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Page 8 THE TELECOMMUNICATION JOURNAL OF AUSTRALIA TELECOMMUNICATION JQURNAL OF AUSTRALIA
June, 1938 June, 1988 THE
the telephone. circuit worked earth return and>
the power hum was found to be negligible in
_Fading: The received signal varied in inten-
sity throughout the day but the variations were A SUBMARINE CABLE TRACER G.N. Smith,
the telephone when suitably balanced condensers in all cases of slow period and no distortion was The +
were used. . It is almost a platitude to state that submarine tween two unlike magnetic poles.
noticed even when the received field was. rela- It is therefore im- paths may be considered as parallel to th
tively low. At no period during the tests was -eable repairs are expensive.
Results of Tests: portant that every effort should be made to except near the fault and there are equipc
General: there a complete absence of signal when trans- surfaces perpendicular to these paths, tha
Receiving tests were made for a facilitate repair work and to make best use of
mitting and receiving on the horizontal aerials. right angles to the cable.
period. of 11 days, from 29/9/87-9/10/37 using the time for which the repair ship is chartered.
both horizontal and vertical aerials. _ Fig. 9 shows a curve of received field inten- is the principal cause of delay, Any two electrodes in the current pat
As bad weather
When transmitting on the horizontal aerial, sity during typical listening periods, and it is
any means of using this time to assist the repair have a potential difference between the!
of interest to note that the maximum variation This can often be done vided they are not both in an equipotent)
expected due to transmitter fluctuations was ig well. worth while.
The measurement of potential. ¢
20)
with the apparatus about to be described. face.
approximately 1 db. — consequently made along the line of these ¢
When a submarine cable is laid, its position
deflection being ol
¢ muilhwatt.
Effect of weather, time of day, ete.: During is carefully charted and splice sheets are pre- paths, the maximum
It is not necessary
\ the period of the tests the weather had no
noticeable effect, but it is possible that seasonal
‘ pared
percentage
to show the position of
of slack laid over various
splices and
portions
the
of
when
ever,
over the cable.
in practice for the electrodes to be
changes may be noticed. This will be investi- the route. Owing to tides, currents and sub- exactly along the line of the cable, any ¢
gated by long period observations on the channel. it is possible for a cable up to an angle of 40 degrees beingge
>
to
marine disturbances,
5
The signal intensity at night appeared to-be change its course or from satisfactory. A correction is then applied
to be moved and so
relative
the same as during the daytime, the fading similar causes it may be buried. Naturally, ing multiplied by cosine of angle of defl
g..
noticeable on broadcast and high frequency pro- ' either of these effects would increase the time
pagation being absent. of grappling unless some means is available for
a6.
detecting the true course .of the cable-from the
IN Summary: The tests indicated that communi-
repair ship.. This facility is provided by the
Output
N\ cation is possible over distances greater than
¢
IN N optical when using a frequency of approximately Submarine Cable Tracer which. will also show
40 megacycles per sec. but the long period re- the actual position of an earth fault, thus acting |
So.
0 (0 20 30 30 sd 60 90 fo GO “fro liability of such a circuit has yet to be estab- as a confirmation of shore tests. It is particular-
Input im db relative to'artitrary level lished. The present intention is -to instal at ly useful when land sights are not available for
Fig. 8.-Super-regenerative Receiver Noise Level Stanley, Tasmania, a transmitter of 200-800 navigation.
plotted against signal input.
watts power and to take long period recordings Such equipment has been developed by the
the received level was approximately 30 db better Research Section of the British Post Office and
on the horizontal than the vertical aerial. How- has been applied to our own requirements for
Nore wo
ever, when transmitting on the vertical aerial, work in Bass
Strait, both on the telegraph and LEAVE PIETER SWITCH ON” ONLY DURING READINGS
smicrovoit.
the received signal was only 10 db better on the telephone cables. The essentials:
are a low fre- Fig. 2.
vertical than the horizontal. Occasionally when quéney generator and a pair of search electrodes
using the vertical aerial for transmitting, the to reduce the observed reading to a di
along the lie of the cable. As the sh:
received signal was almost as strong on the the cable towards the eart
gresses along
above
horizontal as on the vertical aerial. This would
indicate that a change of the plane of polariza- the deflections increase rapidly as the’ f
approached and cease abruptly beyond it.
Tues day. |5-10-137 Horijon te. Rena ds
tion was taking place—propagation favouring
~The electrodes may be towed “in line” al
db
horizontal polarization. #44, A
fathoms behind the ship or, as is now pr
mtensity
Aerials: Horizontal polarization (horizontal ¢40 _—-—— \ 4
by the British Post Office, “abreast” of 1!
aerials) proved to be consistently better than M \ by booms’ over the side so that they ai
vertical polarization, the difference at all. times £36
In_ the
line at right angles to the ship.
Signal
being at least 20 db in favour of the horizontal. 432
a7 72 roo, case it is necessary, of course, for the
In preliminary theoretical investigations it was — oer
Hors ontal| Mertays
cross and. re-cross the cable approxima
thought that the horizontal aerial would radiate Wed. |G:1037
right angles. . a
a large proportion of the energy at high angles Fig. 9.—Varlation of sveceived signal intensity
to the horizontal (the calculated maximum en- ’ over typical listening periods. - These electrodes consist of two _bré
ergy was at 18° to the horizontal). The high rotators shorn of their fins, with a sep
of the field strength received in Victoria. The of 10 fathoms between electrodes. El
value of energy at an angle to the horizontal is
caused by wave interference between directly transmitter will be crystal controlled to prevent ot Fig. 1.—Cable Tracer Equipment.
contact is. maintaine d by means of cab-ty
propagated radiation and radiation reflected from any appreciable frequency change, and the re- Which are connected a tuned amplifier and In-the case of the “in line’ method the t
the ground, and the above figure of 18° was ob- ceiver will be a superheterodyne type in which alvanometer, these being shown in the photo- is connected to a draw-bar spring and tl
tained assuming a flat earth and perfect re- the automatic volume control voltage will be used _ raph herewith. It has been shown that the trodes are weighted, thus preventing
flection from the earth. At Tanybryn, however, to control the current. through a triode tube movements and consequent spurious def
the ground sloped downwards away from the operating a recording milliammeter. Horizontal on the amplifier galvanometer. The B.
_ array and dropped suddenly about 100 feet out, aerials will be used at both the. transmitter and now experimenting with electrodes whic
so that the flat earth theory would not apply receiver. deeper as the towing speed increases tl
accurately, and an increased signal in the hori- Recently the transmitter and receiver were ducing the tendency for the electrodes t
zontal. at the expense of high angle radiation completed to provide an emergency service, but fault (or earth connected to far end of surface. It has been shown that the sen
would be expected. the tests will be continued. in a fashion similar to lines of force be- of the method is independent of the dept