are more disposed to employ higher trans-
mission voltages due to
the cost of switchgear,
capable of handling
larger amperage, and of
reactors for limiting
fault current. This
tendency is accentuated
by the practice of inter-
connecting power sta-
tions. They are, con-
sequently, raising their
maximum transmission
voltage from 6.6-kV to
33-kV and from 20-kV
to 60-kV or 132-kV.
Enquiries for 150-kV
and 220-kV cables, in
fact, are becoming re-
latively common, and
practical realization of
some of the schemes
under consideration
may be expected in the
near future. During
1938, for example,
Holland commenced
installing a 150-kV
system. -
On the other hand,
there are certain cases
in which high amperage
per transmission circuit
may be economically
justifiable; for example,
where the transmission
2.20 RV Power Line Telephone Carrier Equipment (with cover removed) of the line must be installed
type installed by Compagnie des Téléphones Thomson-Houston, Paris, on Power in existing duct lines.
Distribution Networks.
Demand is, therefore,
ELECTRICAL COMMUNICATION IN 1938 227
also arising for an increase in the current points, or the need for subsequent maintenance
carrying capacity of supertension cables, i.c., for of oil levels, etc. It is also claimed that the
higher operating temperatures. impulse strength of this type of cable is superior
To the requirements for higher voltages and to that of the others.
higher operating temperatures must be added The probabilities are that the characteristics
an increasing demand for improved resistance of the three above-mentioned fundamental
to surges, transients, etc., which are more apt types of cable will be modified by further
to. occur in power systems including high developments. Accurate forecasting of their
electrostatic capacity cables connecting a number future relative merits is therefore, obviously
of generating stations separated by considerable impossible.
distances. In the Laboratories of Standard Telephones
Oil-filled cables continue: to’ give satisfactory and Cables it is believed that the performance
service and are being installed in considerable of any type of supertension cable will be
quantity, and solid type cables are gaining more determined largely by the insulating materials
and more favour, particularly for 60-kV available and by the processes employed in
transmission at moderate amperage. There constructing the finished insulation: During
are, nevertheless, signs of keen competition 1938, therefore, much work was carried out on
arising from “‘pressure”’ cables for high voltages, the production of impregnated paper of high
high operating temperatures, etc. dielectric strength, low dielectric loss and other
Towards the end of 1937, a 132-kV gas- desirable characteristics. In farticular, an
filled cable was installed for trial in the British effort was made to improve the economics
Grid, and this cable has apparently given of commercial processes for manufacturing
satisfactory service. Objections raised to this acetylated styrenated paper. The introduction,
type of cable are alleged limitations with respect in 1939, of this material into supertension cable
to impulse (surge) strength and high amperage. design may produce radical changes in the
The latter limitation is deducible from the high performance of various types of cable. Cable
thermal resistance of the gas filling the inter- . system performance is also becoming more and
stices. It remains to be seen how far these more dependent on the behaviour of the joints
disadvantages can be eliminated by subsequent and incorporated terminations. The number of
development. Other types of gas-filled cable styrene joints and terminations installed during
ate known to be approaching commercial the past year increased considerably and the
production. indications. are that this increase will be
Up to 1938 the Hochstadter pressure cable— accelerated.
there are some seven installations at 60-kV In the general dielectric field, further develop-
to 110-kV in service—suffered from the ment took place in synthetized or polymerized
restriction that the cable had to be enclosed in a dielectrics. None of these, however, has so far
high pressure, welded steel pipe. ‘Such pipes made great progress commercially. One of the
are none too acceptable to Power Transmission more notable materials of this class introduced
engineers; they, for example, have impeded during 1938 is Polythene, i.e., polymerized
the exploitation of the Oilstatic Cable in the ethylene.
U.S.A. Now, however, the pressure cable has
IT. & T. OPERATING TELEPHONE
appeared in a self-contained (double lead
COMPANIES
sheath) form and two installations of this
modified type are in progress in England. The Telephone operating subsidiaries of the Inter-
claim for this type is that it can be produced national Telephone and Telegraph Corporation
for simultaneous working at high electrical gained more telephones in 1938 than in any
stress and high operating temperature. ‘These other year in their history. They have reported
two characteristics afford advantages compar- a net increase of 76 080 telephones for the year.
able with or greater than the oil filled cable, The previous record gain was in 1929 when the
and are obtained without added expense, and net increase was slightly more than 70000
awkward (from a space point of view) feeding stations.
228 ELECTRICAL COMMUNICATION
The large system of the United River Plate cut-over to Rotary automatic operation ; also,
Telephone Company in Argentina contributed the first step in an extensive long distance
a gain of approximately 25 850 stations. ‘The underground cable programme was taken when
Shanghai Telephone Company, with a net in- a 65 km section of underground toll cable was
crease of 17 860 telephones for the year, regained cut into service between Bucharest and the
not only the number of telephones withdrawn important oil centre of Ploesti. ‘Two cables of
from service during the hostilities around the most modern design and suitable for 12-
Shanghai in 1937 but added. several thousand channel carrier operation were placed over this
more to advance to the highest development in route and extensions to Brasov and Buzau are
its history. The Rumanian Telephone Com- in process of manufacture. In Chile, 5 00C
pany gained 11800 telephones, the Chile lines of automatic equipment were added in
Telephone Company 7 200, the Mexican Tele- Santiago and Valparaiso; a 400 km toll cir-
phone and Telegraph Company 5 500, and the cuit was constructed between Santiago and
systems in Peru, Southern Brazil, Cuba and La Serena, connecting the important naval base
Puerto Rico reported substantial increases of Coquimbo with Santiago; and _ radio
relative to their size. telephone service was opened with Japan. In
Along with the Shanghai Company, the I. T, Rio Grandense Province, Brazil, work is in pro-
& T. telephone operating companies in gress on a new 220 km toll line linking Porto
Argentina, Chile, Southern Brazil, Peru, Mexico, Alegre with the important interior town of
Rumania and Puerto Rico had all achieved a new Santa Maria.
record high development at the end of the year.
Furthermore, new record levels of toll and IN MEMORIAM
long distance telephone usage were established The death on June 11th, 1938, of Ministerial-
in the territories served by these companies. direktor Karl Hépfner of the German Post
They show that approximately nine per cent Office, well-known internationally for his im-
more domestic and international long distance portant articles in technical journals and his
calls were completed in 1938 than in the pre- valuable contributions to the development of
vious year which, for most of the LT. & T. long-distance telecommunications, is regretfully
telephone operating companies, was a record recorded. As Chairman of the Third ‘‘Com-
year for toll traffic. mission de Rapporteurs”—a position in the
Approximately 71% of all telephones in C.C.1.F. to which he was appointed in 1927—
I. T. & T. operating companies are now auto- Herr Hopfner was closely associated with com-
matic. More than 63000 stations were con- munication experts in many countries. A man
verted to dial operation in 1938, principally in of vision and great ability, he impressed all with
Rumania, Argentina, Chile and Peru. whom he came in contact by his impartiality,
Despite the variety of conditions involved in his unfailing kindliness, and charm of per-
the operations of the telephone companies, about sonality.
80% of all service orders received in 1938 were On November 15th, 1938, a great French
completed within three days. scientist—André Blondel—passed away. Mr.
In the construction and extension of facilities, Blondel was born at Chaumont in 1863, and
the 1938 projects included the following: In gained international recognition for his import-
Argentina, 21000 lines of step-by-step auto- ant and far-reaching contributions to the
matic equipment were installed; radio- science of electrical engineering. To his. credit
telephone service was extended to Algeria, may be placed a number of inventions, including
French Morocco and Tunisia; international the oscillograph for measuring the instantaneous
telephone service was opened with 51 central value of an electric current, holophane globes
offices in Uruguay ; connection was established and radiogoniometer, as well as contributions of
through construction with the telephone net- a fundamental nature in the field of electric
work in three important northern provinces, power transmission, electric alternators and
providing Argentina with a complete national motors, photometry, wireless telegraphy, acous-
system. In Rumania, five additional cities were tics, submarine signalling, etc. He presided
ELECTRICAL COMMUNICATION IN 1938 229
over both national and international committees (2) National Dialling :—-
“Automatic Long Distance Switching—Rotary
and commissions; and, in recognition of his System,” by J. Kruithof, ei, and M. den
services, he was elected Membre de |’Académie Hertog, Electrical Communication, January, 1934.
des Sciences in 1913, and Commandeur de la “Automatic Long Distance Switching—Impulse
Transmission,” by S. Van Mierlo and T. S.
Légion d’Honneur, as well as Honorary Member Skillman, M.A., Electrical Communication,
of The Institution of Electrical Engineers, January, 1934.
London, and of the American Institute of (3) Micro-Ray Radio :—
Electrical Engineers, New York. He was also ““Micro-Ray Radio,” Electrical Communication,
awarded the Kelvin and Mascart Medals.
July, 1931.
“Production and Utilization of Micro-Rays,” by
The careers of ‘Takesaburo Akiyama, A. G. Clavier, Electrical Communication, July,
Chairman of the Board of Directors of the 1933.
“The Anglo-French Micro-Ray Link between
Nippon Electric Company, Limited, Tokyo, Lympne and St. Inglevert,” by A. G. Clavier
and of Fumio Shida, Managing Director of the and L. C. Gallant, Electrical Communication,
Nippon Electric Company, Limited, are briefly January, 1934.
outlined in the October, 1938, issue of this (4) Single Side-~-Band Short Wave Radio :—
“The Single Side-Band System Applied to
journal. Officers and members of the Inter- Short Wavelengths,’’ by A. H. Reeves, Electrical
national System throughout the world knew Communication, July, 1931.
and, in some cases, worked intimately with these “The Spread Side-Band System on Short Wave
Telephone Links,” by L. T. Hinton, A.C.G.1.,
distinguished gentlemen. Both were held in B.Sc., A.M.I.E.E., Electrical Communication,
high esteem and affectionate regard, and their October, 1931.
passing has caused keen sorrow and a deep “The Single Side-Band System applied to
Short Wave Telephone Links,” by A. H.
sense of loss. Reeves, Journal of the LLE.E., September, 1933,
The International System and the com- page 245,
munity, on November 12th, 1938, suffered a (5) “The Belfast-Stranraer 9-Circuit Ultra-Short
Wave Radio Telephone System,’ by D. B.
severe loss in the passing of Clarence Hungerford Mirk, B.Sc., M.I.E.E., The Post Office Electrical
Mackay, whose career is given in outline else- Engineers’ Journal, April, 1938.
where in this journal. (6) “Bristol-Plymouth 12-Channel Carrier System,”
Sournal of the LLE.E., November, 1937, pp. 573-
606 ; Electrical Communication, October, 1937.
REFERENCES
(7) “A Working Standard for Telephone Trans-
(1) Automatic Ticketing :— mission,” by L. C. Pocock, Electrical Com-~-
“Automatic Ticketing of Telephone Toll Calls,” munication, July, 1938.
by Leslie B. Haigh, Electrical Communication,
(8) “The Creed No. 10 Tape Teleprinter,”’ by A. E.
April, 1937. Thompson, Electrical Communication, April,
“Automatic Printing Register for Telephone
1938.
Call Recording,” by L. Devaux, Electrical Com-
munication, April, 1937. (9) “L.M.T. Laboratories 7-Frequency _ Radio-
“Automatic Ticketing of Toll Calls,” by E. P. G. printer,” by L. Devaux and F. Smets, Electrical
Wright (in this issue). Communication, July, 1938.
The Application of Automatic Ticketing to Step-by-Step
Systems
By E. P. G. WRIGHT, M.I.E.E.,
Standard Telephones and Cables, Limited, London, England
TICKETING ASSOCIATED WITH P.A.B.X. with the rotary system. The identity of the
EQUIPMENTS called party is obtained from the digits as they
OLLOWING on the introduction of are dialled. In addition to the time at which
HK automatic ticketing for toll calls in the the call occurred, the identity of the exchange
Bruges rotary area by the Belgian line is also recorded. The installation referred
Régie,! the first installation of automatic to could not be arranged to indicate the duration
ticketing has now been made with step-by-step of calls because of the fact that the standard
equipment. director type exchange in the London area
This new installation is not concerned does not provide any signal when the call is
exclusively with toll calls but serves to provide answered other than the discontinuance of the
detailed information as to the origin and ringing tone. In the case of P.A.B.X. equip-
destination of traffic passing from a private to ments connected to provincial type exchanges,
a public service. The necessity for some however, the direction of current from the
automatic means for recording the details of transmitter battery is reversed at the time of
this type of traffic has grown up with the answer, a condition that could be used to start
general increase in the distance over which the the timing switch for recording the duration
subscriber is permitted to dial. In the past, of the call, i.e., up to the time of release.
it has been possible to prevent long distance
calls being established without reference to the
USE OF TICKETING APPARATUS FOR
P.A.B.X. attendant by means of the discrimina-
SERVICE OBSERVATION
tion of equipment responding to one or a series
of digits. More generally, unauthorized connec- A similar application of automatic ticketing
tions to the public service are controlled by could be used with step-by-step equipment to
causing all such calls to be established by the eliminate the. work of an observation operator
attendant. in providing a detailed record of calls originating
The purpose of the automatic ticketing from one or a number of lines. In such cases
equipment as used with a P.A.B.X. is not to the ticketing equipment would be installed in
prevent the establishment of long distance the public exchange and associated either with
calls, but to provide a written record of such the subscriber’s line circuit or with the first
calls, including the identity of both parties and selectors serving the lines on which observation
the time of making the calls. is required. ‘lhe record so obtained would
The method of identifying the calling indicate the number of calls made, the identity
extension depends on the use of a tone connected of the party called, the time elapsing while the
to the third wire by the outgoing relay group called subscriber is being rung and the duration
in substantially the same manner as that used of the conversation. If identification is applied
throughout the area, the ticketing equipment
1 “Automatic Ticketing of Telephone Toll Calls,” by may be used for the observation of incoming
L. B. Haigh; and “Automatic Printing Register for as well as outgoing calls. As the ticketing
Telephone Call Recording,” by L. Devaux; Electrical
Communication, April, 1937. apparatus is arranged with plug connections,
230
AUTOMATIC TICKETING 231
the observation service can be readily moved Not only can such an arrangement provide
from one exchange to another. relief to the operators with the probability of a
more efficient service, but, in addition,
NUMBER CHECKING advantage may be taken of the ability of the
machine to calculate the exact charge for calls
Subscriber identification has other more
important possibilities in connection with a no- thus established by the operators. The charge
delay toll service. The operation of “‘no-delay”’ for a call is dependent on the location of the
exchanges of the calling and called parties, the
or demand positions assumes that the provision
of toll lines is sufficient to enable a large per- duration of the call, and the time of the day or
centage of calls to be completed without night when the call is made. All these data
are at the disposal of the machine, and the actual
asking the caller to replace his instrument and
calculation can be completed and printed on the
await the connection. Since such calls are
not reversed, the identification information
ticket within a period of a few seconds.
given by the subscriber cannot be checked by In much the same way that demand operation
is initially introduced over a few routes during
the call reversal process. In fact, on a “no-
delay” call, the operation of checking the the slacker periods of the day—and generally
identity of the calling subscriber often consumes finds increasing application as the line plant
as much time as is required to obtain the grows—it may come to pass also that subscriber
toll dialling will commence on a few routes
wanted toll subscriber. The difficulty which the
carrying a relatively large amount of traffic.
operator experiences in identifying the caller
The installation of subscriber identification
is increased on P.A.B.X. lines, especially as the
circuits makes it practicable to produce tickets
latter may be unaware of the number of the
automatically wherever subscriber toll dialling
particular exchange lines being utilized. If the
is possible, and the facility can be extended if
caller is using a night-line number, it may not
and when desired.
be in the same consecutive group as the main
P.A.B.X. number, so that the toll operator may
become involved in a rather complicated search. SUBSTITUTION OF TICKETING
With the identification circuits, the ‘“demand”’ APPARATUS FOR MULTI-METERING
positions on the toll board may be fitted with
Another application of automatic ticketing is
number indicators carrying as many as 7 or 8
concerned with the handling of quite short
digit wheels. These indicators are set up
toll traffic of the type introduced in many areas
automatically under control of the identification
with the aid of multi-metering equipment.
circuits and involve minimum effort for the
Although very comprehensive schemes have
operators. Such an arrangement has already
been adopted in different areas, there are certain
been introduced with rotary equipment at
Ostend.
difficulties in introducing multi-metering
facilities with some step-by-step equipments.
