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BDULLETIYN
TASMANIA DIVISION
APRIL 1975
President: R. Eamett VIITKX
Secretary: J. Gelston VK7ZGJ, G;P.O. Box 1010, Launceston. 7250
Treasurcr: v, Carter VK7AK
oditors B. Yeonan VK74BY, ¢/~ Department of Transport
Launceston firport, Tas. 7250 Ph, 918218
e A RB e A3 P e e S e
NOTICE OF IWETINGS
Mays 3rd Council Meecting,QTH of VK7ZBY Launceston Airport, 2.00 p.rve
7th Southern Branch,special General Meeting, QTH of Tom Allen,
VK7iL, 8 p.n.
- ‘ ‘
9th Civil Defence Building, Bourke Street,
Northern Braanch,
Launceston, 8 p.ile ‘
13th Worth-est Branch, Lakins 7Tall Ulverstone, 8 p.m.
EDITORTAL
Well Gentlenmen, another finnual General Meeting and Dinner has come
and gone. It cannot be said that members attended both these functions
in force, in fact the total number of members that even bothered to fill
in their ballot papers, was to say the least, disappointing. I don't
know what the reasons are for this apparent lack of interest,in
Divisional matters, but it can do nothing but create dissatisfaction
anongst the members vho are trying to do their best to keep this Division
a vibrant and viable one.
I call on all members of this Division to back their Branches end
Divisional Council in all matters to ensure that this year, will be the
year when the VIT7 Division becomes a united and active cne,
73, Brian VK7ZBY
STXTH ITVTELSAT TV IIOW Tif ORBIT.
inother Intelsat IV comunicaetions satellite = the zixth in the series,
and the second to be placed over the Pacific - has been launched from
Cape Canaveral, Florida.
The satellite, designed and built by Hughes Aireraft Company of
California, was launched by N,.\,S.A. for the International Tele-
Communications Sateliite Organisation, An Atlas Centaur booster was
used to place the satellite in synchronous orbit 35,300 km, above the
equator, and one degree from the International Datelinc,
The new Intelsat IV will provide added capacity and back-up assurance
for the primary Pacific satellite, launched in January 1972, It will
become part of a "neck-=lace" of Inteleat IV's orbiting the globe, Three of
these are over the .Ltlantic Ocean, whilst ancther is over the Indian Ocean.
Reprint Electronics justralia - March 1975
2,4
REPORT CN 1975 ANNUAL GENERAL MEETING
On Saturday the 5th of Lpril the VK7 A.G.M. was held at the L.E.B.’
Rooms, High Street, Launceston, with 34 members and one visitor present,
the visitor being Bill VK3ZIK.
The meeting opened on time with Reg Emmett VK7KK in the chair, and
Steve VK70A, as secretary. After the reports from trth the President
and Treasurer were presented, (a copy of the Trecasurer's statement
appears at the cnd of this report) the matter of electing Divisional
Councillors for the ensuing year was carried out in the form of a ballot.
The result of that ballot is as follows:
1. VETIK Bill Carter 5 VKTTB Mike Jemmer
2. VKTKK Reg Emmett 6. VK7ZAQ Graeme Rand
3. VKT{PF Peter Frith 7« VK7ZBY Brian Yeoman
4, VKT7ZGJ Joe Gelston
The election of other office-bearers then took place, and they are;
Patron: VK74G J. Milne
QSL Manager: VKiCH C, Harrison
Legal Officer: VK7RR B, Morgan
Bulletin Editox: VK7ZBY B, Yeoman
Key Section Co-Qrdiaators VKYRH R, Harwood
Intrudsr Watch Co~Crdinators; VIR 1. Tvor
Y.R.C.S. Supervisor: VK7EX R, Imnett
Historical Qfficer: Council to take care of this in the
ensuing year, and to establish a
pernanent location,
VHF' Representative; VK772¢3 J. Gelston
Juditor: Council to handle
Oscar Co-Ordinator: TK7PF P, Frith
Membership Secretary: VKTZMK 1, Kaott
WICEN Represcntative: VK7V J, Van Staveren
- After these pogitions were filled, the mceting moved into the two
motions on the agenda, as per the larch Bulletin. The result of these
motions weres
1. The motion concerning constitutional amendments was passed with
no amendment,
2., The motion concerning the VK7 Merit /ward was passed with one (1)
amerdment, that being that wherever the word "member" occurs, it
should be changed to "pexrson",.
