AR Sept 76 VK7RR Sth Repeater
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DREAM OR NIGHTMARE:
A REPEATER FOR SOUTHERN TASMANIA
B. J. Morgan, LL.B. VK7AR- {
42 Avondale Grove, Mount Nelson |
Hobart, the capital city of Tasmania, a solid state repeater. Enthusiasm was not dusty and abandoned but still in one. ¥
nestles snugly beneath the high and an air of gloom and dismay per- piece.
4,000-odd foot Mt. Wellington. vaded the project. The receiver was un- Some two years after first ascending the
Since the earliest days of amateur stable, the exciter was too broad, the mountain, the repeater was brought back
radio, Hobartians have tooked fondly final was temperamental and ig make mat- to sea level having had less than one
at that mighty magnificence and ters worse two members of the committee hour’s use. The first step was to build 2
swooned at the thought of a VHF were newly married! The operation was teliable keyer. This presented no prob.
site to end ail sites. Thus as again at a standstill but this did not deter Jem to one of our engineer amateurs
equipment became more and more the old eyes from still casting covetous VK7AW, who in a short space of time
portable, mountain topping DX- glances at the mountain top from time
had a very satisfactory little man working
peditions became regular events to time. away on MCW from inside a small di
and results invariably justified the Towards the end of 1975 it was realised cast box. The repeater was plugged in: |
trouble. that a local amateur who also was an and turned on. Nothing. In case the
Then one day a new word came into the employee of Telecom, was the engineer shock had been too much the process: was
language — Repeater. Those eyes which responsible for antennae and cables etc. repeated with the same result. A careful:
were growing dim fram many years of on the National TV tower on the moun- inspection of the innards revealed that
covetous glances at the mountain top, tain. Thus the question was cautiously the transmitter was OK but the receiver
began to dream of a repeater io per- born, "What about moving the vaive re- was the perfect attenuator. Not having
petuate their dreams and ambitions. 1970 peater”. But where was it? After much any need for such a good attenuator,
came and construction of a repeater was careful looking, a piece of coaxial cable was pulled out and work commenced:on
commenced. The initial work was carried was found protruding from a dark corner fixing it. Hours and hours later, after:
out by Ron VK7ZRO and Dave VK7MD. By and at the other end was the device, very countless cups of black coffee it again:
the middle of 1970 a repeater was in
existence except for a bug free keyer,
antennae and a site. The equipment was
comprised of a 1674 transmitter exciter
board into a low power final delivering 25
watts of power; the receiver a modified
Ranger 800 2 with 6CW4 front end. As a
unit this repeater was used on a manned
basis for a short while, but increasing
commitments necessitated a change in re-
peater committee.
The ‘Northerners' by this time {to the
uninitiated, the northern branch of the
Division) had been causing strange splut-
ters to appear ‘a bit above channel A”
and suddenly there was a licensed re-
peater in Tasmania and the Southerners
had been beaten to the punch. However,
Not to be outdone, the Southern repeater
under a new committee, finally managed
to ascend the mountain two years later.
Antennae were erected on the commercial
television tower and initial tests were com-
menced. However, afl was not as it
should be. Spies in the north of the State
were sent out to give signal reports. Com-
parisons between the repeater and a
mobile some 100’ below showed a notable
difference — the mobile could be heard
the repeater could not!
Faced with this result, the committee
Carefully stored the repeater in a corner
of the building and repaired to warmer
climes. it was obvious that a rethink was
necessary. Was the lo-loss cable not so
lo? Was the transmit power too low? Were
the antennae unsuitable? Time passed
and the repeater was forgotten until one
day came news of a fire on the moun-
tain. The damage was not severe but a
decree was issued by the owners of the
building that no valve equipment was to
henceforth be stored therein. The re-
peater story that had never started, had
just ended.
Another committee was formed to build Inspecting the aerials of VK7RHT. Photos: B. J. Morgan and W. T. Moffat VK77™
level for the week whilst we were waiting
for the new cable. Some of the lightest
Moments in the saga came whilst users
{not knowing that we were not using the
proper antennas) sat in the city, gazed up
at the tower and expressed all sorts of
theories about why signals were noisy even
where they could see the tower. It was
fortunate that the inventor of co-axial
verticals did not have to endure the
criticisms of angle of radiation, etc., whilst
the unenlightened discussed the faults
of the antenna at jength. Returning to the
now completed cable run, the truth about
the aerials was revealed and the two tower
antennae were connected, the power output
was increased to its nominal 75 watts and
the big switch was turned on. We then sat
waiting for reports. We were not long in
waiting. In the first few hours, reports
came in from over 100 miles away, from
a hand held unit some 60 miles away and
from mobiles 50-70 miles away. As a start
then the repeater was working and very
weil at that.