For example, some exchanges employ a message
THE PRINTING OF OPERATORS’ TICKETS
register with a locking contact which is designed
The recent trend of development visualizes to hold the message register in its operated
the use of voice frequency dialling over long condition for the duration of the call; and, in
distance circuits, and considerable progress order to permit several operations, the circuit
has already been made in introducing 50-cycle conditions must be radically altered. Similar
and other similar arrangements for dialling changes must be incorporated if the message
over shorter toll lines. It seems worthy of register is arranged to operate from a booster
emphasis that the combination of operator potential unless the message register is designed
toll dialling and subscriber identification to release on the normal exchange voltage.
facilities makes it a possibility that the practice These difficulties are avoided with automatic
of producing toll tickets automatically, without ticketing, which provides the further advantage
special effort on the part of the toll operator, that the discriminating equipment can be more
will find rather wide application in the future. readily centralized because there is no longer
232 ELECTRICAL COMMUNICATION
any necessity for passing back-metering impulses the general use of mixed digit number schemes
over two-wire junctions. Furthermore, some in step-by-step areas tends to make more
telephone Administrations are under. an obliga- dificult the determination as to when the
tion to supply their subscribers with details of complete number has been dialled. This
calls exceeding a certain value; but such calls, difficulty can be overcome at minimum expense
with multi-metering equipment, can be handled by arranging for the process of identification to
only with the assistance of an operator, whereas, commence only when the answering signal is
with automatic ticketing, no special treatment received.
is required. Evidently, there is considerable scope for the
In the application of automatic ticketing to application of automatic ticketing, not only in
step-by-step equipment, the same general connection with toll traffic but also within
principles can readily be applied as those multi-exchange networks for promoting more
already introduced in the field in connection efficient operation. The production of a
with the rotary systems. In many step-by-step printed traffic record in effect provides a new
exchanges, release is controlled from the out- technique which seems destined to prove
going relay group, thus providing direct access advantageous to Administrations and private
to the third wire and consequently simplifying companies in the solution of their maintenance
the process of identification. On the other hand, and traffic problems.
Portion of stand of Fabbrica Apparecchiature per Comunicaxioni Elettriche at the Milan Radio
Exhibition, 17th-25th September, 1938. It included commercial radio transmitters and receivers,
and pictures of the Rome 100 kW Short Wave Broadcaster installed by F.A.C.E. for the ELAR,
the Italian Broadcasting Company. This broadcaster was inaugurated on 31st October, 1938.
Administration Building—Belgian Air Ministry, Brussels.
Airport P.A.B.X. Network
By R. T. RINGKJOB
Bell Telephone Manufacturing Co., Antwerp, Belgium
INTRODUCTION Service messages are transmitted by means of
HE Belgian Administration for Civil teleprinters, which are particularly suitable for
Air Transport operates four airports, this type of operation.
located at Brussels, Antwerp, Ostend The four national airports at Brussels,
and Zoute. Regular national services, both Antwerp, Ostend and Zoute have had the
freight and passenger, are handled through them advantage of a separate telephone network for
as well as considerable international traffic. several years.. Until recently, magneto pony
To be successful, conveyance by air must meet switchboards were utilized at each flying field,
the same regularity and safety requirements a few local battery subsets being installed at the
as other types of transportation. No means of most important points. The old ring-down
achieving this result must therefore be neglected. methods, with the inherent. disadvantages of
Particularly important in reducing un- manual operation, did not, however, satisfy
certainties in air travel and ensuring a smoothly the exigencies of the Administration, and it was
functioning organization is direct telephonic decided to install a modern private automatic
or telegraphic intercommunication between exchange system, which would give any station
airports for service purposes. Thus, the latest at any airport access to any station at any other
reports of weather conditions can be made flying field without the intervention of an
available immediately prior to the departure of operator.
an airplane, loss of time in establishing a toll The Administration accordingly ordered four
connection over the regular national communica- P.A.B.X.’s including interworking equipment
tion network being avoided. Similarly, last from the Beli Telephone Manufacturing
minute information as to freight awaiting Company, Antwerp. The system was placed
transportation, freight space available, supplies in operation early in 1938, and has given very
required, passenger lists, etc., can be rapidly satisfactory results.
transmitted. Interworking amongst the four airports
Recognizing the great value of direct inter- involved special problems, due partly to their
communication, most large airports now operate wide separation, and to the necessity of
their own lines to other flying centres. The equipping the loaded cable pairs with voice
Brussels airport, for example, has direct lines frequency repeaters. Inasmuch as ordinary
to Amsterdam, Cologne, Paris and London. D.C. dialling could not be used, it was found
233
234 ELECTRICAL COMMUNICATION
necessary to resort to 50 cycle signalling, JUNCTION DIAGRAM
applying the same principles as in automatic Fig. 2 illustrates the fundamentals of the
long distance dialling systems. system and the routing of the different classes
The purpose of the present article is to of calls. It will be seen that each station, with-
describe some design and operating features of out the intervention of an operator, has access
the P.A.B.X. system installed in the Belgian to all other stations in the entire network.
airports. All P.B.X. stations have automatic outgoing
service to the local city exchanges or to the toll
EQUIPMENT office.
TABLE I In the 7035 P.A.B.X., incoming city and toll
Stations traffic is handled by an attendant, who extends
Type of Tie
Location | P.A.B.X.] Cap. | Eqpt. | ‘Trunks Lines such calls to the local stations by means of a
high speed cordless attendant’s set.
Brussels 7035 50 40 3 3
Antwerp 7011 6 6 1 1
The 7011 boards are unattended. Any
Ostend FOU 6 6 1 1 P.A.B.X. stations can answer incoming calls and
Zoute 7011 6 6 1 1
transfer them to the interested party by means
of the well-known call back and transfer
Table I contains data on the P.A.B.X.
feature.
equipments installed at the four airports. ‘The
The circuits are designed so that a city
P.A.B.X.’s (Nos. 7011 and 7035) are of standard
connection in one P.A.B.X. cannot be extended
Bell Telephone design, and have been described
via a tie line to a subscriber in another P.A.B.X.
in detail previously.t A view of the 7035
board installed in Brussels is shown in Fig. 1.
TIE LINES
The location of the four P.A.B.X.’s is
indicated in Fig. 3. The Brussels P.A.B.X. is
connected by means of one tie line to each of the
three other boards. The Brussels P.A.B.X.,
therefore, serves as a tandem point, and a
connection between any two of the outlying
P.A.B.X.’s passes via Brussels and makes use
of two tie lines.
The tie lines are rented from the Telephone
Administration and are included in the main
toll cables between the various towns. The
characteristics of these lines are given in
Table IJ. In Ghent, two of the tie lines are
provided with voice frequency repeaters with
50 cycle by-passes.
50 CYCLE DIALLING
Due to the distances between the various
P.A.B.X.’s, it would not be feasible, as already
mentioned, to operate the tie lines on a D.C.
signalling basis. Dial impulses, as well as other
necessary signals, are therefore transmitted by
means of 50 cycle alternating current.
1“ Private Automatic Branch Exchanges,” by W. Hatton
and R. T. Ringkjob, Electrical Communication, January,
Fig. 1—No. 7035 P.A.B.X. installed in Brussels Airport. 1936,
AIRPORT P.A.B.X. 235
5 7O0Hl- P.A.BX. BRUSSELS 7035-P.A.B.X.
ANTWERP
LF LF Ss
A TLF TLF
Le {50~}-— {50~} :
TF TH |
TO CITY e-roye)
wes r=
OSTEND LF 5 7ON-P.A.B.X. TLE
(f +) 506 z
cal
— :
“e’ TLE TF
| ( a {50~} 70 ciTy ——_’/
TF
_—= TO CITY
ZOUTE LF 5 7OIL- PA.BX. |
ou TLE
)
~S {50~}—
TF
7O CITY
Fig. 2—Function Diagram.
The principles of the receiving and sending re-transmits the substation dial impulses to the
circuits are substantially the same as those used distant end. Fast and slow dials, long and short
in automatic long distance telephone practice.* lines, as well as poorly insulated lines on the
Special precautions were necessary to obviate flying fields, therefore, all have a direct
impulse distortion. repercussion on the impulse transmission.
In ordinary toll connections, the originating To overcome these difficulties, specially
TABLE II
Distance Diameter
Line inskm in mm | Loading
Brussels—Antwerp Phantom 50.9 18 177/63 mH at 1830 m
Brussels—Ostend » 126 1.5 ” ”
Brussels—Zoute » 126 1.5 ” ”
dial impulses are transmitted by a home designed impulse correctors are included at the
register ; hence, the stepping conditions at the tandem point and, also, in the receiving portion
receiving end are relatively uniform. In the of each tie line.
P.A.B.X. network, however, the originating It may be of interest to note, incidentally,
substation is connected directly to the outgoing that a tandem connection is built up on the
end of the tie line, the stepping relay of which principle of forward dial impulses. A short
50 cycle starting impulse engages a distant tie
2 A Field Trial of 50 Cycle Signalling on Toll Lines,”
by W. Hatton, Electrical Communication, October, 1936.
line circuit, and a connection is broken down by
236 ELECTRICAL COMMUNICATION
means of a long 50 cycle impulse sent out when picks up the calling line, releases the local link
the originating party hangs up. and sends out a short A.C. impulse which
engages the distant tie line circuit in Brussels.
NUMBERING SCHEME The latter sends back dialling tone, and “A”
The whole system was worked out on the basis now dials the remaining digits, say “74.”’
of uniform numbering, i.e., a subscriber is The “7” directs the Brussels tie line finder
always called by the same number regardless to the outgoing tie line to Ostend and, during
of the location of the calling station. On purely the interval between ‘7’ and ‘‘4,” the latter
local calls, however, the prefix is omitted. The circuit transmits a short A.C. impulse to the tie
numbering scheme is shown in Table III. On line circuit in Ostend.
The last digit ‘4’ is received on the tie line
TABLE III
finder in Ostend (re-transmitted and corrected
by Brussels) ; thus, subscriber No. 4 is selected.
Directory Local
Number Prefix Numbers Subscriber “B’’ (No. 4) is rung in the usual
manner and, upon removing the receiver,
Brussels 99-10. to 99-59 99 10-59
Antwerp 66-0 to 66-5 66 0-5 conversation ensues.
Ostend 77-0 to 77-5 77 0-5 When “A” hangs up, a long A.C. impulse is
Zoute 88-0 to 88-5 88 0-5
sent out, and all circuits are released.
On connections between Brussels and out-
local calls, the local number (1 or 2 digits) is lying P.A.B.X.’s, and vice versa; the second
dialled on receipt of dialling tone. On tie figure of the prefix serves no useful purpose and
line calls, the first digit of the prefix is dialled ; is suppressed.
after receipt of the second dialling tone (from
the distant tie line), the remaining two (or POWER PLANT
three) digits are sent. Since reliability is of paramount importance,
In Fig. 2, the heavy lines indicate an all P.A.B.X.’s are provided with a storage
established connection between station “A” battery, trickle charged from a selenium
in Antwerp and station “B” in Ostend. In this rectifier. There is, consequently, no danger of
case, when “A” temoves the receiver, he service interruptions due to mains supply
receives dialling tone from his local link and failure.
dials “7.” The tie line finder hunts for and The 50 cycle signalling power supply is
taken from the public lighting network. A 50
cycle reserve generator forms part of each
installation.
Each P.A.B.X. is provided with a 50 cycle
vibrator, which is operated from the P.A.B.X.
battery and which is automatically cut into
service if the mains supply fails.
TELEPRINTER SERVICE
Associated with each P.A.B.X. is a voice-
frequency operated teleprinter for the trans-
mission of service reports. Teleprinter service
~ BRUSSELS is established between any two P.A.B.X.’s by
first dialling the number of the Telex operator
and then switching over to the printer.
The circuits also are arranged in a manner
such that the teleprinter at any P.A.B.X. can
intercommunicate with teleprinters at the
Direction for Air Transport in Brussels via the
Fig. 3—Tie Lines. city junctions and the regular toll lines.
ELECTRICAL COMMUNICATION 237
CLARENCE HUNGERFORD MACKAY (1874-1938)
LARENCE HUNGERFORD MACKAY, Chair- becoming the first communications service in the
man of the Board of Directors of the Postal world to operate radio, cables and telegraph lines
Telegraph and Cable Corporation, President of the under one management.
Commercial Cable-Postal Telegraph System, and a Mr. Mackay’s interests outside his business
director of the International Telephone and Tele- activities were very diverse. A keen sportsman and an
gtaph Corporation, died exceptionally fine shot,
on November 12th, aged he had over sixty cups
64 years. and trophies to his
The son of the late credit.
John W. Mackay who Reputed to have one
in collaboration with of the world’s finest
James Gordon Bennett private collections of
entered the _ electrical armour, he also had
communications field an outstanding collec-
in 1883 by laying tion of pictures,
cables across the Atlantic tapestries and rugs.
in competition with the He was a director of the
powerful Jay Gould Metropolitan Opera
group and who in 1886 Company, trustee of
established the Postal the Metropolitan
Telegraph Cable Com- Museum of Art, and
pany, he became Chairman of the
President of the Mackay Philharmonic-
System of telegraphs Symphony Society of
and cables on the death New York. It was
of his father. in 1902. under his wise guidance
His contributions to that the Philharmonic
progress in the world Orchestra won its unique
of electrical communications included the comple- place in the world of music.
tion of the first trans-Pacific cable between the Among his many public services were his active
United States and the Far East in 1904, and the first interest in hospitalization work, and gifts aggregating
New York-Cuba cable in 1907. During the same $2 000 000 for educational purposes, including the
period, the Mackay System consolidated its position erection and maintenance of the University of Nevada
in the Atlantic by contracts with the German Cable —Mackay School of Mines, a memorial to his father.
Company, operating between New York and Emden, Mr. Mackay received numerous decorations, among
and by laying two additional cables, one connecting which were : Officer of the French Legion of Honour ;
with the Azores, and so serving Southern Europe ; the Knight Commander of St. Gregory; Commander
other linking New York and Ireland, serving Great of the Order of the Crown of Italy ; Cross of Knight
Britain and Northern Europe. Commander of the Order of the Crown of Belgium ;
In 1928, negotiations between .the Mackay and Officer of the Order of Orange Nassau of Nether-
Companies and the International Telephone and lands. His name will long be remembered, not only
Telegraph Corporation resulted in a merger of the for his business and civic activities, but also for his
Mackay System with the International System. In generous support of the arts and sciences through
the previous year the Mackay interests had acquired which he made important contributions to cultural
operating rights in the Federal Radio Company, thus development.
Proceedings of the International Telephone Consultative
Committee (C.C.LF.)
COPENHAGEN, JUNE 11th-20th, 1936.
English: Edition.
N line with previous practice* the Part V. Composition of the Commis.
| International Standard Electric Corpora- sions of Rapporteurs of th«
tion has published an English translation C.C.LF.
of the proceedings of the XI Plenary Meeting Part VI. List of C.C.I.F. Recommenda-
of the C.C.I.F. held at Copenhagen, June 11th- tions in force on January Ist
20th, 1936. The form of the present translation 1937,
differs from that of former years in that, for the APPENDIX. Summary of Principal Recom-
most part, only changes in and additions to mendations made by the 3rd
the previous (1934) volume, resulting from the 4th and Sth C.R.’s at thei
1936 Copenhagen decisions, have been included, meeting in Oslo, June 20th tc
Since a large portion of the recommendations July 2nd, 1938.
and information contained in the 1934 edition INDEX.
still remains in force, it was thought best to An important feature of the new edition is the
deal solely with new or modified material. Thus index, which has been enlarged and revised tc
changes in existing recommendations are clearly cover all material in the 1934 as well as in the
indicated. 1936 edition. The new index co-ordinate:
both volumes, indicating where recommenda-
The present volume comprises 388 quarto
tions and information may be found in both the
pages, uniform in format with previous volumes,
English and French editions, also whethe:
and includes the following sections :
material is new, modified or maintainec
GENERAL. unchanged.
Part I. Protection. Owing to the large demand, the customary
Part II. Transmission and Maintenance. nominal charge, to cover the cost of production
Part III. Operating and Tariffs. will be made for copies of the new edition.
Part IV. List of Questions set for study Requests for copies should be addressed to the
by the XI Plenary Meeting. International Standard Electric Corporation,
Connaught House, Aldwych, London, W.C.2.
or 67, Broad Street, New York City. A limited
*“ Proceedings of the International Consultative
Committee on Long Distance Telephony,”
number of copies of the 1934 edition can alsc
Electrical
Communication, October 1932, July 1933 and April 1936, be supplied.