With the passing of “t%easc two motions the 1975 A.G.M., closed at
1600 hrs.
General Mceting
A General Meeting of the VK7 Division followed the A.G.M., and
started at 1610, with the following resolutions made with regard to the
laid down agenda.
1, On the subject of books and magazines at present held by the
Southern Branch; they are to be retainedby the VK7 Division
and Council will ~ssume care and control of the said books and
nagazines.
3.
A.G,M, REPORT (Contd.)
e On the subject of equipment held by Branches - the Division is to
retain the Tz transmitter and associated equipment for broadcast
purposes, and that the remainder of the equipment in the Southern
Branch become Southern Branch property with one amendment - that
should the 3Southern Branch vwish to dispose of this equipment, that
it be advertised as a Tender in the Divisional Bulletin,
Be The next item discussed was that of Branch 4A.G, M. uniformity. It
was resolved thatif Council recommends it, all Branch A.G.M,.s will
be in March,.
4, In the area of discussion instigated by Branch Presidents, it
appeared that all Branches vere quite happy with the present
relationships between them and the Division.
5 The Bulletin Editor gave a brief rundowm on the Bulletin costing,
and stated that »roviding things remeined as they are, the yearly
cost of the Bulletin should be around $100, The Editor also asked
for comments from the members on the present Bulletin format, bi-
monthly posting, ctc. as it is difficult to know what the members
are looking for in their Bulletin without feedback from then.
6, On the subject of broadcasts, members present at this meeting
gave a reassurance that they were quite happy with the system as
it stands at present, and asked that the people concerned with the
Sunday morning broadcasts vhether originating or re-broadcasting
be thanked for their efforts in the past and the future.
T There being no other business, the General lMeeting ciosed at
1700 hours.
At approx. 1930 hours the Annual Dimmer of the VK7 Division got
under way at the Village Motel Launceston with 44 persons attending,
4L very enjoyable dinner, which wvas washed dowvm with a selection of
excellent dinner wines, was very suitably disposed of, and judging by
the reactions and anticg of some nmembers, and their wives presemt, the
1975 lnnual Dinner was a rip-roaring success. The only comments I have
to make is to thank the organisecrs for their efforts in ensuring that
the whole show, including the £4,G.i. progressed smoothly; those who
did not attend this marvellous dinner were the ones who missed out.
73, Brian VITZDY
AATEUR RADIO EXIIBITTON
- The dates for the fmateur Radio Exhibition at the Northern Regional
Library in Launceston have been finalised. The exhibition is to be held
from June 9th to June 21lst inclusive.
Norm VEKTNR, who is organising this display would appreciate any
equipment that you feel would be suitable for this exhibition.
As the exhibition is to be get up on Saturday the 7th June, the
deadline for the équipment will be the last week in May to give Norm
and his helpers tine to see how the display is going to fit together.
For further details see your October Bulletin on this subject.
EDITOR
4.
Wel.h. TASIANTAN DIVISION:GENERAL ACCOUNT
: FEBRUARY 1975
Balance Brought Forward $ 336=63
General iccount Inteiest 15-36
Term Depogit Interest 78-00
Dénations Life Members 44-00
Subscription Collections 66-00
Refunds Federal Executive __T113-174
1313-73
Expenditure
Petty Cash Sec. $ 5=00
Wreath 10-00
Convention Expenses '73 98-52
A.R. Inserts and Advertisements 24-44
A.R, Losses to VI(3 116--00
Bulletin Expenses 102-28
7 W,I. Licences 12--00
Stamp Duty Constitution 200
.Refund Interest Southern Branch _ 234-00
Travelling Expenses S, Fraser ' 18-75
Share Surplus Funds N.W. Branch 38-00
Subscriptions to E.D.P. Rep. | 66-00
Unpresented Cheques as at 22/2/75 54380
forYear
- Surplus 4204
1313-73
Treasurer: 3,W. Carter
Auditor: D.H, Fisher
fuditor's Note: Monies from Federal Executive not readily
reconcileable with documents received, and have taken these as
presented,
Equipment lccount stands at $28-00 and is to be transferred to the
General Lccount,
5e
MEETING NOTES
Council
: February/March
The PFebruary Council meeting was held on Saturday the 15th, at the
QTH of Peter, VK7PF. Apologies were received from liessrs, Yeoman and
Raud. After the minutes of the previous meeting were read and
confirmed, the subject of Divisional equipment held by the Southern
Branch was discussed, The Southern Branch will be approached with the
iew of asking that Branch to do a stocktake on Divisional equipment,
at present residingin that Branch,
Included in the correspondence was a ifomination Form for Federal
Councillor from Peter VK7PF, As this was the only nominatiom received,
Peter was clected Federal Councillor for the ensuing year 1975, Also
tabled in correspondence was the report on the 17th J.0.LA.
The Council discussed the subject of the Merit Lward and resolved
that it be included as a Yotice of Motion for the 1975 A.G.M.
2 ARe
The March Council meeting was held on Saturdey the 15th at the new QTH
of Reg VKTKK. Present were Messrs, Frith, van Staveren, Fraser, Rand,
Carter, Yeoman, and Emmett, After the minutes of the previous meeting
were read and confirmed, Council nominations were received from VKPs
LK, JV, FB, ZAQ, Z4BY, KK, PF, and 4GJ.
Six applications for membership were received from the followings:
3tephen Russell, of Ulverstone, for student membershiy-
Stanley Burtt, of Devonport, for associate membership
ALlan Holmes, of Launceston, for associate membership
James Davis, of Latrobe, for associate membership
Bernard Turner, of Burnie, for associate membership
John Wicks, of Ulverstone, for associate membership
sfter due consideration, all of the above were passed for
membership, The Council welcomeg you all to the VK7 Division.
As this is the last Council meeting for the year, the Commecil
weuld like to thank the Branches for all their co-operation during
the year and hopes that the incoming Council will receive the same
co-operztion., See you all at the L.G.l.
73, Brian VK7ZBY
Northern Branch : Hebruary/March
The February meeting of the Northern Branch was held as per usual
in the 4.6l.B. Rooms, High Street, Launceston, with thirty members
present, an improvement on the January meeting,
The meeting was informed by Ed, VITTHE, that discussions with the
Launceston City Council on the subject of Clubrooms were still in
progress., Further details will be made known when available,
The meeting was then informed by Peter, VK7PF, that in line with
the Department of Transport's 80 per cent cost-~recovery programme,
power charges will now be made for the Mt. Barrow repeater VK7RLL.
After discussian, the meeting agreed to pay the $32 per year for power,
and the $35 per year for the facility of having the repeater on standby
emergency power,
6e
MEETING IOTES (Contd.)
The Editor of the Northern Branch's Bulletin (QRM), John VK7JV,
indicated that he would be resigning from this position and that a
new Editor would have to be found to:fill the position., I know I
speak for all of the Northern Bfanch, John, when I say thank you for
a job well done.
The mecting was then presented with an excellent talk by Ed Bovis,
VKTED, on Barly 3éa~faring Radio, in the days when spark transmitters
and sailing ships were azll the rage. Bd went into the problems that
an operator of a spark transmitter had to contend with, such as, after
every transmission a new spot had to bz found on the Crystal Detector in
W#o Receiver, because it had been burnt out by the transmitter., The
approximate pewsr output from these transmitters was 1.5 kw, Ais
technology improved, the range wag increased, and with better receivers
and transmitters, break-in operation was possible, After hearing your
~talk on early sea-faring radio, and the problems encountered, I think
we can all appreciate the advancements made in the field of communications.
From all those present, many thanks Ed, for a most informative talk on
a most fascinating subject.
The meeting cloged at approximately 2230 hrs, for the usual
rafreshnents anda eyeball 0S0s.
73, Brian VK7ZBY
Te e1 e AT e
¢ March cow the A,G.M, for the MNorthern Branch once moro and this
enticement produced a roil up of 36 members,
Prior to the election of 0ffice Bearers, sewsral items were
brovgat up. As John, VK7JV, was relinquishing his post as Editor of
QRM, a general vote of thanks was passed by the meeting for his
tremendous effort in the past. We wish the new Editor, Graham, VK7ZGG,
the best of Iuck with his new venture,
A point raised by Fd VKTED, was whether all technical articles
published in QM and Bulletin should be forwarded for publication in A.R,
Of several ideas put forward, it scems that the greater percentage are
not of gufficient technical standard and/or there is such a delay in the
articles being published in 4.R. that duplication would not really
matter anyway.
The President Reg, VK7KI, then tabled his /Annual Report, followed
by Kevin VKT7ZAI, who presented his trading account for the equipment
store.