238
Transmission Testing Apparatus
for 30-10000 p:s Communication Systems
By R. E. HERRICK, B.Sc., and H. MELLING, B.Sc., B.Eng.,
Standard Telephones and Cables, Limited, London, England
10 INTRODUCTION to the apparatus developed for one class of
test. This arrangement was chosen because
PAPER! presented before the
the same general development problems are
Institution of Electrical Engineers in
encountered regardless of whether the apparatus
. March 1924 dealt with the then
is intended for factory testing, for installation
contemporary aspects of the telephone mainten-
and. initial testing of the cable and associated
ance and testing problem, and discussed in
repeater stations, or for routine maintenance of
some detail the planning, economic, engineer-
the system after it has been put into service.
ing and theoretical questions involved. It is
It is not proposed to deal with testing equip-
interesting to note that, in general, the tests
ment especially developed for use during
cited still apply on voice frequency long
manufacture, but the whole ground of installa-
distance systems, indicating the soundness and
tion and initial testing of a system, as well as-
far-sightedness of the work done up to that
service routine testing, will be covered.
time.
The purpose of the present article is to 2.0 INSTALLATION AND MAINTENANCE
outline, from the European viewpoint, develop- TESTS
ments in apparatus design and testing methods
during the past fifteen years, including a brief The following tests must be made either
exposition of the situation at the beginning of during the installation of a system (as part of
the period. the installation procedure) or after completion
The description deals mainly with voice and of the installation as acceptance tests, in order
broadcast frequency testing equipment, the to ensure satisfactory overall quality of the
primary reason being that testing methods and completed system. For the proper maintenance
design have now to a considerable extent been of a system, some of these tests must be made
rationalized and stabilized for frequencies of at regular intervals on a routine basis.
30-10 000 p:s. It is planned in a sub-
sequent article to consider in more detail the 2.1 Capacity Unbalance and Capacity Devia-
tion Measurements
situation pertaining to measurements at higher
frequencies. During installation of a cable, the cable pairs
_ Controversial questions involving mainten- at the various cable joints must be connected
ance methods, organization and the economics so that the capacity unbalances between the pairs
of the problem are not discussed. They, how- produce a minimum of crosstalk.
ever, are important factors which have guided It is thus necessary to make a very large
the lines along which development. has pro- number of capacity unbalance measurements
ceeded. between the various cable pairs and between
It seemed advantageous to subdivide the the cable pairs and sheath before making the
article into sections corresponding, respectively, joints. Capacity deviation measurements also
are required to ensure that the mutual capacity
1“ Transmission Maintenance of Telephone Systems,” by of all the circuits in the cable is sufficiently
P. E. Erikson and R. A. Mack. Journal of The Institution
of Electrical Engineers, 1924, Vol. 62, No. 332. close to the mean mutual capacity. As any
239
240 ELECTRICAL COMMUNICATION
to measure at regular
intervals the trans-
mission efficiency of
each circuit and to
check the specified
performance. Con-
sequently, transmis-
sion measuring
equipment is installed.
in each repeater
station.
2.4 Measurement of
Cable Impedance
To guard against
faults which may
; occur in the laying
Fig. 2—74100-A loadi f bl
Auxiliary Condenser or oading of Cable,
Box, it is mecessary to
determine whether
the characteristic im-
pedance of the cable
and the — specified
Fig. 1—74100-A Capacity Unbalance Set. requirements are
met.
large capacity deviations critically affect the 2.3 Measurements of Impedance Unbalance
singing point of the repeaters, it is important
that the limits of deviation imposed be properly When two-wire circuits are converted to
met. four-wire circuits for the purpose of repeatering,
or when four-wire cable circuits are converted
2.2 Crosstalk Measurements to two-wire switchboard circuits, the necessary
hybrid coil may be the cause of singing round
The cable having been installed, crosstalk the four-wire circuit.
measurements between the various cable cir- The performance of the hybrid coil is to a
cuits, physical or phantom, are required in large extent controlled by the degree of imped-
order to make certain that interference to ance matching which can be achieved between
conversations due to crosstalk will be negligible. the two-wire circuit and an associated network
Similar tests in the various repeater stations connected with the coil. Apparatus must be
also are necessary to ensure that the cabling provided for this determination.
and apparatus do not cause crosstalk of a
serious order. 2.6 Noise Measurement
2.3 Measurements of Transmission Efficiency Apparatus for checking freedom from inter-
ference other than crosstalk between the
It is essential that the cable and associated telephone circuits is essential. Such interfer-
repeaters, networks and kindred apparatus ence may be caused by close association of the
provide the desired performance both as to cable with electric power circuits, electric
power transference and frequency char- railways, etc., or it may be introduced from the
acteristics. For maintenance purposes, it is usual repeater station power supply circuits.
TRANSMISSION TESTING APPARATUS 241
3.0 APPARATUS FOR INSTALLATION The Unbalance Set measures unbalances
AND MAINTENANCE TESTING with an accuracy of + 2 pyF, and the actual
unbalance measurable is + 1900 ppF. Capacity
The following seven subdivisions outline the deviation measurements may be carried out to
development situation on certain sets, produced an accuracy of + 50 pyF.
during the period under review for installation Both these sets were developed as a result of
and maintenance measurement purposes. In accumulated field experience, and have been
view of the fact that the modern transmission designed to combine speed and accuracy of
measuring set has a very wide range of applica- , measurement with minimum re-clipping of the
tion in connection with both initial system and test leads on the actual wires of the cable.
maintenance tests, it seems appropriate to The 74100 type Oscillator, which is com-
devote the major part of the present article to pletely self-contained, has been specially
consideration of this class of equipment. designed for use with these sets. It is a single
frequency oscillator with two low current con-
3.1 Capacity Unbalance sumption tubes arranged in push-pull, and
possesses output and output impedance char-
To facilitate capacity unbalance measure-
acteristics suitable for the efficient operation of
ments, two special portable sets of robust
the sets under all conditions.
construction have been evolved: the 74100
type Capacity Unbalance Set, and the 74100 3.2 Crosstalk Sets
type Auxiliary Condenser Box (Figs. 1 and 2). The measurement of crosstalk is funda-
The Capacity Unbalance Set consists mentally one of attenuation measurement, i.e.,
essentially of a retardation coil ratio arm bridge determination of the ratio of the power in the
and a differential air condenser. Suitable disturbed to the disturbing circuit. It might
switching facilities enable capacity unbalance be expected, therefore, that some similarity of
between side to side, phantom to side, side to method would exist between crosstalk and
earth, and phantom to earth circuits of a cable attenuation measurements. Such indeed was
quad to be determined directly. the case initially, the substitution method of
The Auxiliary Condenser Box is used in measurement being common to both. The
conjunction with the Capacity Unbalance Set trend of crosstalk measurement, however, has
and enables the capacity deviation of the pair not been so much towards increased accuracy
and phantom circuits from a standard capacity but, rather, towards maintaining the accuracy
(predetermined by the operator) to be measured of the original substitution method (well
directly on the differential condenser of the illustrated in the 74050-—A Crosstalk Set) over
Capacity Unbalance Set. a wider attenuation and frequency range.
Fig. 3—74101-A Crosstalk Set, Amplifier, PH-S Unit and Terminating Unit.
242 ELECTRICAL COMMUNICATION
A decade ago toll cable practice called for a sufficient gain to give a meter reading. The
crosstalk set capable of measuring crosstalk 74102-A Crosstalk Detector Amplifier was
down to 10 Crosstalk Units, equivalent to accordingly developed. By the operation of
100 db. attenuation. The set in general use a key, it can be utilized in three distinct
for such measurements was the 74050-A ways:
Crosstalk Set. Utilizing the substitution method, (a) As a flat amplifier (200-3 000 p:s) for
the observer listened alternately to the cross-. measurements with a complex testing
talk tone and the disturbing tone, the latter tone, e.g. the human voice or some
being heard via a variable attenuator calibrated special buzzer such as the 74020-—C
in crosstalk units. The attenuator was adjusted Test Set, which gives crosstalk results
until the two tones were judged to be of equal closely approximating to those obtained
loudness, the reading of the attenuator being with the voice.
the magnitude of the crosstalk. ‘The set
included a balanced retardation coil for measure-
(6) As a tuned amplifier capable of being
tuned to any frequency between 500 p:s
ment of phantom to side crosstalk. The and 2500 p:s, thus enabling unwanted
limitation of accuracy was obviously set by the line noises to be rejected.
subjective nature of the method, while the (c) As a detector amplifier for carrier
minimum value of 10 crosstalk units was frequency measurements.
determined by the sensitivity of the telephone
In order to obtain high accuracy with the
receiver and the observer’s ear. Carrying out
74101 type crosstalk set at the high attenua-
measurements in noisy locations also presented
tions involved, the circuit was made as simple
difficulties.
as possible; no facilities, therefore, were
With improvements in cable technique,
included for phantom to side crosstalk measure-
particularly the introduction of screened broad-
ments. A separate unit was developed for
cast pairs, the demand arose for a crosstalk set
phantom to side measurements in conjunction
capable of measuring pair-to-pair crosstalk
with the side to side crosstalk set. This unit,
down to a fraction of a crosstalk unit, and
which has a high degree of balance, is coded as
incorporating means for visual rather than aural
the 74101-A Phantom to side unit.
balance of the disturbing and the crosstalk tone.
The above group of modern voice frequency
Such a set involved an attenuation measurement
crosstalk measuring apparatus was completed
of 126 db. on balanced circuits, and the prob-
by the design of the 74101-A Terminating
lem was further complicated by the presence
Unit, suitable for terminating the circuits
on most cable pairs of transverse and longi-
under test. Fig. 3 shows the complete kit.
tudinal noise voltages of a magnitude seriously
interfering with measurement of fractional
crosstalk units: The new set, developed and 3.3 Transmission Measuring Sets
coded as the 74101 type Crosstalk Set (Fig. 3)
The apparatus provided. for this purpose
provides for crosstalk measurements over a
consists essentially of a source of A.C. tone
range of 7000-0.5 crosstalk units (approx. 43-
which is transmitted into the cable or apparatus
126 db.), at any frequency between 200 p:s
and 25 ke/s. to be measured, and a transmission measuring
set to measure the power level at various points
This set retains the substitution method
on the system. For routine maintenance
which, for measurement of high attenuation, is
measurements such apparatus is ordinarily
still the simplest and the most accurate.
included in the test rack equipment in each
Naturally, crosstalk measurements as low as
repeater station whilst, for installation and fault
0.5 crosstalk units would not be possible with-
diagnosing, additional apparatus in portable
out a high gain amplifier, inasmuch as the
form is usually desirable.
extremely weak crosstalk currents must be
raised to levels capable of being heard in a (a) Early Sets
telephone receiver. Further, where visual Typical apparatus, prior to 1924, consisted
indication is required, the amplifier must have of the 74002 type Oscillator and the 74001
TRANSMISSION TESTING APPARATUS 243
type Transmission Measuring Set. They were
designed for measuring line and exchange
losses at a single 1000 p:s frequency. ‘The
oscillator included a carbon microphone coupled
to a receiver by a tuned bar, whilst the trans-
mission measuring set was of the substitution
type in which the circuit under test and a
variable attenuator were switched in turn
between the oscillator and a head receiver.
The attenuator was adjusted until the tone
heard in the receiver was equal to the tone
heard when the line under test was connected
in circuit. The reading of the attenuator then
indicated the loss in the circuit under test.
The accuracy of this combination was
limited by the poor waveform of the oscillator : Fig. 4—74022-A Level Measuring Panel and 74021-A
and the sensitiveness of the ear of the tester at Oscillator.
various power levels, the latter being important
because of the low power levels at which the connecting the circuit under test (into which a
apparatus must be used. It was also restricted 1 milliwatt tone was sent) to the amplifier, and
in its range by the fact that it was a single adjusting the overall gain by means of the
frequency device, and was not suitable for calibrated attenuator until the D.C. meter again
attenuation measurements on looped circuits. gave the predetermined deflection. Hence the
It was, furthermore, a low impedance device circuit attenuation was indicated by the reading
adaptable only to “‘loss’? measurements, its of the calibrated attenuator.
design precluding the taking of “‘level’”’ measure- In addition to the advantage of visual as
ments at various points on a toll cable circuit. compared with aural indication, this new
combination represented a marked advance as
(b) Use of the Thermocouple and Thermionic regards increased accuracy in making measure-
Valve ments, adaptability to obtaining readings at
A great advance in the design of transmission low levels, and the facility of conducting tests
measuring apparatus was achieved by the use at predetermined levels.
of the then recently developed vacuum tube, Originally these sets were designed to operate
and the application of the thermocouple from 24-volt exchange batteries, and the
junction. The oscillator then became a valve- 74003 Type ‘Transmission Measuring Set
operated device with greatly improved wave- enabled equivalents as low as 30 db. (the set was
form and stability of frequency and output, calibrated in miles of standard cable) below
whilst the measuring panel took the form of an 1 milliwatt to be measured. This set was,
A.C. valve-amplifier followed by a _ valve- however, still restricted to single or narrow
rectifier operating a sensitive D.C. micro- band frequency measurements.
ammeter. It was possible, furthermore, by With the advent of valve repeaters it became
means of the thermocouple, to check the level both necessary and advantageous to design sets
at which the testing power was sent into the operating from 130-volt and 24-volt repeater
circuit, and a standard sending level of 1 milli- station batteries, whilst improvements in coil
watt was adopted. This sending circuit was design made it possible to extend the voice
also used to calibrate the amplifier-rectifier, frequency measuring range over 200 to 3000
the gain being adjusted for a certain pre- p:s. It was necessary, owing to variation in
determined deflection of the D.C. meter. The oscillator output and amplifier gain with
amplifier was preceded by a calibrated attenuator frequency, to make calibration adjustments at
which altered the overall gain by a known each frequency. Sets were then manufactured
quantity. Measurement was carried out by for installation in the test position of each
244 ELECTRICAL COMMUNICATION
repeater station. The 74004 type Transmission of a toll circuit could thus be checked simul-
Measuring Set (which included numerous taneously at all repeater stations throughout the
switching facilities) marked the stage where cable length by sending standard power into
this type of apparatus was installed in repeater one end of the circuit and bridging a trans-
stations and used for maintenance purposes. mission measuring set across the line at each
At the same time special sets were developed repeater station.
for measuring repeater gains, the 74002—A and It was, however, necessary to carry out
74003-A Gain Sets being typical examples. calibration adjustments at each frequency;
They operated on the substitution principle, an hence, though achieving highly accurate per-
attenuator being inserted in front of the formance, the time occupied in taking a number
repeater and its reading adjusted until the of frequency runs was still a serious factor.
transmission equivalent of the circuit equalled For special measurements, installation and
that in the calibrated position. Measurement acceptance test work, transportable counterparts
was generally made with a 1000 p:s valve of these two sets were used—the 74008—A
oscillator and the detecting device usually was Oscillator and the 74100 type Transmission
a thermocouple or an amplifier detector, Measuring Set. The latter was particularly
although in some circumstances the telephone adapted to measurement work on toll cables.
receiver still continued to be employed.
The introduction of broadcast circuits made (c) Direct Reading Sets
it necessary to extend the frequency range of As toll circuits multiplied and the number of
the apparatus over 30 to 10 000 p:s. Improve- repeaters in the stations increased, speed of
ments in coil and circuit design enabled the testing became more and more important,
amplifiers, oscillators and sending circuits to especially for routine measurements. With the
be suitably modified. then existing sets the number of adjustments
The culmination of this phase of develop- on the oscillator for each frequency setting
ment was reached with the 74006 type Trans- might be as many as six or seven, whilst the
mission Measuring Set and the 74010-B transmission measuring set required three
Oscillator. These were sets of very high adjustments, i.e., calibration of the oscillator
performance, and were adopted as standard for sending purposes, and adjustments (two) in
equipments for routine maintenance measure- connection with the amplifier calibration.
ments. They may be seen side by side in a Measurements were consequently slow and
great number of repeater stations throughout laborious, especially where frequency runs had
the world. The measuring set offered facilities to be made, whilst extreme accuracy of measure-
for transmission measurements over the range ment achieved by these sets was not always
+ 20 db. to- 30 db. referred to 1 mW, special necessary.
provision being included for the measurement Clearly, for the rapidly growing number of
of repeater gains and for talking and setting up necessary routine measurements, testing equip-
measuring circuits in repeater stations. The ment both simple and rapid in operation was
accuracy of measurement was + 0.2 db. over required, though not necessarily highly accurate
the frequency range 30 to 10000 p:s and in performance. ‘To meet this demand, the
+ 0.1 db. from 200 to 3000 p:s. The oscillator 74021 type Oscillator and 74022 type Level
was extremely stable and was very closely and Measuring Panel were developed (Fig. 4). The
accurately calibrated over the whole frequency oscillator was designed to give seven fixed
range, thus providing means for precise measure- frequencies (spaced throughout the voice
ments in the region of the cut-off frequency of frequency spectrum from 200 to 3000 p:s) by
cable and filter circuits. the simple operation of a key. This eliminated
It was also possible to make voltage or “‘level”’ the necessity for a calibration chart and numer-
measurements by designing the amplifier of the ous dial settings for each frequency; and,
transmission measuring set with a high input whilst the oscillator did not have exactly con-
impedance so that it consumed negligible power stant output with frequency, the outputs were
from the circuit under test. The performance sufficiently level (within about 2.0 db.) to enable
TRANSMISSION TESTING APPARATUS 245
the level measuring set to be easily operated. adequate for routine measurements. The panels
Setting the oscillator was therefore greatly also were smaller and simpler, while the space
expedited, while the performance, though not occupied and the cost of the equipment was
as good from the viewpoint of frequency considerably reduced.
stability and flexibility as the 74010 type, was The advent of these direct reading sets was
adequate for its purpose. brought about by the following developments
The 74022 type Level Measuring Panel in technique :
represents the beginning of a further stage of (1) Improved coils, enabling amplifiers with
measuring set development and was the first a very flat characteristic to be developed.