The election of office bearers for 1975 then followed, These are:
Presicdent: Brian VKT7ZBY Lecture Officer: Wally VK7ZWX
Vice~Pres, l: ILindsay VK7ZLD QSL Officers Col VKTLZ
Vice~Pres. 2: Reg VKTKK Branch
Secretary: 3 VKTHE Correspondent: Bob VK7ZRF
Treasurer/ Refreshment
Equip. Stores Kevin VKT7ZAH Officers Reg VKTKK
QR Editor: Graham VK7ZGG Luditors Carl Waldom
The Annual General Meeting closed at 2015, to be reopened at 2025
for a General }Meeting by the new 0ffice Bearers.
7.
MEBTING NOTES (Contd.)
Alan Holmes was welcomed as a member to the Worthern Branch.
Id VK7HE, reported no new developments on the Clubroom investigation.
He also requested that people intending to attend the Divisional A.G.IM.
and Dinner on the 5th /ipril please let him or Kevin VK7ZAH, know before
the deadline, the lst Lpril,
Finally, Mr, John Hodson, an engineer with the P.M.G. gave the meeting
an informative and at times amusing lecture on the transitién from black
and white to colour of the Jational Television Transmitters, in particular
the Mount Wellington station,
It appears that amateurs are not the only ones that emit spurious
radiation from their transmitters, even if it is 60db dovm - on 20k or
200kw B.R.P,
73, Bob VK7ZRF
Southern Branch
:April
At the April meeting of the Southern Branch, held at the QTH of
Tom Allen VK7AL, only nine members were present, and although this did
constitute a quorum, it was decided not to proceed with the main
business, the election of office-bearers for the coming year. The
recasons behind this decision were several, Firstly, not enough
nominations (or volunteersg) were received for the vacant positions,
Secondly, in view of the seeming lack of interest, it was questioned
as to whether the Branch should be continued, so it was decided to
attempt to canvas the opinions of as many members in the South as
possible, before anything further is done, Until then, we still have
last year's office-bearers.
In order to determine the feelings of members, and amateur non=
members, a special General Meeting is to be held at Tom Allen's QTH,
22 Xaroola Road, Lindisfarne, on Wednesday llay 7th, at 8 p.me As
stated, all members interested are asked to come along, and as many
amateurs who are not members will be notified - the Branch has funds
and equipment, and only a small groun of those who are aware of it
seen interested in using them, Perhaps there are others who could use
them also, possibly much nmore effectively. As a background to the
gpecial General Meceting, the following is a brief summary of discussion
heard at the April meeting, and of the state of the Branch at present.
It was genecrally acknowvledged that interest in the W.I.A. in the
South has been declining, as had the interest in radio generally; both
T and VHF operators scem to be less active (on the air, at least).
Many people expressed opinions as to the reasons for the decline; these
included the fact that W.I.i. meetings held no interest for members;
they had no interest in procedural matters and they found nothing else
at meetings, Some lectures and social activities were organised, but
the lack of support was disheartening to the organisers, giving them
no incentive to go on. A lack of interest and support was also the
reason for the lagging activity in group projects, mainly the new
repeater.
L suggestion was made that the Branch should hibernate for twelve
months or so, but such a decision could not be made with so few members
present,
8.
MEETING NOTES (Contd,)
The state of the branch is probably reasonably well known to most
members, and the following is just a brief summary. There are several
projects and activities which are being carried on mainly by a few
interested members, on their own, and with little interest, encouragement
or support. These include the Saturday morning Y,R.C.S. classes, which
are going extremely well although the interest is about half a dozen
members and a couple of interested non- members, The Divigional
broadcasts once every three weeks, and the re-broadcasts every week -
again a few interested people keep it going, but their efforts are
hardly rewarded by the numbers checking in on the callbacks, especially
on VAF, The last project is the construction of the repeater - to date
only about four people have shown much interest, and they have done all
the work so far, although several new faces have expressed a great deal
of interest lately. This group is working under its own impetus,
Finally, the state of the Branch finances: we are running an
equipment store which has been very poorly supported in recent times,
even though priceg ou the range of items stocked have been very good.
The equipment store has been financing the repeater projectto date,
although with miserable turnover; is making quite a hole in the funds.
The clubhouse funds stand at about $3700, mainly in fixed term deposits,
all of which will mature by August 1975. We have had several offers of
land on which to build a clubhouse, one of which would be more than -
suitable in all respects, if the offer is gtill open. Assuming then,
~that we do not have to buy any land, the clubhouse funds at present
will go a long way towards providing material for a building.
These then, briefly, are some of the items which will be brought
foward: should be maintain the Southern Branch, and support the various
groups and projects already struggling along? Should we start on something
new, which will have the support of more than just a few? Or should e
let the Southern Branch die a natural death, in the hope that perhaps,
at a more fertile period in the future, it may rise again? Interest in
radio and electronics is still strorg, on an individual basis - people
are gtill sitting for their £.0.C.P, and the Y,R,C.S. has many keen
young members; perhaps, if the W.I.i. in this area can re-aligm itself
to promote radio and electronics, for individuals and groups, then we
may be able to do far more good and interest more pcople, than we have
in the past. It is hoped that the meeting on Wednesday May 7th will
discuss and hopefully resolve many of these points, and conclude with a
concrete plan of action for the future.
If anyone is unable to attend this meeting, for any reason, and
has some ideas or opinions, these will be well received by either Phil
Thompson VK753, or Andrew Boor VK7AW, verbally or in writing, prior
to the meeting. But everyone who has any interest at all, no matter
how slight, in the W.I.A, and radio, is urged to make an effort to
come along to Tom's place,
Signed: Andrew Boon VKTAW
Phil Tompson VK7SS
e — .S o e
REQUEST FOR A MISSING DOSSLEER
Fron liike Jenner VK7FB comes a request for the dossier that was
compiled and written by the late Lon Jenson VK7LJ, on the VK7 Division
since ite inception. Anyone having this dossier, or knowing of its '
whereabouts, please contact Mike on one of the following phone numbers.
Work: 441611
Home: 473729
9.
CALCULATIONS
-
OF WIND 1,0.DING ON TO.JER AU'D ANTENI, STRUCTURE PIRT 2.
Reprinted extracts from Ham Radio, jugust, 1974
Mg 3
Uniform wind
force. 7.32 1lbs
per foot.
292.8 1b. s
10, -
477.6 1bs,
238.8 1bs,
Fig. 5B
40 FT,
11,
GuyingofTowers
Guyed towers have the advantageof requiring much less structural
material than self-supporting tovers. As an example, a gelf-supporting
700~Foot (213.4 meters) steel tower of conventional design, will teigh
about 460,000 1lbs. (208,651 kg.). A4 comparable guy tower will weigh
about 200,000 1bg.(90,718 kg.) including the weight of the guys. It
should be remembered that a guyed tower nmust also be capable of
gupporting the guy-wires. While very few amateurs are so fortunate,
or unfortunate, as to have a 700-foot tower, the sevings in material
of a guyed tower is obvious.
Assume now the sanc 40~foot tower and antenna array as previocusly
described hag a set of guy :' g 30 feet (9.1 meters) from the base of
the tower, as shovm in fi-b. érou the Pythagorean theorem the length
of the guy wire is : V40° )O
+ = 50 feet (15.2 meters) . The
angle with regpect to ground iss :
olc
wls
© = tan = 53,1 degrees
For the sake of simplicity, we will congider only one guy wvire,
This is ectually the case vhen the wind is blowing toward the tower
from the direction in which the guy wire under consideration is
anchored. ‘
It is notgenerallyappreciated, but a guy wire converts an over—
turning noment 1nto increased dovnvard streuss on the tower, As previously
noted, the total horizontal force in this exanple is 293 1lbs, (132.9
kg.) on the towver plus 92 1lbs. (42 kg.) on the antenna. Since the top
of the tower is nov constrained hy the guy wires, the overturning moment
is zero, Ior this reason the structural requirements on the towver
and foundation are grecatly reduced because these items need on support
the weight of the assenbly and the additional load imposed by tension
in the guy vires.
rige T
146.5 + 92 = 238,5 1B ————> E
' WID FORCH,
{ /.‘
40
T1
MAST
D
12,
Because the horizontal force on the tower -~ 293 1bs.(132.9 kg.) -
is uniformly distributed over the length of the tower, we will assume
that one-half the constraining force - 146.5 lbs. (66,5 kg.) - is
located at the top of the tower and one-half at the bottom, The
horizontal force on the antenna - 92 1lbs, ( 41.7 kg.) - will be assuned
to be located entirely at the top of the tower. This isshowm in Fig.