“direct reading” transmission measuring set The modern feed-back amplifier, of
to be produced. By this is meant that it was course, has made possible further
the first set to have the indicating meter improvements in this direction.
calibrated directly in decibels or nepers, and Production of “shaped pole”’ meters
requiring calibration at a single frequency only. in which the current deflection law is
It also incorporated a metal rectifier in place of such that an approximately evenly
a thermocouple for sending purposes, thus divided decibel or neper scale can be
further obviating calibration. The operation of achieved.
this set, therefore, was extremely simple, Application of the metal rectifier meter, a
calibration adjustments at different frequencies useful instrument for the measurement
not being required. The set covered the of alternating currents. Though not so
frequency range 200 p:s to 3000 p:s and accurate, and possessing inherent dis-
measured levels from + 15 db. to — 35 db. advantages, due to the temperature co-
referred to 1 mW with an accuracy of + 0.5 db. efficient and self capacity of the rectifier,
This combination increased the speed of it was found possible to substitute it for
maintenance measurements tenfold and, al- the thermocouple junction in voice
though the performance was not as precise as frequency measurements of this nature.
that of the 74006 type Transmission Measuring The three main disadvantages of the
Set and 74010-B Oscillator, it was found to be thermocouple, viz., fragility, delicacy
Fig. 5—74101-B Oscillator. Fig. 6—74101-N Transmission
Measuring Set.
246 ELECTRICAL COMMUNICATION
and expensiveness of the associated were instantly appreciated and they began to
direct current meter, and the necessity be used under all circumstances where speed
for direct current calibration, were over- of operation justified the sacrifice of extreme
come by the use of the rectifier although, accuracy.
as previously stated, the latter intro- Sets similar in circuit and performance were
duced errors of its own. It was found, then designed for rack mounting, viz., the
however, to be satisfactory for certain 74201-A Heterodyne Oscillator and 74201
types of transmission measuring equip- type Transmission Measuring Set. They are
ment; and, as development proceeded, being used as a standard in smaller repeater
it became possible, by careful circuit stations where apparatus of greater precision
design, to extend its use over the whole and higher cost is not economically justified.
voice frequency range up to 10000 p:s The transmission measuring set includes means
without introducing serious errors. for sending constant voltage for lining up broad-
The success of the direct reading combination cast circuits, and also low level sending facilities
was so marked that it was clearly necessary to for measuring repeater gains.
proceed further with the development of sets The next step was the production of two sets
of this type. The next combination to appear of precision sufficient to warrant their use in
was the 74101 type Heterodyne Oscillator large repeater station for more accurate work,
(Fig. 5) and the 74101 type Transmission whilst retaining the simplicity of operation of the
Measuring Set (Fig. 6). The Heterodyne direct reading feature. These sets, the 74102-A
Oscillator introduced further simplification in Heterodyne Oscillator (Fig. 7) and the 74102
operation since it incorporated a single dial type Transmission Measuring Set (Fig. 8), have
engraved directly in frequency, enabling all been installed in a number of major repeater
frequencies in the 30 to 10 000 p:s band to be stations in Europe with very satisfactory results.
obtained with an accuracy of + (2% +2 p:s). A brief summary of their specifications and
It also had an output constant within 0.25 db. method of operation will serve to indicate the
over the entire frequency range, and was thus level which the design of direct reading trans-
suitable for measuring frequency characteristics mission measuring equipment has reached.
without alteration of the sending adjustment.
The transmission measuring set was similar in 74102-A Heterodyne Oscillator
design to the 74022 type, employing a constant Output : 0.3 W into 600 ohms. Constant with
gain amplifier, a metal rectifier, and a “shaped frequency to within + 0.1 db.
pole” meter engraved direct in decibels or Harmonic Content : Less than 2%.
nepers. It covered the range 30 to 10000 p:s, Frequency Range : 30-10 000 p:s.
measuring from + 15 db. to —45 db. referred Accuracy of Frequency : + (2% +2 p:s).
to one milliwatt with an accuracy of + 0.25 db. Scale Law: Linear to 100 p:s. Logarithmic
The apparatus was in portable form and was 100 p:s to 10000 p:s.
the first measuring combination of any accuracy The scale is engraved on a dial of a specially
to be really light and suitable for transportation designed high grade condenser. This latter
from station to station. It also had the advan- forms the tuning element of one of two high
tage of covering broadcast circuit requirements. frequency oscillators operating at a nominal
The simplicity and speed of operation of this frequency of 100 kc/s. These two oscillators
pair of sets were of course in advance of any of are jointly modulated by means of a double-
the preceding sets. A frequency-level char- balanced metal rectifier circuit, and the voice
acteristic could be obtained by merely rotating frequency output is applied to a push-pull
the dial of the heterodyne oscillator through the amplifier producing the necessary output level.
required frequency range and noting the
reading of the meter of the measuring set. 74102-A Transmission Measuring Set
Despite the fact that the accuracy was inferior Sending Facilities: The set when used with the
to that of the highly precise 74006 type above oscillator delivers the following power
Measuring Set, the advantages of the new sets levels :
TRANSMISSION TESTING APPARATUS 247
(a) 1 milliwatt,-—10 to-—50 db. referred to run. ‘The sending circuit employs a metal
1 mW in steps of 10 db., into a 600 ohm rectifier meter to indicate the power level; by
circuit from an internal impedance of suitable circuit design, this meter has been
600 ohms ; found to give results nearly as good as the
thermocouple. It requires no preliminary
(5) 0.775, 1.55, 2.1 and 4.0 volts from a low
direct current calibration.
internal impedance (constant voltage
sending) into a 600 ohm circuit. A comparison of the adjustments necessary
with this combination and with the 74010
_ The accuracy of the sending level is ++ 0.2 db.
over the frequency range 30 to 10 000 p:s. type Oscillator and 74006 type Transmission
Measuring Set serves to indicate the simplicity
Receiving Facilities: "The set measures levels and speed of operation attained. (See Table I.)
between + 25 and -50 db. referred to 0.775 volt It must be borne in mind that the absolute
over the frequency range 30 to 10000 p:s.. A600 accuracy of the old type of set has still not been
ohm termination is provided for use when it is achieved in these new sets; and, in particular,
required to measure transmission equivalents. the 74102-A Heterodyne Oscillator does not
‘The accuracy is + 0.2 db. over the whole compete with the 74010 type Oscillator where
frequency range and is considerably greater frequency, accuracy and stability are of the
when measurements are carried out at 1 000 p:s. greatest importance. Experience has shown,
The set is equipped with a direct reading however, for the great majority of toll system
meter covering a range of 15 decibels, the meter measurements, that the accuracy of the new
having shaped poles to give an evenly divided equipment is ample, whilst the facility of taking
scale, whilst the amplifier has a flat frequency a frequency characteristic by simply rotating
characteristic so that calibration is necessary at the oscillator condenser dial and reading the
one frequency only before taking a frequency meter of the transmission measuring set has
TABLE I.—COMPARISON OF ADJUSTMENTS
Oscillator
74010 (older type) 74102 (newer type)
{ Zero beat calibration (setting of one
Pradjusnnent | Nil dial). ——
Setting of i | Adjustment of Feedback re- Rotation of one dial until correct
Frequency sistance, four condenser reading is noted.
t dials, and a switch from a
calibration chart.
Control of Out- Adjustment of dial at each No adjustment necessary if constant
put. frequency. output required at each frequency,
after initial adjustment of one knob.
Transmission Measuring Set
74006 (older type) 74102 (newer type) ;
SENDING. Two preliminary adjustments Adjustment of one knob at initial
for calibration of thermo- frequency setting only.
couple and adjustment of
one knob at each frequency.
RECEIVING
(a) Calibration. Throwing of key and adjust- Throwing of key and adjustment of
ment of one dial at each one control at a single frequency only.
frequency.
(6) Measurement. Throwing of key and adjust- Reading indicated directly on the decibel
ment of one dial at each (or neper) meter unless levels vary by
frequency. more than 15 db., when one dial has
to be operated.
248 ELECTRICAL COMMUNICATION
Fig. 8—74102-A Transmission Measuring Set.
Fig. 7—74102-A_ Oscillator.
proved to be a very great labour-saving and, the completed recorder the vertical time lines
therefore, an economic advantage. of the chart are engraved in frequencies
corresponding to those transmitted by the
(d) Automatic Level Recorders oscillator, and the horizontal lines are engraved
The logical development of these advan- in decibels or nepers to correspond with the
tageous direct reading sets was the recording readings of the transmission measuring set
of frequency characteristics automatically on a meter.
chart, thus eliminating any necessity for taking The 74102 type Automatic Level Recorder
and recording columns of readings. This (Fig. 9) is designed to provide these facilities
facility is of particular importance when lining and is built around the 74102-A Heterodyne
up international cable circuits since it enables Oscillator and 74102 type Transmission
a record of the circuit performance to be taken Measuring Set. It is mounted on two racks,
at the frontier of each transit country, and forms one containing the sending and the other the
concrete evidence of the condition of the circuit receiving equipment, and is arranged to operate
in the domain of each Administration. from the normal repeater station batteries.
From the facilities offered by the Heterodyne The Heterodyne Oscillator is mounted on
Oscillator and the direct reading type Trans- the sending bay immediately below the 74102-A
mission Measuring Set it will be clear that, if Driving Panel. The latter includes a governor-
the oscillator frequency condenser is mechanic- controlled electric motor for driving the oscil-
ally driven, and the movement of the receiving lator condenser, together with suitable relay
meter is simulated on a recording meter with equipment.
a chart moving in synchronism with the speed On the receiving bay is fitted the Trans-
of the condenser, it will be possible to record mission Measuring Set and, immediately above,
on the chart of the latter meter the frequency- the 74102-A Recorder Amplifier panel, which
level response characteristic of any circuit. In contains the recording meter, together with a
TRANSMISSION TESTING APPARATUS 249
suitable amplifier for repeating the reading of large repeater stations in Europe and have been
the transmission measuring set meter. found to greatly speed up the routine mainten-
To conform with the standardized require- ance of the toll and broadcast circuits.
ments of the C.C.I.F., laid down to ensure inter-
working, the speed of the electric motor driving (e) Mains-Operated Sets
the oscillator condenser, and the clockwork The present trend in the operation of repeater
motor driving the recording meter chart, are
synchronized so that the time to run from zero
frequency to 10000 p:s-is 121.2 seconds.
The precise C.C.I.F. requirements relating to
the frequency time scale law have also been
achieved.
The apparatus is arranged so that the sending
equipment may be located at one terminal and
recelving equipments at the principal stations
along the cable. The sending equipment then
controls the taking of a record; arrangements
are such that, when the oscillator condenser
passes the zero frequency mark, .a signal of
1300 p:s and of 1.5 seconds duration is
transmitted along the line under measurement.
This signal trips relays in the circuits of each
receiving equipment and starts the recording
meters, thus ensuring that they are in syn-
chronism with the oscillator condenser.
Single button starting and automatic restora-
tion at the completion of a record are employed.
The total time required for taking a complete
record and restoring the level recorder to rest
is 3 minutes. When this time is compared with
that required with the old step-by-step method,
the great advantage of the instrument in busy
stations will be appreciated.
Quite apart from the advantages of speed
and the provision of comprehensive and per-
manent records of line characteristics, the new
method tends to reduce conversation between
repeater stations on the circuits under test.
This apparatus is accurate to approximately
+ 0.5 db.—sufficient for most routine measure-
ments—and is arranged so that it may be
operated manually to give improved accuracy
when desired.
An additional panel equipped on the sending
rack enables singing point frequency char-
acteristics to be taken when required (see section
3.5), whilst the Level Recorder is equipped
with a suitable telephone panel, link panel and
battery supply circuit for making easy connec-
tions to circuits.
These sets are installed in a number of the Fig. 9—74102-A Automatic Level Recorder.
250 ELECTRICAL COMMUNICATION
stations is towards the use of high voltage A.C. set, coded the 74101-A Sending and Impedance
mains rather than accumulator batteries. ‘To Unbalance Unit, however, is supplied; it pro-
meet these conditions, two mains-operated sets vides for sending 1 mW, low levels for gain
have been produced, the 74104 type Hetero- measurements, and constant voltages from low
dyne Oscillator (Fig. 10), and the 74109 type impedances. As explained in section 3.5, this
Transmission Measuring Set (Fig. 11). They unit also serves for making singing point
are the mains-operated counterparts of the measurements.
74101—A Heterodyne Oscillator and the 74101 Work is at present proceeding with the
type Transmission Measuring Set previously conversion of the 74102-A Automatic Level
described. In addition to providing the same Recorder, to enable the whole range of measur-
facilities as these sets, they are light and port- ing equipment to be available in mains-operated
able, and cover the frequency range of 30- form.
10000 p:s and the level range of + 25 to
3.4 Impedance Bridges
— 45 db. with an accuracy of + 0.25 db. These
sets are also being produced in rack mounted Two types of bridge have been developed for
form for small repeater stations. impedance measurements. ‘The earlier was
The 74109-A Transmission Measuring Set the 74001-B Impedance Bridge. It was a
does not provide sending facilities. A separate portable instrument built in three units, con-
sisting of an inducto-
meter, a resistance box
containing the ratio
arms, and a fixed air
cored inductance. The
design consisted of an
ordinary bridge circuit
with resistance ratio
arms. The measuring
arm contained the resist-
ance decade; and,
according to the angle
of the impedance to be
measured, the induct-
ance elements were
switched into either the
Fig. 10—-74104-A Heterodyne measuring or unknown
Oscillator. arm, thus enabling
positive or negative
angles to be measured.
In each case simul-
taneous switching of
resistances enables the
resistance of the in-
ductometer and fixed
inductance to be com-
pensated for. This
bridge gave direct in-
dication of the cable
impedance in terms of
series resistance and
Fig. 11—74109-A Transmission Measuring Set. series reactance. ‘The
frequency range covered
TRANSMISSION TESTING APPARATUS 251
was approximately 200 p:s to 2800 p:s with
anaccuracy at800 p:s of about + 1% on effective
resistance and + (1% + 0.001) henry on
effective reactance.
While fundamentally simple and easy to
operate, the bridge contained certain mechanical
and electrical deficiencies. The three units
were somewhat cumbersome and not particularly
well adapted to easy transportation. In addition,
the decreased accuracy at the top of the
frequency range hardly made it suitable for
measurements on modern loaded repeater
circuits. To meet more exacting requirements
a new type of bridge, the 74102-A Impedance
Bridge (Fig. 12), was introduced. This bridge
is built in a single unit and, being housed in a
solid teak box, is much more suitable for
transport than the older type. The ratio arms
are formed by a balanced hybrid coil, whilst
the measuring elements are resistance decades
accurate to + 0.1% and a capacity decade
accurate to 0.5%. These two elements are
arranged in parallel for negative angle measure-
Fig. 12—74102-A Impedance Bridge.
ments, whilst for positive angle measurements
the capacity decade is in parallel with the
unknown impedance.
impedances directly. Impedance unbalance is
The cable impedance is therefore measured
in terms of parallel resistance and reactance. Z4,4+ 2% ;
defined as 20 Log ———— decibels, where 2,
Greater accuracy and a wider frequency range 1— Ze
are attained as compared with the 74001-B type and Z, are the two impedances in question.
and the mechanical construction is more modern. The line and network to be tested may there-
The design is such that the calibrated con- fore be connected across the bridge arms of
denser decades, resistance decades, or hybrid the hybrid coil and the unbalance determined
coil may be disconnected and used for other by means of the amplifier.
purposes when desired.