7. )
This allocation of reactions given may seem arbitrary, but it is
difficult to visualize a mechanism by which the 92 1b. (41.7 kg.)
horizontal force of thce antenna can be transmitted to the base of the
tower without generating a moment. 4lso, if there is any error, the
forces in the guy wire will be overcsgtimated and not undercstinated.
The tension in the guy wire may be resolved into a horizontal and a
vertical componcnt., The horizontal component must be 238.5 1lbgs. (108.2
kg.) since it must exactly equal the horizontal windload (146.5 + 92
1bs. or 66.5 + 41.7 kg.). The tension in the guy wire itself may be
calculated by setting up a vector diagram as in fig. 8.
v“ =
238.5
e e
- .2 bS.
Te sin 35.,9° 331.2 1
Hor., wind force = 238,5 1R,
o los.7 _
Pev= 4in 36,90 = 181 kg.
where F gw is the force on the guy o 1 9 m 3
wvire and the additional vertical Z;E;;g;it iin31on
conponent vhich must be resisted resisted vgriuy
by the tower is: by tower 397.2 1B.
238.5 Z71 0
318 LB.
Pv = tan 36,9° = 318 1ba.
Fig. 8
i 2082
}1 v - 'tal'l 36,90
& Vs &
- 14‘4.(— lx.gn
In other werds, an 86.6
nph (139.4 kph) wind will
develop a tension of 397.2 1bs, ~
(180.2 kg.) in the guy wire and
an additional vertical load of
318 lbs. (144.2 kg.) on the l
tower.
This vertical load is more than the weight of the antennal It
should also be emphasigsed that these loads are in addition to the vertical
loads caused by the initial tension in the guy wires.
So far we have considered the inwolvement of just one guy wire, Then
considering two guy wires you night think that for the same horizontal
wind load, the tension in each guy wire would be one-half the tension for
one¢ wire, Unfortunately, it docs not work out that easily. Let's
considered o towver held by three guy wires at 120° intervals, as shown in
Fg. 9. This is a typical arrangement. If the wind blows in the direction
of arrow "A", guy vire number 1 takes the wind load and the situation is
as explained for one guy wive, If the wind blovss as shoom by arrow "B",
© things are slightly different, as showm by the vector diagram in Fig. 10,
Using the same numbers as in the cxample above, the horizontal wind load
of 238.5 1bs. (108.2 kg.) is shared equally by guy wires 1 and 2, so we
allow 119,3 1lbs. (54.1 kg.) on each. In this case the third guy wire
carried none of the load., The horizontal force in the direction of each
wire is thus ) 119,
ey e B, = COZ Zoo = 238.5 1bs.
B, =” 241
ezo = 108.2 ke.
13 ™Mg. 9
120 ( {Townr i
/
\
Guy wire
1 p
Wind
veetor
.[.L
Wind
vector
B.
As in the preceding example, the ftension in each guy wire is 397,2
1bs, (180.2 kg.) and the vertical componcnt of each guy ‘ire is 318 lbs,
(144.2 kg.) = a total of 715.2 1lbs., (324.4 koo)e The total is thus
twice the vertical load gencrated by a vind bloving in the same direction
ag any one guy wire, It is casy to sce thot windloads can add up pretty
quickly! The use of guy vires inposes a penalty in that the tower and
foundation must be designed for greater vertical loads. he advantage of
guy wires is that the tover and foundation need not be degigned to resist
an overturning monent,
in inportant factor to be considered in the installation of a guyed
tower is the initial tension in the guy vires. If the guy ires are too
loose, the tower will say excessively. If the guys ave pulled too
tightly, an excessive vertical load may be put on the tower, In fact, in
large installations it nay be possible to buckle the tower with excessive
initial tension, It is therefore neccssary to compronise between stiffness
and reasonable sized gstructural nenbers in the tower.
Because of the increasing intercst in 1250 khz. and above, and the
cagy availability of parabolic antennas with solid reflectors, it is both
intercsting and instructive to apply the above principles to a parabolic
dish and conpare these with the tower., We will assune a dish with a 10 FT.
(3 neter) diaueter and a 100 nile-per-hour (161 kph) wvind. Fron equation
1, the wind pressure causced by 100 nile~per<hour wind is 40 1bs. per sq.
ft. The projected area is:
2 2
~TgS =77(10)" = 78.5 sq. ft.