2.. Measuring Sets
3.5 Impedance Unbalance Measuring Sets
A comparatively early set incorporating
1. Principle of Design these principles was the 74100 type Impedance
All these sets employ the well-known proper- Unbalance Measuring Set. This set contained
ties of the three-winding transformer or hybrid a suitable hybrid coil, a thermocouple sending
coil. A source of tone and an amplifying circuit for determining the level of tone applied
detector are connected to the coil in a manner to the coil, and an amplifier detector of adjust-
such that, when perfect balance obtains between able gain to measure the singing point. The
the impedances connected to the bridge arms detector was a valve rectifier followed by a
of the coil, no tone is transmitted to the amplifier. D.C. microammeter, and the amplifier was
If, however, the balance of the impedances is operated on the substitution principle in a
disturbed the amplifier receives. tone and it manner somewhat similar to the 74006 type
can be shown that, provided the coil input level Transmission Measuring Set, described in
of the source of tone is known, the output of section 3.3. Calibration was effected by
the amplifier, when calibrated, can be made to connecting a pair of resistance spools of known
measure the impedance unbalance of the two unbalance across the hybrid coil and adjusting
252 ELECTRICAL COMMUNICATION
the gain of the amplifier until the meter pointed prompted the omission of the impedanc
to a specified mark. The impedances to be matching switch since, when constant voltage i
measured were then connected to the hybrid applied to the hybrid coil, the voltage develope:
coil and the gain of the amplifier adjusted, by across the amplifier terminals is independent o
means of a dial engraved in decibels, until the the characteristic impedance of the circuit an
meter again gave the same reading. "The only dependent on the unbalance. Simultane
engraving on the dial then read the singing ously, the frequency range was extended t
point directly. This set covered the frequency cover 30 p:s to 10 000 p:s and the hybrid coi
range 200 to 3000 p:s and measured singing balance improved so that singing points up t:
points from 0 to 40 db. It required adjustment 55 db. could be measured. The 74102 typ
of the sending circuit and recalibration of the Impedance Unbalance Attachment, designe:
amplifier at each frequency and was heavy to for rack mounting and consisting of a simpl
transport and somewhat tedious to operate. panel 34” x19”, furnished these facilities. 1
The advent of the direct reading transmission was associated with the 74102 type Automati
measuring set opened up a field for a much Level Recorder and made possible singin
simpler set, for it was clear that the sending and point measurements and frequency-singing poin
receiving portions of such a set could be used characteristic recordings with the simplicit
for singing point measurements. provided an that now obtains on ordinary level and los
external hybrid coil was used. The 74101 type measurements.
Impedance Unbalance Attachment was there- For portable purposes the circuit was em
fore produced in 1935 for use with the 74101 bodied in the 74101 type Sending and Imped
type Transmission Measuring Set. The sending ance Unbalance Unit (Fig. 13), a set which wa
circuit of the transmission measuring set was designed for use with the portable 74101 0
used to send a known level into the coil, and 74109 type Transmission Measuring Sets.
the receiving circuit to read off the singing It will be noted that the development tren:
point directly in decibels or nepers. Calibration has resulted in the production of a very smal
of the receiving circuit of the transmission and cheap attachment, suitable for use in con
measuring set was performed by connecting junction with the modern direct reading trans
resistances of known unbalance across the coil mission measuring set and heterodyne oscillator
and adjusting the gain so that the transmission Thus both the cost has been reduced an
measuring set meter read the correct singing operation simplified.
point.
3.6 Noise Measuring Sets
This panel represented a great advance over
the 74100 type Impedance Unbalance Measur- Since noise present in a telephone circui
ing Set. It decreased the time of operation reduces the intelligibility of the conversation
inasmuch as all the advantages of the 74101 it is essential that every means be adopted t
Transmission Measuring Set, i.e., simple adjust- keep the noise level within reasonable limits
ment, direct reading and calibration at one This is achieved both by study of the interferin;
frequency only, were available. The size and sources, i.e., power lines, traction circuits
weight were radically reduced (from 100 Ib. telegraph circuits, faulty metallic contacts, etc.
for the 74100 Impedance Unbalance Set to and by investigation of methods for the reduc
18 Ib. for the 74101 type Impedance Unbalance tion of their interference with the communica
Attachment). This new panel covered the tion circuit. In order that the required in
frequency range 300 to 5000 p:s, measured telligibility may be attained, the tolerable nois:
singing points from 0 to 45 db., and was on any toll telephone circuit has now bee
provided with an impedance matching switch determined and limits imposed. For all thi
which enabled singing points to be measured work some simple, accurate, and portable forn
accurately over the impedance range 500 to of noise measuring set is indispensable.
3 000 ohms. Until recently no unit, which enabled th
In 1936 the necessity for providing constant noise level on a telephone circuit to be simph
voltage sending on transmission measuring sets stated, was in general use. However, when thi
TRANSMISSION TESTING APPARATUS 253
C.C.LF. definition of psophometric E.M.F.
was issued, and when the same body prepared
a specification for a line noise meter, or
psophometer, the art of noise measurement
took a considerable stride forward.
Previously noise measuring sets had been of
the subjective type, the observer adjusting some
“standard noise’ until, in his opinion, it was as
loud as the circuit noise. All sets based on this
method were subject to the personal errors of
the particular observer, a large number of tests
by different observers being required to render Toiteess,
poe
the result free of such errors. It should also MUS N ARO an ge
be noted that this method gave a measure of
the loudness and not the intelligibility reduction
factor of the noise.
The psophometer, as defined by the C.C.LF.,
departed from this subjective method and took
the objective form. It was an attempt to
produce an electrical system equivalent to the
complex acoustic-electric system of the human Fig, 13—-74101-A Sending and Impedance Unbalance
Unit.
ear and the telephone receiver. As such it
must of necessity remain a somewhat crude
approximation; nevertheless, providing its of this filter network is to ‘weight’? every
basic limitations are recognized, it forms a very frequency in accordance with its interference
valuable instrument and possesses the virtue value relative to 800 p:s. Such filter circuits
of giving adequately consistent results. are commonly referred to as Weighting Net-
The specification of the C.C.LF., stated in works, and the weighting factors of two such
general terms, calls for an instrument capable networks have been specified by the C.C.LF.
of measuring any psophometric voltage between One weighting network is intended for psopho-
the limits of 0.05 mV and 100 mV. The metric measurements upon commercial
psophometer consists of a calibrated valve volt- telephone circuits, and the other for similar
meter designed to meet special requirements, measurements upon circuits used for the
and should contain a filter network associated transmission of broadcast music.
with the measuring instrument. ‘The function The 74100-A Psophometer (Fig. 14) was
Fig. 14—74100-A Psophometer.
254 ELECTRICAL COMMUNICATION
developed to meet all the requirements of the heterodyne oscillator would be outside the
C.C.1.F. and to provide certain additional scope of the present article.
facilities. It seems desirable, nevertheless, to sketch
For ease of handling and maximum applica- the main considerations which govern the design
tion, the 74100-A Psophometer has been of these oscillators, and to attempt to give an
divided into two units. One unit is a calibrated indication of the problems involved.
valve voltmeter with a flat response from 50 p:s The fundamental characteristics of a modern
to 15000 p:s; the second unit contains filter oscillator would seem to be :
networks designed to give the C.C.I.F. weight-
ing for both telephone and broadcast circuits, (a) Frequency Stability
together with a battery noise circuit which Constancy of frequency at any setting.
permits noise measurements being made upon Calibrations, whether involving charts or
direct current circuits. An octave filter can engravings on dials, must have both long
also be used in place of the C.C.I.F. Weighting period and short period stability. This
Network. stability must hold under all reasonable
The measuring range at the psophometer is conditions of temperature and battery supply.
from 0.02 mV up to 1500 mV. An interesting Brief and totally inadequate mention of
feature is a self-contained calibration circuit factors such as the temperature co-efficient
whereby the amplifier gain is checked by a of coils and condensers in the oscillatory
feedback method. circuit, of the ageing of both, and of the
Owing to the high gains required, it is necessity for careful circuit design must
impossible to operate the valves in the set suffice to indicate the complexity of the
from noisy power mains, or from repeater problem.
station batteries. It is therefore essential that In the case of the heterodyne oscillator,
they should operate from small capacity port- further complications are involved by the fact
able batteries; the 74100-A Psophometer is that the utilized beating frequencies are often
suitably arranged for such operation. ten times greater than the maximum output
frequency; also, in level recorders, the
3.7 Oscillators frequency scales must follow closely defined
jaws and must be very accurately reproducible.
In the foregoing, particularly in section 3.3,
some indication has been given of the general (b) Constancy of Output
trend of oscillator design. Development pro-
gress has been traced from the pre-valve days The output must have good short period
of the buzzer type of oscillator, to the present stability under all conditions encountered in
time when the heterodyne oscillator with its practice and must, in addition, have a flat
direct frequency control on a single dial and its output frequency characteristic.
flat output characteristic is predominant in the Amplifier and modulator, as well as
field of voice frequency measurement. The oscillator, design are involved in this problem.
advantages of speed and simplicity of operation In the modern heterodyne oscillator, the
of this oscillator have been noted and general output variation from 30-10 000 p:s is often
comment has been made on its suitability for less than 0.1 db.
use with modern direct reading transmission
(c) Good Wave Form
measuring sets.
No mention has been made of the experi- The oscillator output must not contain a
mental and theoretical work which has been high percentage of harmonics of the frequency
done on general oscillator circuit design, since to be transmitted.
it was considered that any detailed description Amplifier and filter design and the
of the highly involved and often laborious consideration of levels throughout the circuit,
investigations which have contributed to the together with careful attention to the modu-
successful production of a stable and accurate lator, are the chief factors involved.
TRANSMISSION TESTING APPARATUS 255
CONCLUSION made in the art of Transmission Measurement.
As explained in the introduction to this No bibliography is appended to this article
article, it was the rather ambitious aim of the and space limitations prevent individual acknow-
authors to cover the whole ground of installa- ledgment amongst the great international family
tion and maintenance testing of Voice Frequency of research and development engineers who
Telephone Systems from the point of view of have contributed to the progress herein recorded.
apparatus design. It has unfortunately not Their names will be found in a multitude of
been possible to include detailed descriptions technical journals in almost every known
of individual sets or even to describe at any language. Since, however, the earlier sets in
great length the problems encountered during particular followed the general technique of
development. It is hoped, however, that the the Bell Telephone Laboratories, Inc., the
picture which has been presented will be of authors take pleasure in acknowledging the help
interest to telephone engineers and will convev and inspiration received from them, both
some impression of the progress which has been directly and indirectly.
Section of Bell Telephone Manufacturing Company (The Hague, Holland) exhibit at the Utrecht Fair,
7th-l6th September. Telephone Sets, small type P.A.B.X.’s, Railway Control Systems, Radio Receiving
Sets and Army and Navy radio equipment were featured.
Edinburgh-Aberdeen Cable
Special Construction Methods Used at the River Crossings
By H. BIRKBY,
Superintendent of Construction (External), Standayd Telephones and Cables, Limited, London, England
ROJECTS recently completed for the and further tested. These two lengths were then
Pp British Post Office include the jointed together and the cable from one drum
Edinburgh ~ Aberdeen 12 - channel coiled over the cable on the other drum, thus
carrier-on-cable system, covering a distance of forming a double length of approximately
approximately 123 miles and comprising two 640 yards on one drum. Each cable comprised
12 quad 40 Ib. cables. six such double lengths. Each two of these
The route crossed the River Tay at Dundee lengths were again subjected to tests and jointed
and The Firth of Forth at Queensferry. Inas- together, making three slings each approximately
much as a road bridge for the cables was not 1 280 yards in length, and these were finally
available at either of these places, interesting tested and jointed together.
installation problems were encountered. ‘The Each complete cable was finally coiled in one
means by which they were solved is described length on a large drum, the dimensions of which
briefly in this article. were :—
Body diameter 60 in.
RIVER TAY CROSSING Overall diameter 106 in.
Cable Manufacture Width between flanges AO in.
Since five subfluvial cables had previously Overall width 51 in.
been laid in the River Tay, it was decided in The conductors were jointed by means of
the present case to use a subfluvial cable. copper ferrules; the wire joint was insulated
The length specified for each “Go” and with the papers insulating the two conductors
“Return” cable was 1.87 miles with a total jointed together, the papers being tied in posi-
additional 0.5 mile of spare cable for mainten- tion. The wire joints were staggered over a
ance purposes. It was accordingly decided to length of 6 ft. Gin. The lead-antimony sleeve,
manufacture each cable 2.12 miles in length, when placed in position and the V edges
i.e., 1.87 miles anticipated length to be installed soldered, had the same diameter as the cable
plus 0.25 mile spare. itself.
The cable cores were made up in the same For mounting the large drum containing the
manner as for the land cable except that the completed lengths of single lead-sheathed cable
conductors were specially insulated to meet and for passing the latter through compound
subfluvial requirements. A double lead- tanks to the lead press for the second sheathing,
antimony alloy sheath, with a layer of compound special plant was installed. From the lead
separating the two sheaths, and single wire press the double sheathed cable was taken
armouring, were specified. once round a take-up drum, over a coiling sheave
In order to meet transmission requirements, and down to the floor of the shop. Here it was
each cable was manufactured in 12 lengths coiled, each layer being covered with sheets of
of 320 yards each. The necessary tests were plywood cut to shape.
carried out on each length in the core stage, In the final stage, the protective materials
after which a single lead sheath was applied. were applied. After passing through a com-
The two drums, each containing a single pound bath, the cable was lapped with two
length, were mounted adjacent to one another layers of paper, again compounded and served
256
EDINBURGH-ABERDEEN CABLE
Over wires 2.23 in.
», outside jute 2.53 in.
Cable Installation
Consideration of all the problems involved
indicated that it was desirable to lay the cables
direct from the vessel used for transporting them
to site. A motor vessel, the Glamis, having a
draught of only 64 feet, was, therefore, chartered
for the work and was brought alongside the
factory at North Woolwich to receive the
cable. Completed lengths of 3 837 and 3 843
yards, respectively, were coiled in separate
holds of the vessel on which suitable paying-off
gear was installed at the same time.
It was decided to commence the laying of
each cable at the north (Dundee) side.
The cable routes to be followed were first
plotted and buoyed with the aid of a motor
launch, four buoys. being placed to mark the
East or Go cable and five to mark the West or
Return cable. At a time dictated by the tide,
the West cable was first laid. The cable end was
prepared and a grip attached; it was then
passed up and around the overhead 4 ft. 6 in.
Fig. 1—River Tay Crossing—Paying out Cable via Large diameter cable sheave and through a special
Sheave and Special Jockey Sheave.
fitting of jockey sheaves and cable stopper
(Fig. 1). A line having been run to shore by
with jute yarn, armoured with 24-0.232 in. the motor launch, the pulling-in rope was
diameter galvanized iron wires, coated with two drawn on board and attached to the cable grip,
layers of compound and two servings of com- the end of the cable being pulled ashore by
pounded yarn, and white-washed overall. the land cable gang. Whilst this operation
The diameter of the cable at various stages was in progress it was necessary to employ a
of manufacture was: launch to hold the Glamis in position against the
Over Ist lead sheath 1.165 in. strong tide, a precautionary measure that was
» 2nd ,, ” 1.425 in. also necessary during the actual laying of the
»» papers 1.46 in. cable. The vessel then moved across the river
» jute 1.87 in. at an average speed of 3.25 miles per hour, the
2369 YDS.
592 YDS 625 YDS. S33 YDS. Gi3 YOS.
SOUTH NORTH
APPROACH APPROACH
E = ce
PO, HUTS TL SLACK BOX |
Sm DENOTES PATH OF CABLE
Fig. 2—Diagrammatic View of Forth Bridge and Cable Installation.
258 ELECTRICAL COMMUNICATION
Fig. 3—Forth
Bridge — End
of horizontal
aerial run on
G.I. strand on
south viaduct
and commence-
ment of rise on
south pier,
Fig. 4— Forth Bridge— Laying
cables from trucks (view taken from
top of south pier),
EDINBURGH-ABERDEEN CABLE
cable being paid-out mean-
while. ‘The Glamis hove
to approximately 75 yards
from the south shore and,
after measuring the length
of cable required, the sur-
plus portion was cut off.
After sealing both the cut
ends, the cable was landed
in a manner similar to that
adopted for the north side.
The next day a similar
procedure was adopted for
laying the East cable.
The actual lengths of
subfluvial cable installed
were 3390 and 3109 yards,
respectively, the surplus
length being handed over
to the Post Office for main-
tenance purposes. It had
previously been established
that variation in length
would not materially affect
transmission values. At
each side of the river the
cables were drawn through
ducts leading to existing
manholes, the cables being
anchored by iron brackets
and cement work to the rock
beds of the river walls.
THE FIRTH OF FORTH
CROSSING
Owing to the rocky
nature of the bed of the
Forth, the use of subfluvial Fig. 5—Forth Bridge—Vertical Suspension on North Pier.
cable was not possible,
and it was necessary, there-
fore, to lay the cables across the renowned Forth Apart from inherent difficulties in placing
Bridge carrying the railway line to the north. cables with various types of support on such a
The Forth Bridge, which was completed in structure, the problems of vibration and expan-
1890, is approximately 14 miles in length and sion and contraction needed careful considera-
consists of two main spans of 1 710 feet and two tion.
smaller spans with an approach viaduct at each On the east side of the bridge, five cables had
end. The height from high water mark to the been installed some years ago but trouble had
top of the cantilevers is 360 feet and to the developed due to the effect of vibration, etc.,
railway track 130 feet. Owing to the gales and it was decided to replace them with three
frequently encountered in this district, the new cables (one 160 pair 40 lb., one 54 pair
bridge was constructed to withstand a wind 70 Ib., and one 30 pair 70 Ib., all multiple twin
pressure exceeding 60 Ibs. per sq. ft. type) to be installed on the west side in con-
260 ELECTRICAL COMMUNICATION
fixed to the wall and are
PLUGGED WITH TINMANS protected by a suitable
OZOKERITE TAPE SOLDER
casing. Then for 570
yards the cables are sus-
pended, by means of
‘Elder’ type rawhide
RUBBER BANDAGE
suspenders with wire
PAPER WRAPPING
UNDERNEATH
RUBBER
CABLE METALLIC TUBE clips, from G.J. strands
erected on __ brackets
Fig. 6—Plug Joint used for Connecting Lead-covered Cable to Rubber-sheathed
Cable enclosed in Flexible Metallic Tubing. bolted to the under-
structure of the viaduct
at 20-foot intervals.
junction with the two 12-quad carrier cables A boarded footway with handrail existed on this
forming part of the main Edinburgh—Aberdeen understructure but it was necessary to remove
project. All five of the new cables were sheathed the handrail to enable the cables to be lifted intc
with lead-antimony alloy. Sections to be position. Since this portion of the bridge was
installed on the cantilever portion of the bridge 130 feet above water-level and the work was
were in addition to be served with compounded carried out under gale conditions, great care was
hessian to lessen the effect of vibration. required to avoid accidents.
For the purpose of this description, the bridge It was next necessary to negotiate the rise
may be considered to be divided into three and fall from this understructure to the
portions: the south viaduct of 592 yards; the cantilever portion at the south pier (Fig. 3).
main cantilever portion of 1777 yards between Here the cables were protected with flexible
the south and north piers; and the north metallic tubing and were securely clamped tc
viaduct of 350 yards (Fig. 2). racks with cork bedding for damping vibra-
tion. Arriving at the permanent way the cables
Cable Installation for some 1 780 yards were laid in a galvanizec
The cable route commences in cable huts iron trough 68 in. wide by 93 in. deep, fitted witk
near the foot of the south approach to the south covers having two side lips secured by iror
viaduct. Leaving the ducts near the cable huts, straps bolted round the whole. This troughing
the route proceeds up the wall of the south had already been provided ; before the cables
viaduct and along the understructure girder- were placed in position, three layers of }in.
work, passes out to the wall of the south pier, felt were laid in the bottom of the trough to aic
rises vertically for 35 feet, passes round the in the all-important object of damping out
inside of the pier archway, and then down vibration.
14 feet to the level of the permanent way. From Cabling operations on this portion of the
this point the cables are installed in an iron route had to be carried out in conjunction witk
trough at the side of the railway track for a the railway authorities, Sunday afternoon being
distance of 1 777 yards to the north pier, where the only time when single track working coulc
they pass through and drop down and round the be arranged in order to permit of using the othe1
outside of the side girders to a platform track for the cable trucks (Fig. 4). As ar
immediately beneath the permanent way. From indication of the difficulties encountered, it
this platform they are vertically suspended for might be mentioned that part of this cabling
120 feet and pass into a manhole at the foot of work was done in an 80-mile gale, and the
the north pier, whence a short distance in ducts emptied drums had to be nailed to the trucks
completes the route. The total cable route to prevent their being blown on to the line.
length is approximately 1.46 miles. The felt-bedded trough, in which the cables
Dealing with the sections of the route in were placed, was finally filled with a specia’
more detail: The cables rise approximately compound as a protection against cable damage
30 feet from the ducts at the south approach; by rubbing caused by the almost constan:
they are clamped every two feet to G.I. strands vibration set up by passing trains. This
EDINBURGH-ABERDEEN CABLE 261
compound, which consisted largely of French weather. It proved somewhat difficult to
chalk, was not sufficiently liquid for pouring or arrange adequate support at the top of this
bailing, but the application of heat rendered it suspension as the total weight of cable, suspen-
sufficiently plastic to be scooped out of the sion strands, and fittings was about 34 tons. The
container. Some 35 tons of the compound, under-girders of the bridge to which the weight
supplied in 1 cwt. tins, were used. This, together could be attached safely were at that particular
with about 14 tons of firing, was taken out on a point subject to a 5-inch movement due to
ballast train on a Sunday afternoon and dis- expansion and contraction, which would have
tributed as conveniently as possible on the six- resulted in the cables fouling the iron edge of
foot way along the length of the trough. The the permanently slung footway with consequent
railway authorities limited the number of sheath damage. It was finally decided to
braziers in use at any one time to six. A suitable combine two alternatives, using the wall fixing
type. with special heating containers was partly to take the weight and definitely to posi-
designed ; it could be placed on boiler plates tion and terminate the strands, while a secondary
in the six-foot way with no danger of being and moveable suspension of steel eyebolts was
fouled by passing trains, or of the container brought out from the wall fixing to the main
falling from the brazier during heavy vibration. girders a few feet above. The cables were
While the compound was
being heated, constant
stirring was necessary to
prevent caking or burning.
When sufficiently hot it
was carried to the trough
and, with the aid of scoops,
a layer of compound was
placed on top of the felt
bedding, the cables being
lifted and then pressed
down into the compound.
As compound was added,
it was tamped down so that
each cable individually was
surrounded by compound.
From the end of the
trough the cables were laid
under the bridge structure
on hangers and then
dropped vertically down
the granite buttress of the
north pier, 120 feet to the
ground level (Fig. 5). Five
suspension strands were
secured at the top by iron
wall and girder fixings, and
at the bottom by anchor
irons. They were further
secured by iron brackets
at 15-foot intervals for the
whole length of the sus-
pension to prevent
Fig. 7—Forth Bridge—foints and Slack Box at South Pier.
swinging during windy
262 ELECTRICAL COMMUNICATION
clamped to the strands at 2-foot intervals and, the opposite joint box is so designed that,
at the foot of the run, suitable protection against during contraction and expansion of the bridge,
mechanical damage was provided. it slides backwards and forwards in the slack
In all, 68 lengths of cable were placed, box without actually emerging. The lead-
totalling some 7+ miles; 46 cable joints were covered cables terminate in the joint box and are
made in addition to the 40 “‘plug’’ joints referred connected by means of plug joints to rubber-
to hereinafter. sheathed cables encased in flexible metallic
In the cantilever portion of the bridge, the tubing, sufficient slack being left to prevent any
cable is laid in troughing divided into three tension being placed on the cables during the
main lengths with cable slack boxes to take period of maximum contraction of the bridge
flexible connections at each end and at two (Figs. 6 and 7). All these special flexible tube
intermediate points, the four positions coincid- plug connections, twenty in number and ranging
ing with the “broken” points of the bridge. from 14 to 28 feet in length, were made up, air
The movement (expansion and contraction) at pressure tested, fitted with rubber cable sheathed
each intermediate position is about ten inches cores, and transported to the various positions
and is allowed for in the construction of the they were to occupy on the bridge by means of
bridge, the end of one cantilever section sliding ladders lashed to barrows.
in and out of the adjacent section without Electrical testing work was carried out in the
actually forming a gap when fully contracted. normal manner, and sustained air pressure tests
At the north and south piers, the movement is were made on sections of cable between slack
only five inches and takes place on large steel boxes.
rollers fitted into recesses in the piers.
The working principle of the slack boxes is CONCLUSION
as follows : Grateful acknowledgment is due to British
At one end of a section of the main trough Post Office engineers and to The London and
and at the beginning of the next section are North Eastern Railway officials for their co-
enlarged portions described as joint boxes. operation in facilitating the successful conclusion
Between the two adjacent ends of the joint of the Edinburgh—Aberdeen cable installation,
boxes is a still larger portion, six feet in Jength, part of which was accomplished under hazardous
known as a slack box. The end of one joint box conditions, without mishap to any of the
is a fixture to one end of the slack box, whilst personnel.
New 3-Channel Open-Wire Carrier Telephone System and
its Application in Norway
By S. RYNNING TONNESEN, N.T.H., M.N.IF., M.N.E.F.,
Eng. Sup. Telegrafstyret, Oslo, Norway
an
A. M. THORNTON, B.Sc., A.R.C.Sc.,
Standard Telephones and Cables, Limited, London, England
INTRODUCTION however, and the ever-increasing demand for
HREE-CHANNEL Carrier Telephone more exacting performance led to the redesign
systems designed to provide three of the equipment. This article describes the
additional speech circuits on an open- new 3-Channel Carrier Telephone equipments,
wire pair have been in operation for several the first three of which have recently been
years and, owing to their widespread application installed in Norway.
and the amount of literature available on the
FREQUENCY ALLOCATION
subject, their fundamental principles of opera-
tion are well known. Two systems, known as the SOS.3 and
The earliest SOT.3, are
systems of available,
this type to —_ cS Che oe Gre cHT cha] T.0.4-HF TELEGRAPH differing only
we . 7 o7 14-0] 164 19-6: 234 SYSTEM . .
be utilized in a a Na» defo w in their fre-
1 a r & € num- “ewe bee ‘el —— a eet —_! CS 4 8900 3740 quency allo-
bers were * *¢ 139 104 a 7 apr cation (Fig.
known as the .ee
al we ee
CT
1.
Cc N. 3 an d a + meen we! a a SOS. 3 The 508.3
CS.3 Carrier
7
a
5
by 5 Sao : 10-8
ee
7.
Teme sors
2T7
type uses the
Telephone aul ap xe BA same fre-
systems and at} ttt to.4 34.0 42:5
quencies as
10-3
were describ-
62
belt 50-1, wot ! the former
.
edinan article jee] CS. systems,
in this jour- ( 5 lo 15 20 25 30 35 40 45 while the
nal in 1929.1 FREQUENCY = ROS SOT.3system
These two Fig. |\—Frequency Allocation of Open-Wire Carrier Systems. uses a new
systems of frequency
the single sideband, suppressed carrier type allocation in the low group, or A-B direction
were essentially similar but their carrier fre- of transmission, and the same as the CT. type
quencies and the consequent location of the system in the high group or B-A direction.
transmitted sidebands in the frequency range The SOT.3 frequency allocation allows a
were “staggered” so that a system of each type newly developed 4-channel high frequency
could be operated on the two side circuits of a carrier telegraph system, occupying the range
phantom group or on two pairs on the same 4 ke to 7kc, to operate on the same open-wire
pole route with comparatively simple trans- pair.
positions and without intelligible crosstalk.
CIRCUIT ARRANGEMENTS
Although minor alterations have been made,
including the addition of a CT. type with The circuit arrangements of the systems
different frequency allocation, these systems supplied to Norway are illustrated in schematic
have remained substantially the same for the last form, Fig. 2 showing the terminal and Fig. 3
ten years. Recent improvements in technique, the repeater connections.
Referring to Fig. 2, the voice frequency
4“ Carrier Current Systems and Their World-Wide speech currents enter the circuits via a pad and
Application,” by J. S. Jammer, Electrical Communication,
April, 1929, then pass through the ringer and 4-wire
263
264 ELECTRICAL COMMUNICATION
vou
LIMITER
WIRE REPEATER
SEND
PAD RINGER
c
RecA INE: ru.
4WIRE REPEATER
REC,
DEMOD
‘AMP. mma
———
eaunns FED, ‘CON PANEL,
oom Reerir
cH
cH PILOT PILOT
IND. ALARM
Fig. 2—SO.3 System. Terminal Schematic.
terminating set. The pad circuit is utilized in components from the modulator is much lower
a special way in Norway, details of the arrange- than on the older type of equipment. The
ment being given later. The transmitting path output from the modulator is taken to the
goes via one-half of a 4-wire repeater to the modulator band filter which selects the required
modulator, across the input of which is bridged sideband. ‘The band filters employ ‘resonant
a neon tube voltage limiter. This prevents the units’ each comprising an inductance coil, a
passage of excessive peak voltages which might fixed condenser and a small variable trimming
overload subsequent portions of the circuit. condenser, and each unit is carefully adjusted
The presence of this limiter is not noticeable to resonance or anti-resonance before the filter
to the user of the circuit. is assembled. Very accurate filters can be made
The modulator employs metal type rectifiers in this way and, by means of equalization
and is similar to that illustrated and described incorporated in the modulators and demodula-
in a previous article in this journal,” so that a tors, good quality can be obtained within quite
detailed description is not now necessary except close limits.
to state that the relative level of unwanted From the three modulator band filters,
which are connected in parallel with each other
*“ Bristol—Plymouth 12-Channel Carrier System,’ by and a compensating network, the outputs pass
Col. A. S. Angwin and R. A. Mack, Electrical Communica-
tion, October, 1937. through a pad to the transmitting amplifier and
PILOT
INO.
A-BIN coil FIXED VARIABLE EQUAL"S A-BOUT
FILTER PANEL, EQUAL® FILTER
CI
HPLINE He LINE
FILTER FILTER
Toa
TER HINAL TOR
TERMINAL,
LPLINE B-AOUT “A coll, B-AIN LPLINE
FILTER FILTER AMP. VARIABLE EQUAL"® EQUAL" PANEL, FILTER FILTER
PILOT
ND.
Fig. 3—SO.3 System Repeater Schematic.
3-CHANNEL CARRIER SYSTEM 265
thence through a transmitting directional filter 2 nepers) above reference telephonic power.
and so to line through the high-pass line filter. The input and output impedances are 600 ohms.
The transmitting amplifier, which is also Variations in gain are obtained by 5 and 10 db.
identical with the receiving amplifier, is of the pads connected in circuit by U-links in con-
feedback type and is similar in principle to that junction with a potentiometer which is con-
described in the article on the Bristol-Plymouth tinuously variable over a range of 14 db.
12-channel system already referred to. The It may be noted that when the SOT.3 system
maximum gain is 50 db. and the output power is required to operate on the same pair as a
capable of being handled is approximately 4-channel H.F. telegraph system, high and low
23 db. above 5.9 mW although the normal pass telegraph separating filters are necessary
operating level is + 18 db. (approximately between the high pass line filter and the
Fig. 4—SOT.3 Terminal (8’ 6” bays)—Front View with Covers Removed.
266 ELECTRICAL COMMUNICATION
telephone system directional filters. The station, and, in addition, for the deviation in
Norwegian systems, however, are not operating loss with frequency of 100 miles of 4 mm
on this basis. copper, open-wire line. ‘Two more variable
The receiving portion of the circuit com- equalizer panels are located between the basic
mences at the receiving directional filter, equalizer and the receiving amplifier; and, by
followed by the basic equalizer which is designed means of simple U-link connections, these can
to compensate for losses near the cut-off be arranged to give changes in equalization of
frequencies of the receiving directional filter approximately 1 db. per ke in steps of 0.1 db.
and the corresponding transmitting directional per kc over the frequency range occupied by the
filter at the other terminal or nearest repeater group of three channels. Unless there is some
Fig. 5—SOT.3 Terminal. Rear View with Covers Removed.