4
and the total horizontal wind pressure is:
2
(78.5 ££.°) x (40 1b/ft°) = 3140 lbs.
If a 10-foot (3 neter) antenna is to look at the horizon to see a
rising satellite, as showm in Fig. 11, the nounting structure nust be
at least 6 foot tall to provide a ground clearance. Thus, the nininun
overturning ncment vill be
(3140 1h.) x (6 feet) = 18,840 1lb-ft,
Note that a ten~foot parabolic dish mounted on a 6-foot gupport has
approxinately tiice the overturning monent as a three-clenent 20 neter
bean, nounted on a 40-ft. tower.
14. Fig. 10
Resulting guy wire
tension 397.2 1b.
One half of the
total horizontal
wind force.
23805/2 = 11903 lbc
side force cancelled by
guy wire No., 2 (in this exauple)
Unfortunotely, this is not the vhole story. The above calculations
are for a head-on .ind, Experinents have showm that the greatest wind force
on a parabolic antenna occurs not for a head-on condition, but vhen the
i7ind is blowing at an angle to the antenna axis, as shown in Fig. 12.
wind
direction
e
— v - — ——
10 ft. antenna axis
A/ -~
nounting ht.
//
abont 6 ft.
Tor most antennas this wind angle is approxinately 560, and the
naximun force is 10% higher than for a 0° wind angle. The reason for
this is that at sonme wind angles the rear surface of the dish acts os
an air foil, which develops LIFT in a sinilar manner to an aircraft
vring, thereby increasing the horizontal force on the antenna.
Because this extra force depends on the shape of the antenna, it
nay not be the same for all parabolic antennas. The antenna peraneter
that has the greatest effect on this additional lifting force is probably
the focal length of the antenna as this determines hov deep the dish rust
be for a given diameter, and hence will affcct the LIFT/DRAG co-~efficient
of the dish. It is not practical to give 1ift co-cfficients or angles
of naxiiunm wind loading for all cases, but a 10% increase in wind loading
due to 1lift at an angle of approxinately 56 isg proabably a good
apprxination for most parabolic antennas,
The relatively large vind loading of a parabolic dish can be
considerably reduced by perforating the dish. If the holes are snall
conpared to the wave length of operation, the effect on antenna perfornaance
will be negligible, but the wind loading will bhe decreased considerably.
15.
Sunary
In the above naterial it hag been showm how to calculate the over-
turning nonents coused by vind forces on antenna structures of the type
used by nost anatcurs. These forces can be appreciable, especially
vhen gugnented by ice. Perabolic cntenncs have cven higher wind loadings.
The use of guy wires has alse been discussed, and it has been shovm hovw
these elininate the overturning unonent but increcse the vertical loads on
the tover,
The procedure for calculating the wind loading on o coaventional
towver/antenna conbination noy be swinerised as follovss
1. Calculate the projected area of the tower.
2e LApply the appropricte correction factor for cylindrical gurfaces
and/or trianguler or crossesections, as necessary.
3 Determine the naxinun expected wind velocity.
4, Calculate the horizontal force on the tower.
Se Deternine the effective area and horizontal force on the antenna,
5 If the tower is guyed, calculate the tension in the guy vires due
to wind londing and determine the additional vertical loading of the
tover,
7. If the tower is froe staending, deternine the nonmente on both the
tover and the antenna separately, and add.
The wind locding on a parabolic dish is calculated in the sane nanner
ag on any other structure, but naxirwun vind loading will occur at an
angle to the nain antenna bean and the numbers will be gurprisingly high,
Towers, like people, can carry only a linited load before they start to
sway. A good nan knows his owm lindt; o good anateur knows his towver
linit.
R— eAO e P LO S S s T AL
Council liceting llotes : Decenber Only
The Decenber neeting of Council took place at the QTH of Steve Fraser
VK704 on Seturday the 1l4th, Present wvere liegsrs. Emett, Rand, Frith,
Yeonan, Fraser. ’
Due to an error on the part of the Bulletin Iditor, the Nouination
Forn for Federal Councillor for 1975 will apnear in the Feb. Bulletin
along ith the Nonination Form for Divisional Councillor, The Editor
regrets any confusion caused by thig error.
One menbership inquiry wias received and that person w/ill be sent all
the relevant papervork in due coursec.
Peter VKT7PF, gave Council a rundovm of the cost of the 1974 Federal
Convention together with the total figure of §2359. Inyone wishing to know
further details should contact Peter.