3-CHANNEL CARRIER SYSTEM 267
4-A—Equipment BUSBARS BUSBARS BUSBARS BUSBARS BUSBARS
Fig,
Layou t— Front FUSES FUSES FUSES LAMPS AND FUSES FUSES
,
correspon ding to RES. LAMPS RES.LAMPS LAMPS AND FUSES LAMPS ANO FUSES
Fig.& 4. ALARM LAMPS | ALARMLAMPS ALARM LAMPS | ALARM LAMPS RES. LAMPS
AND RELAYS AND RELAYS AND RELAYS AND RELAYS
NO VOLT ALARM | CHANNEL PANEL | CHANNEL PANEL ALARM LAMPS
TEST cH.I CHE AND RELAYS
OSCILLATOR | MOD. OSCILLATOR | MOD. OSCILLATOR PILOToer
ost SPACE FOR
ALARM LAMPS
DEMOD. OSCILLATOR |DEMOD. OSCILLATOR AND RELAYS
TRANSMIS SION 1 2 INTERRUPTER
MEASURING VOLTAGE CIMIFER | VOLTAGE LIMITER PILOT RELAYS
Q D
RECEIVE DEMOD. AMP. DEMOD. AMP. INDICATOR osene ctor
TRANSMISSION a WIRE
REPEATER 4 WIRE
REPEATER SPARE
MEASURING SET 1 @ 500~ OSCILLATOR
u- LINKS U-LINKS U>LINKS U-LINKS UI LINKS ee
METERS
METERS
METERS
REPO- TER PILOT RINGER TEST
METERS 3 ALARM PANEL PANEL
TELEPHONE RECEIVING VOLTAGE LIMITER
PANEL AMPLIFIER AND DEMOD.
3 AMP. [ SPARE
RINGER
TELEGRAPH SET DEMOD. OSCILLATOR
COMP. NETWORKS | 3 RINGER |
MOD, OSCILLATOR
3
Re eR” | CHANNEL PANEL RINGER @
3
[RINGER 3
GRID BATTERY SPACE
PANELS ONCERFOR
TEST BAY AMPLIFIER BAY. CHANNEL BAY PILOT BAY RINGER BAY
BUSBARS BUSBARS USBARS BUSBARS BUSBARS
TERMINAL STRIPS
TERMINAL STRIPSITERMINAL STRIPS |TERMINAL STRIPS| TERMINAL STRIPS [BATTERY SUPPLIES
BATTERY SUPPLIESIBATTERY SUPPLIES|BATTERY SUPPLIES
SPACE FOR
RINGER
”
IN
TERMINATING SET|TERMINATING SET] LOW
|ecu PASS
-teR
meugeeve | cERENS
: : Thien, pags
LINE FILTER
”
MOD. BAND MOD. BAND ”
FILTER.| FILTER 2
"4
U- LINKS U-LINKS U -LINKS
VARIABLE LINE MOD. BAND |SPARE LOW PASS -
EQUALISER FILTER. 5 LINE FILTER
VARIABLE LINE DEMOD. BAND [SPARE HIGH PASS
EQUALISER FILTER. 3 LINE FILTER
BASIC
EQUALISER ”
RECEIVING 3
DIRECTIONAL
FILTER
Fig. 5-A— Equipment
37 . -
TRANSMITTING Layout — Rear,
DIRECTIONAL SPACE FOR
FILTER pace corresponding to
Fig. 5.
TEST BAY AMPLIFIER BAY CHANNEL BAY PILOT BAY RINGER BAY
268 ELECTRICAL COMMUNICATION
half of the 4-wire repeater, and then pass
through the terminating set of the 2-wire line
and ringer.
The sending portion of the ringing panel is
quite simple, consisting principally of a relay
operating on the 20 p:s ringing current from
the switchboard which sends 500 p:s current
interrupted at 20 p:s to the carrier equipment.
The receiving portion incorporates several new
features which render it more stable than the
Nee old type and less liable to false operation on
speech. A high impedance circuit is bridged
across the 2-wire line and a small portion of the
incoming current is amplified and passed to
three tuned circuits which contain metal type
rectifier elements. These three circuits are
tuned to 500 p:s, 600 p:s and 750 p:s,
respectively, and relays connected in the D.C.
side of the rectifier bridges are operated accord-
Fig. 6—SOS.3 and SOT.3 Terminals at Notodden
(8’ 6” bays).
very serious irregularity in the line, therefore,
very good overall quality can be obtained
because all normal deviations in the loss/fre-
quency characteristic can be compensated.
Abnormal deviations can be equalized by
means of special channel equalizers which are
inserted at the input to the modulator and
output of the demodulator. Provision is made
for these panels on the bay, but in Norway they
have been found to be unnecessary and there-
fore have not been connected in circuit.
After passing through the basic and variable
line equalizers, the carrier currents are amplified
in the receiving amplifier and then go through
a 6 db. pad to the three demodulator band
filters and associated compensating network.
The output from each band filter is applied
to the demodulator, which is similar to the
modulator in design but which also incorporates
a low-pass filter to eliminate unwanted fre-
quencies above the voice range. The voice
frequency currents are amplified by the demodu-
lator amplifier and, if necessary, by the receiving Fig. 7—SOS.3 Terminal at Kristiansand (10’ 6” bays).
3-CHANNEL CARRIER SYSTEM 269
ing to the composition of the incoming waves.
Thus, 500 p:s current, either interrupted or
continuous, causes the corresponding relay to
operate; and, providing no 600 or 750 p:s
currents are present, the ringer operates and
transmits 20 p:s to the switchboard. If the
500 p:s current is spasmodic or if 600 or 750 p:s
frequencies are present, which would be the
case with speech, the delay on the 500 p:s
relay is sufficient to render the ringer inoperative
and, as an additional safeguard, the quick-
acting relays in the 600 and 750 p:s circuits
would operate and effectively form a “guard”
to prevent operation of the ringer.
REPEATER CIRCUITS
Fig. 3 shows a schematic of a repeater, one
of which is located at Kristiansand on the
Notodden-Stavanger SOT.3 system. This
follows well-established principles of carrier
telephone repeater design and the components
are identical with those described above in the
receiving portion of the terminal. Incoming
high frequency currents pass through the high-
pass filter of the line filter set to the directional
filters which separate the high and low trans-
mission groups. A transformer connects the
balanced directional filters and unbalanced basic
and variable equalizers, which in their turn
are connected to an amplifier. The output
from the amplifier goes to the output directional
filter and high-pass line filter to line. The Fig. 8—SOT.3 Repeater at Kristiansand.
reverse direction of transmission is similar.
PILOT CHANNEL example, in the A-B direction on the SOT.3
Pilot channel equipment is used to indicate system, a frequency of about 14.25 or 10.85 ke
the change in line attenuation due to weather would be used, preferably the former. The
changes or other circumstances. On_ the pilot frequency is actually located at about
systems described herein a manual pilot is used, 50 p:s outside the carrier frequency in order
i.e., the changes in gain settings of receiving to avoid interference with the channels in the
amplifiers and repeaters are controlled by the same direction of transmission. As this is near
maintenance staff manually instead of by the cut-off of the adjacent band filters the
attenuation inserted or removed automatically impedance facing the output of the pilot
from the input circuit of these amplifiers by oscillator is liable to large changes with a small
means of rotary switches, which in turn are change in pilot frequency and this would con-
controlled by the level of the pilot current itself. sequently affect the output power. The pad
The pilot current is a single frequency between the band filters and terminating
current introduced at the input to the trans- amplifier is therefore inserted to mask this
mitting amplifier. The frequency is chosen to impedance change and minimize the effect of
be approximately in the middle of the range of the filter impedance. The pad at the output of
the directional group, the higher of the two the receiving amplifier and input of the pilot
available frequencies generally being used. For indicator panel serves a similar purpose.
270 ELECTRICAL COMMUNICATION
the pilot level changes by
more than a_ pre-determined
level, usually + 14 db. After
Héi
a suitable delay to allow for
momentary surges, the alarm is
given and the maintenance
NORWAY personnel alter the gain setting
\ of the receiving amplifier until
OSLO c
the pilot indicator reading is
e ore & restored to normal. In general,
NOTOOOEN
the gain of the amplifier at a
.o,A repeater station is not changed
mos© \ SKIEN except under instruction from
SY)
STAVANGER, the control terminal, although
H59)
experience may prove other
SWEDEN methods of procedure to be
773 ARENDAL more suitable in particular
sory cases.
Owing to the severe climatic
58 KRISTIANSAND.
conditions experienced in
° Norway and the consequent
variations due to sleet and ice,
ENGLISH MILES a pilot channel is essential even
© 10 20 30 40 so 60
pes Fr on short, one-section systems
© 10 20 30.40 50 60 7 8090 és
s7H KILOMETRES 19) such as Notodden—Arendal.
LS
e 7 8° 9° i0°
EQUIPMENT
Fig. 9—Map showing Routes of New Systems. The equipment is mounted
on both sides of rack frame-
The pilot current is transmitted at a level of works 8’ 6” or 10’ 6” high, according to the
approximately 1 mW at the output of the height of the apparatus room. Bays 10’ 6”
transmitting amplifier or about 25 db. below high have been provided at Kristiansand and
the maximum speech power on any one channel Stavanger and 8’ 6” high at Notodden and
at this point. Arendal. Aluminium finish is used throughout
At the repeater the pilot level is continuously on racks and components.
indicated by a suitable meter, which is con- Fig. 4 shows a front view of an 8’ 6” terminal
nected in the output circuit of the pilot indicator
panel. This panel consists of a sharply tuned
input circuit of high impedance followed by an
amplifier, and, although similar in function to
the older type of indicator panel, is much
improved in stability by the incorporation of
LINE a! LM
feedback in the circuit. Only a very small
portion of the pilot current is absorbed by this RINGING RELAY
panel, almost all of it passing on to succeeding
repeaters and the terminal where similar
indicators are located.
At the terminal, an alarm panel is also con-
nected in the pilot indicator circuit. The chief
feature of this panel is a sensitive polarized
relay which closes one or other of its contacts if Fig. 10—Terminations for Physical Lines.
3-CHANNEL CARRIER SYSTEM 271
with the panel covers
removed. A key to the
\ 7
apparatus panels is
given in Fig. -4-A.
Figs. 5 and 5-A show
a!
the .arrangement of
apparatus on the bays
viewed from the rear.
pl.
It can be seen that
the general principles )
adopted are as follows :
Battery bus-bars are Fig. 11—Cord-circuit Repeater.
located at the top of all
bays followed by fuse
and lamp panels; below them is placed the and spare 500 p:s oscillators and ringer test
miscellaneous apparatus associated with plate panel, and has space for 13 ringers, i.e., sufficient
circuit alarms, fuse alarms, etc. to equip four 3-channel terminals and one
The main apparatus panels are arranged so spare ringer panel. A second ringer test panel
that apparatus which requires to be handled is is provided on the rear of this bay when the
as far as possible within easy reach of the rear is equipped with ringers.
maintenance staff. On the particular terminal The main feature of the test bay is the
shown, the channel apparatus, line amplifiers, Transmission Measuring Set which measures
equalizers and directional filters occupy two losses and levels from -—30 db. to + 30 db.
bays, while the pilot channel equipment and over the whole voice and carrier frequency
normal and spare line filter sets are mounted on range utilized by the system. An 800 p:s
another bay. The ringer bay mounts the normal oscillator is provided for testing purposes. ‘The
DEMOD. DEMOD,
6002
4-WIRE
TERMINATING|
SET
RINGER
RINGER
6000S
INEPER.
7
LM 77
~~ r
LM
$
E
=e
RINGING RELAY RINGING RELAY
—__t
6000s] oy IM fMr——t
SS eT L__fliag
UP STATION DOWN STATION
Fig. 12—Terminations of 3-channel Carrier Telephone Circuits.
272 ELECTRICAL COMMUNICATION
station, together with
OSLO KONGSBERG NOTODDEN ARENDAL the line filters for the
re 86 km P<] 33 Kg
Notodden - Stavanger
1-4 mm
1Ooftod mH
4mm
177/63 mH repeater.
CABLE
CABLE
There are very few
connections between the
t2N ZaKe various bays. Little
difficulty would there-
° 7
+0'Saib
+0-1.N fore be encountered in
FM .
qe" PAD (85 ab) removing the system
LM to another position
within the station or
—
IS KC +17alt to another location
should occasion arise.
xLM REPEATER
f I+. N. PAD (8-Sdib) EQ UIPMENT
ne Ln PON FM
“FON he
-O' BN
4b,
—-8:5db. 7 este The repeater equip-
Fig. 13—Typical Channel Line-up, Oslo—Arendal. ment at Kristiansand is
shown in Fig. 8. This
has been provided with
system can be adequately maintained by these its own test bay which is capable of serving
means; facilities are provided, however, to four repeaters. Normally, a high frequency
enable the T.M.S. to be used with a high oscillator with the seven frequencies of 4.5,
frequency oscillator, if necessary. 6.5, 8, 15, 20, 28 and 40 ke is equipped on this
One test bay will serve two terminals if the bay, but, since a high frequency oscillator
line-up of the bays is convenient. An example already existed at the station, it has been
appears in Fig. 6, which shows two ter- omitted at Kristiansand. The amplifiers,
minals at Notodden with the test bay in the equalizers and directional filters are mounted on
centre. the next bay followed by the pilot apparatus bay
The layout of the apparatus on 10’ 6” bays and the carrier line filter bay.
differs slightly from that already described and
is illustrated in Fig. 7, which shows the SOS.3A BATTERY SUPPLIES
terminal at Kristiansand. ‘The left-hand bay The normal 24 V and 130 V station battery
is the ringer bay and is similar to the 8’ 6” bay supplies are used, the current drains being as
except that 19 ringers can be equipped, i.e., follows :
sufficient for six terminals and one spare. The 24V 130V
channel bay mounts the channel apparatus for Amps. Amps.
One Terminal including 4-wire
all three channels but the arrangement differs repeaters, ringer and manual pilot
from that adopted for the shorter bay. Thus, equipment . we . 8.5 0.42
Testing equipment when required 1.25 0.03
the three 4-wire repeaters are mounted above One Repeater including manual pilot 5.2 0.18
the U-link panel, while below are the three Testing equipment when required ~ 1.25 0.03
demodulator amplifiers and then the modulator
and demodulator oscillators. Static equipment APPLICATION OF SYSTEMS IN NORWAY
which does not require adjustment, such as the The routes on which the first three systems
channel panels and band filters, is on the rear of this type have been installed in Norway are
of this bay. The pilot equipment is mounted on shown in Fig. 9.
the same bay as the line amplifiers, equalizers One SOT.3 system operates on one side of a
and directional filters. The test bay is similar phantom group between Notodden and Arendal,
to that already described. The line filters are a single channel DA. system being on the other
mounted on a separate line filter bay in this side-circuit between Notodden and_ Skien.
3-CHANNEL CA RRIER SYSTEM 273
A second SOT.3 system operates between repeaters are used, connected as shown in
Notodden and Stavanger with a repeater at Fig. 11. Each physical circuit is provided with
Kristiansand. Between Notodden and Kristian- a simulating network for use with cord-circuit
sand, this system works on the same phantom repeaters and carrier channels. ‘To simplify
group as the Notodden—Kristiansand SOS.3 switching, the 4 leads normally associated with
system. A carrier broadcast channel is also line and network are reduced to 3 leads, one of
operating on one of these circuits in the which is common, so that three conductor plugs
frequency range above the telephone system. and cords can be used. The method of con-
The distances between the stations are approxi- necting this network and the associated LM
mately as follows : (long line multiple) and FM (repeater multiple)
Miles . Kilometres switchboard jacks are shown in Fig. 10.
Notodden—Arendal . . 112 180
Notodden—Kristiansand 175 280 Physical lines of the order of 1 neper (or
Kristiansand—Stavanger 156 250 8.5 db.) equivalent are not repeatered; if the
The line consists of 3.3 mm copper on the loss is much greater, however, they are repeatered
Arendal route and 4.0 mm copper on the and lined up to 1 neper (or 8.5 db.).
Kristiansandroute; intermediate lengths of cable The terminations of carrier channels are
are loaded for operation at carrier frequencies. shown in Fig. 12. These channels are lined
All the terminals at Notodden are ‘“B” up to zero equivalent from FM jack to FM jack
terminals, i.e., they transmit the high group of but operate on an “up” and ‘‘down”’ station
frequencies and receive the low. Between basis, the “‘down” station having a pad of
Notodden and Oslo, the derived voice frequency 1 neper (or 8.5 db.) inserted between the
channels go forward in 2-wire cable circuits LM jack and terminating set. Thus, levels
with repeaters at Kongsberg. ‘The ringers for throughout the systems in the direction “up”
these nine channels are located in Oslo. to “down’’ are normal on a zero equivalent
The carrier circuits in Norway are not lined basis, but levels in the direction ‘“‘down”’ to
up in the manner usually employed for pad “up” are arranged to give correct transmitting
switching or “tail-eating” terminations. Figs. and carrier repeater outputs when the input to
10, 11 and 12 illustrate the method of switching the terminating set is — 1 neper (or — 8.5 db.).
interurban lines pending completion of the This means that the transmitting gain is
4-wire circuits which
are in course of con-
struction.
HA
SWITCHING NSAND
o
L
PRINCIPLES
db.
HAN.
The broad principles
Sh,
ATTENUATION
on which the present
switching arrangements
for the routes in ques-
°
2000
ny
+
tion are based are as
follows :
No 4-wire circuits or
repeaters are used and rir
KRISTIANSAND,
the number of 2-wire
ta.
ft alee
db
HA
repeaters is kept at a
N
ATTENUTION
minimum. These re-
"f
peaters are located inthe
~
tat
middle of circuits and
J
1_|
2000
&
not at the ends. Where | TTT TTT
TEP TT rr err
terminal repeaters are Fig, 14-——Overall Quality—Notodden—Kristiansand.
necessary, cord circuit
274 ELECTRICAL COMMUNICATION
repeater is not available a direct connection can
be made, the balance at the “down” end, which
is normally quite good (due to the pad or the
correct network), maintaining the singing margin
of the channel. The levels throughout the
7
3 aneee carrier system, however, will be approximately
; EEE 8.5 db. lower than normal. To couple a physical
E ttt circuit to a “down” carrier channel a direct
connection is made from the physical FM jack
to the carrier FM jack. The balance on the
hybrid coil is perfect and the levels throughout
40 ry 20 Ey x» the systems are correct.
FREQUENCY KC/S
Fig. 15—-Open-wire Line Attenuation—Notodden—
Kristiansand. LINE-UP OF CIRCUITS
Fig. 13 shows the levels on a typical carrier
channel on the Oslo—Arendal system after
normally 2 nepers (17 db.) in-the “‘up”’ station applying the above principles. The level of
and 3 nepers (25.5 db.) at the “down” station. —0.45N (— 4 db.) at the 4-wire terminating
All carrier circuits terminating in Oslo are set at Notodden was chosen partly because it
operated as for an “up” station, but places such enabled the Kongsberg repeaters to operate
as Trondheim and ultimately Kristiansand will with an output at zero level and partly because
have LM and FM jack circuits of both “up” a convenient testing power of 1 mW — 4 db.
and “‘down’’ type. is available from the transmission measuring
set. Special precautions had to be taken
OPERATION OF SWITCHING CIRCUITS
regarding the ringers and ringer test sets, as at
The operator always answers on the LM the ‘“‘down’’ stations these were effectively
jack, which is also used for terminating calls transmitting at a level of — 1 neper (—8.5 db.)
and local connections. A straight-through and receiving at zero, whereas at the “up”
physical to physical trunk connection, not stations the converse was the case. It was
requiring a cord-circuit repeater, is completed actually found in practice, however, that
by patching from LM to LM jacks. If the operation is satisfactory if the ringers are set to
connection involves coupling two physical lines operate at a level of — 0.45N (— 4 db.) for
through a cord-circuit repeater, the operator both transmitting and receiving. This avoids
connects the repeater (Fig. 11) across the two difficulty in spare ringer adjustments and ringer
sets of FM jacks (Fig. 10), thus terminating test panel settings at stations where both “up”
both sides of the repeater with the correct and “‘down’’ terminals are installed.
networks. The cord-circuit repeater is normally
set to give a gain of 1 neper (or 8.5 db.).
OVERALL QUALITY
For terminating calls on a carrier channel the
LM jacks are employed, but to connect an “up” Typical overall quality measured between
to a “down” carrier channel or vice versa, the _4-wire terminating sets on the carrier channels
connection is made with a straight three con- is shown in Fig. 14; the corresponding
ductor cord between the FM jacks, the overall measured line attenuation is shown in Fig. 15.
equivalent being thus maintained at 1 neper —
(or 8.5 db.). The general rule is to plug first NOISE MEASUREMENTS
into the “up”’ station jack in order to secure the The noise on the channels was measured
network for the “down” station without leaving with a 74100 type Psophometer and was found
the latter open. to consist chiefly of D.C. telegraph and radio
A physical line would normally be connected interference. The noise, however, was quite
to an “up” carrier channel via a cord-circuit small and only on channel 2 at Kristiansand was
repeater and the FM jacks. If a cord-circuit a value of 2.0 mV exceeded on occasions as a
3-CHANNEL CARRIER SYSTEM 275
result of severe radio interference, a disturbing giving excellent service. ‘The new features
E.M.F. of 3.0 mV being measured at times on incorporated in the equipment, notably the
this channel. This was due to temporary stabilized amplifier and pilot equipment, static
unbalance conditions existing on the open-wire modulators and variable line equalizers have
lines in question and would not be experienced proved very. satisfactory. In addition, the
with these lines in their normal condition. replacement of jacks by U-links in the trans-
Otherwise the noise at Arendal and Kristiansand mission circuits and the introduction of level
did not exceed 0.22 mV on any channel measured measurements have greatly facilitated testing
at receiving toll test board level. On the longer and maintenance compared. with the older type
repeatered circuit between Notodden and of systems.
Stavanger, noise measured at Stavanger was : It may be mentioned that two more systems
Channel 1 04 mV are being installed—one between Kristiansand
Channel 2 0.14 mV and Stavanger and the other on the Lillestrém—
Channel 3 0.14 mV
Trondheim route with a repeater at Lille-
As was to be expected from a system employ- hammer.
ing feedback amplifiers, no appreciable inter- Finally, the authors wish to express their
channel crosstalk could be detected. appreciation to Mr. A. Wager of the Norwegian
Telegraph Administration for his collaboration. °
CONCLUSION
The systems described above have been in 3 Forbedring av Langlinjetransmisjonen,’’ by Ved. avd.
ing Alf Wager, Tekniske Meddelelser fra Telegrafstyret,
operation for approximately one year and are October~Decermber, 1935.
oe
Paris Radio Show, “Grand Palais,’ September, 1938. Le Matériel Téléphonique Radio Receiving
Set Stand with Television Booth in centre. Additional displays included Television, Radio
Goniometry, High Power Radio Tubes, Piezoelectric Crystals, Cathode Ray Tubes, Hot Cathode
Mercury Vapour Rectifier, Selenium Rectifiers with Transformers, Rotary Automatic Telephone System
(working model), Teleprinters, Photoelectric Smoke Detector built to the order of Cte. Maritime
Sud-Atlantique for the S.S. “Pasteur,” as well as Photoelectric Automatic Counters, Luxmeters, Photo-
graphic Exposure Meters, etc.
A 1000 watt L.M.T. Public Address System supplied the main loudspeakers throughout the
Exhibition, Its output was also used to modulate a high frequency current which was fed to the
stands of all exhibitors for demonstrating their sets.
Theoretical Relationships of Dielectric Guides (Cylindrical)
and Coaxial Cables*
By A. G. CLAVIER,
Les Laboratoires, Le Matériel Téléphonique, Paris, France
ROVISION in a single cable of a large of a centimetre wave technique—a technique
number of communication channels, involving production, modulation, amplifica-
or a television bandwidth, at present tion, and demodulation, and imposing numerous
necessitates resort to a special type of cable new and difficult problems. Thus, the general
composed of two conductors cylindrically application of hyper - frequency waves in
coaxial, It is interesting to note that another dielectric cables can hardly be visualized for
solution, utilizing the propagation of electro- some years; nevertheless, exploration of the
magnetic waves through a dielectric guide characteristics of this new transmission facility,
limited by a metal sheath, can be envisaged. both from the viewpoint of the very great
This type of guide may be constituted by a bandwidth which may be transmitted and
single cylindrical tube consisting, internally, simplicity of the propagation medium, evidently
solely of a dielectric cylinder through which is potentially highly useful.
transmission of the electromagnetic waves is A previous issue of ELECTRICAL COMMUNICATION
effected. Recent investigations, especially the included articles * + by Professors J. Saphores
remarkable researches” ? of engineers of the Bell and L. Brillouin on certain theoretical aspects
Telephone Laboratories, New York, have dis- of dielectric cable propagation. As to hyper-
closed the possibilities of this new method of frequency technique, Les Laboratoires, Le
propagation. In the present article, the results Matériel Téléphonique, Paris, started research
obtained by the American authors are freely on the problems involved in 1929, and it
used with a view to showing their theoretical will be recalled that a demonstration was
relationships with the modes of propagation in made in March 1931 of a two-way radio
coaxial cables. Attenuation values are compared telephonic link on a wave 17 cm in length
for both cases, and in the case of dielectric across the English Channel ® © 7. Interest
cables, these values are compared for each type in the hyper-frequency technique was greatly
- of wave on the basis of the respective frequencies increased by the publication, in 1936, of
which theory indicates would yield optimum Dr. Southworth’s important experiments? on
operating conditions in a cable of given the subject. At a meeting of the Société de
diameter. Physique in Paris, November 18th, 1938, the
Propagation through dielectric guides, pro- major properties of Ey, Hy, H, waves were
vided consideration be confined to cables of demonstrated with an 8 cm wave oscillator,
practical dimensions, implies the use of oscilla- and the propagation of a 2.5 cm wave in a
tions of extremely high frequencies—hyper- dielectric cable 18 mm in diameter also was
frequencies—corresponding to waves only a few shown. The experimental apparatus used on
centimetres in length. Their applications, this occasion will be described in a later issue
obviously, are dependent on the development of ELECTRICAL COMMUNICATION.
*
*% *
* The present paper is based on two articles in Bulletin de
la Société Francaise des Electriciens : The problem under consideration in this
“Théorie des cAbles diélectriques cylindriques et
relations avec la théorie des cables coaxiaux,” by A. G. article starts with the study of the propagation
Clavier, April, 1938. of electromagnetic waves in a dielectric cylinder
“Etude complémentaire sur les. coefficients d’atténuation
dans les cables diélectriques cylindriques et les cAbles bounded by a metal sheath. This study is
coaxiaux,”” by A. G. Clavier and V. Altovsky, September, extended to show the relationship existing
1 For numbered references, see end of this article. between the above kind of propagation and that
276
DIELECTRIC GUIDES—COAXIAL CABLES 277
which occurs in a coaxial cable. Part I is
devoted to general properties and frequency S; So
limits ; Part II to consideration of attenuation fa ¢
/ /
coefficients. ! f
— —_ — —. — — 2
\ O; \ Op
PART I: EQUATIONS—FREQUENCY \ \
LIMITS
Fig. 2.
I. General
In order to determine as a first approximation
the general characteristics of the propagation of gences, and must be used in conjunction with
electromagnetic waves in dielectric guides, the the boundary conditions which are derived
dielectric may be considered as perfect (zero from the fundamental laws of electromagnetism
conductivity) and the sheath as a_ perfect (Ampere and Faraday) and which, in this case,
conductor (infinite conductivity). require that, on the surface between the
An electromagnetic wave is characterized at dielectric and the metal sheath, the electric
each point of the propagation path by a vector vector be normal and the magnetic vector
—> > tangential.
electric field E and a vector magnetic field H
Since the problem under consideration in-
which, under the assumed conditions, are related
volves cylindrical symmetry, the application of
as indicated by the well-known equations :
cylindrical coordinates p, 0, zis indicated. Such
&
ve
BY: = curl
>
H ; (1)
coordinates are represented in Fig. 1, as is also
the positive direction of the angle of rotation.
It will be recalled that if A, , Ao, A, are the
—u
dH
BY: = curl
>
FE > (2)
components of a vector A, the ‘curl components
are expressed by:
e is the dielectric coefficient and py the perme- 1 0A, Ag
curl p A ° 0 _ Je , (3)
ability of the medium involved.
Equations (1) and (2) are valid in both the A dA,
electrostatic and electromagnetic C.G.5. systems curl
» A = se - (4)
of units, as well as in the practical system.
> >
They imply that E and H have zero diver- curl, A = alseé (oA) - SF | 6)
13d 1349. 04,
and div. A = ay (pde)+ © =) + ye (6)
2. Energy Considerations
Let us consider the dielectric volume V
bounded by two cross-sections S, and S, and
the metal sheath (Fig. 2). The electromagnetic
energy in this volume at a given time is obtained
1
by the summation in V of = (cE? + p A).
According to Poynting’s theorem :
I | (Ex H\dS = _2 ~ | (ck? + pH?) dV.
Ax st . Ot 8x Jv 0 ,
(7)
We are only interested in fields which vary
Fig. 1. periodically with time, so that the mean value
278 ELECTRICAL COMMUNICATION
1 >
of the total flux of the Poynting vector i [Ex A]
™ (15)
in a period is zero. There is no flux, however, > >
passing through the metal sheath. The mean As our problem is to find E, and H,, which
value W,, of the flux through S,, Sy, and are expressed in terms of the axial components
therefore any cross-section, in direction 02, is by means of the linear differential equations
constant and gives a measure of the flux of (9) and (10), the solutions can be considered as
energy along the cable. resulting from the superposition of the three
Separation is then indicated of £ and H into
. . . . > >,
following cases :
(a) H, =0 and E, =0 everywhere in the
cross-section components FE, and H, and axial
. > > .
cable ;
components #&, and H,. W,, is expressed by (b) H, =0 everywhere in the cable ;
. —> > .
> > (c) E, =0 everywhere in the cable.
means of F#, and H, only:
° Sl SS 4. Non-existence of wave for which H, = E, = 0
Wm - | sAndik x Has, (8) in a dielectric cable—The coaxial cable
type of wave
and requires 2, and H, to coexist in order to
. > > . .
In case H, and E, are assumed to be zero
ensure propagation along the cable axis. everywhere, equation (5) combined with equation
(10) yields the relation :
3. Separation of different types of progressive ry) o£,
—_(pKF,)
waves Ye (eke) —— —2
5 = 0; (16)
In view of the above, equations (1) and (2)
a corresponding relation applies for the A
may be written as follows :
components.
se > = > On the other hand, the divergence condition
€ - — curl H, = curl H,-« ee D (9)
for the E vector in this case would yield (see
Equation 6):
Tr > > i. P) dE
—u at — curl E, = curl E, + U. at (10) — (pF — =0.
oe (eB) + 00
(17)
Since we are considering progressive waves This means that EH depends on a_two-
—>
dimensional potential U (, 0):
along the axis Oz, all vectors A occurring in our
problem should be of the form
> py = — <5 fet 0m, (18)
A, . f@t-®), (11)
Al ou ilwt — yz).
. >
in which 4, is dependent on coordinates
,
e and E, ~ Je" eer 79) , (19)
@ only.
U, according to (17), verifies Laplace’s equation :
wo = Inf, (12)
v* U =0 (two dimensional) ; (20)
2x Unf
Yu yy? (13) and, since £ is normal to the boundary, U must
be constant on the boundary and therefore at
f is the frequency, >’ the length of wave along all other points, according to a known property
Oz, v’ the phase velocity along Oz. of such potential functions.
Hence There is thus no possible wave in a dielectric
>
cable for which H, and E, are simultaneously
oA ae zero everywhere.
ava =joA, (14)
On the other hand, this type of wave can
DIELECTRIC GUIDES—COAXIAL CABLES 279
exist when there is another metallic boundary then, from (21):
inside the sheath and, in this case, U must be
V =Vei er = 2 [roge eierr9 (29)
constant on each of the boundaries. A well- € a
known instance is exemplified by the coaxial
type of cable, in which the only possible form u,b
“log. =Z; (30)
of the potential U is known to be given by the € a
logarithmic law of distribution : Z is the characteristic impedance of the coaxial
U =-Alog oe + B, (21) cable.
Similarly, the well-known Kirchhoff equations
A and B both being constants.
for the case of a coaxial cable without dissipation
The fundamental properties of this type of
may be derived from the above equations.
wave are easily derived from consideration of
equations (9) and (10). £ and H are reduced 5. Waves in dielectric cables for which
to components FE, and Hy. H, = 0 everywhere (E waves)
Equations (9) and (3) combined yield the From the condition H, =0, the following
relation : simplification ensued in the first two relations
included in equation (9) :
UE
aT oma?
de °?)
22
oF,
ay de 0; (31)
and, from equations (10) and (4),
oH, o£, g ~ - =0. (32)
-—p— = 23
This yields, according to (14) and (15):
hence eu ve = ye 24
(24) Ey =~ Hy = [25 He (33)
The same relation applies for Hg. It shows
that the wave is propagate
[text truncated]