Unless something urgent comes up there will be no January Council
Meeting. - The next meeting of Council +will be on Saturday the 15th February,
at the QT of Peter VK7PF, 181 Punchbowl Road, Launceston, starting 2.00 pn.
73s, Brian 7ZBY
B -
¢ Q0 o N
AMENDMENT TO OSCARS € 11D 7 ORBIT DETATILS
The following should be inserted in the previous list that was
published in your February Bullctin,
These times refer to the first orbit of cach day and will correspond
to the Orbit details thatappear in the A.R. predictions. To usethese
amended details find the time in the 4.R., lietings which corresponds to
this amended list. The details of thatf day's orbits then follow the orbit
details as published in the Pebruary Bulletin,
73, Peter VK7IPF
e . AP
DAY U0, TIME Z DEG. W. 24 110, TIME Z, DEG. W,
1 0125 069 13 0055 061
2 0025 054 14 0150 075
3 0120 067 15 0050 060
4 0020 052 16 0145 074
5 0115 066 17 0045 059
6 0015 051 18 0140 073
7 0110 065 19 0040 057
8 0010 050 20 0135 072
9 0105 064 21 0035 056
10 0005 049 22 0130 070
11 0100 062 23 0030 055
12 0154 076
VKT NEWS BROLDCAST ROSTER 3 APRIL ~ SEPTIMBER 1975.
ORIGINATING STATION || RE~BROADCASTING (JORTHERI BRANCH)
DATE AND BRANCH STATION -
CH48-801, 801- CH 48
April 20 VKM S VKTZBY
27 VK7ZGF W VIZTGW
Nay 4 VKTTT W VK7ZWK
11 VKTAW S VK7ZDY
18 VK7ZBY ¥ V7TV
25 VKTAX W ‘ VKT7ZWX
June 1 VK7TH S ' VK7ZBY
8 VKK 1 VKTNR
15 VKTKH W VK7ZWX
22 VKTAW S VKT7ZBY
29 VK7ZGG O VKTKK
July 6 VETMX W VIKTZWX
13 VRTTH S VKTEK
20 VK7ZGJ N VETGW
27 VRTTT W ‘ VK7ZBY
Aug. 3 VETLW S VKTZWX
10 W7Z2BY W VK7IV
17 VKTAX W VKT7KK
24 VRTTH S ! VK7ZWXK
30 . VKTKK N VKT7IIR
Sept. 7 VKTKH NW ' VKTZBY
14 VKTTN S L | VK7ZuX
21 VK7ZGG W f VKTXK l
28 | wnx 1w ! | vi7zRY
17,
ITEWS BROADCAST ROSTER ( CONTD,.).
Co~ordinators:
Horth-West: VK7AX Telephone: Work - 251044 Home - 252923
orths VKTKE " Hone ~ 312090
Souths VICTLW " Home -~ 285807
i7 A ATTR S
Emergency: Horth=est ~ VK7CF and VK7LH
llorth; - VKTPF, VK7RR, and VK7PD
Other Re-Broadcast Frequenciess
Horth-Wests 52.525 Mhz and 146 lthz R,
Horth; 7.130 kihz 1M
South: 146 hz and 435 Mhz M, 144.1 Mhz 231,
Qther Re-Broadcasting Stations:
Southern Branchs Peter VKTPS, John VKTZJG@, Mike VIKT7FB
North-test
Branch; Tony VK7AX, Terry VKITT, Tan VK7ZIE
g AA Ai o0 A e R S
Where substitutes are required for any of those listed above, it is
highly desirable thot this be arranged early cnough to give notice via
the previous
week'sbroadcast.
Hews Collection
Fither originating station or 80M re~broadcaster should check 3672 Khz
at 0915 hrs. local.
Notes
1. To facilitate the smooth running of the VK7 Broadcast the originating
station should come on broadcast frequencies at 0915 hrs. local to allow
re-broadcasting stations to set up equipment and test for system faults,
to ensure system is operational for the broadcast.
2. Originating stations using VKTWL/P are to keep a Log Sheet for the
Sunday morning News Broadcast. This Log Sheet is to be filled in each time
the station is originating the VK7 Divisional Breadcast and must also show
callback stations., This Log Sheet igs to be forwvarded to the Divisional
Secretary at the close of each Broadcast Roster period,