Aiter two weeks of air testing the equip-
ment is still being run by virtue of an
operating permit to enabie interference
problems, etc., to be dealt with, if and
when they appear. To date there has been
nothing untoward occur. We have been
advised that channel Two (new band plan)
has been confirmed as our operating
channel and the call sign VK?7RHT will
soon be granted.
This story in reading does not ade-
quately relate the problems experienced in
Final tweak before going into service. setting up a repeater on a “congested”
mountain top. Whilst we did not need io
emitted noise. But what sensitivity? When swapping cabjes from antenna to antenna purchase or erect towers, eic., we had to
cold it was giving 20 dB quieting at 1 the fault was traced to one of the cables. counter any possible intermodulation faults
microvolt, as it warmed up this decreased Next job — fix the cable. caused with commercial services in the
fo a miserable 5 microvolts. Saturday, May 8th was C day. Bright vicinity, ensure minimum cable loss (the
The repeater was set up for evatuating and early at 6.45 a.m. Brian and Tom met run te each antenna is a minimum of 350
performance, for a 1 month test period and started off for the mountain top, it.), engage the voluntary services of quali-
itom a 1000’ elevation, at an amateur’s Andrew and Phil followed. The weather fied and medically suitable riggers to carry
fesidence. This gave time for considera- was against us and it was impossible to do out the installation and connection of the
tion of antennae at the new site and a any work. It was agreed that, subject to antennas and cables and perhaps most of
modern receiver. The month passed and the weather improving, the repairs would all, to work in sub-zero temperatures
unfortunately we were no further ad- be started the next day. However, whilst amidst ice and snow, gale force winds and
vanced, A rebuild of the transmitter final the weather was satisfactory, we had for- driving rain, all taking their turn to hinder
had been considered desirable and at the gotten Mother's Day and so the work was the workers.
same time the power output was raised to called off again. Sequel. The repeater has already shown
18 watts. An STC 131 receiver was can- During the following week, with the itself to be the realisation of a life’s dream
Sidered a very good basis for a new re- assistance of some amateurs who were for those intrepid pioneers of the mountain-
eater receiver and at no cost one was also authorised tower climbers, one top gazing. Perhaps not surprisingly it has
obtained and modifications carried out. Ht antenna was raised to the 232 ft. platform attracted many old timers to 2 metres. The
Was heartening when, after many long and a cable run was taken up from the success of the project already can be
and sleepless nights spent huddled over 90 ft. level to the top antenna. It was gauged when, in a conversation recently,
benches and FET’s, the receiver was giving realised that time was working against us two OTs new aspirants to 2 metres were
20 dB of quieting at 0.35 microvolts. because of the risk of deteriorating both trying out their multi-channel mobiles.
Maybe the repeater might work well after weather. Several weeks were spent in trac- One suggested they go to 3,590 and the
all The committee at this stage consisted ing out the faulty cable and trying to repair reply was, “Which channel is that on this
of four. Phil VK7SS was responsible for it. Ultimately it was discovered that the tig?”
antennae. Andrew VK7AW for the keyer cable was completely full of water and Equipment TX : TCA 1674 + QQE06/40
and timing circuitry, Tom VK7TM and was beyond repair, After much discussion final, 75 watts out —
Brian VK7RR for the transmitter and re- and a meetitng of interested parties, it was
agreed to purchase new lo-loss cable at a Receiver: STC 131 modified frent end with
ceiver,
price of approximately $300.00. On the MPF 1000 and helical resonators.
Then came the big test. Towards the
end of Apri! antennae were erected under 29th of May this cable was run in the most Cable: Andrews FHJ114 foam filled, HM9
‘he go" platform of the onal TV tower. g and rapidly jorating weather air pressurised,
There were two existing runs of fo-loss conditions. However, everything was com- Antennae: Home built, stainless steel co-
table that were surplus to requirements pleted and then came the big moment. axial verticais, sealed in potyurethane
aid these were obtained on loan. When But to digress for a moment, Brian and compound and fibreglass.
Connected it was obvious that either one Tom had decided to run the repeater trans- Timer and Keyer: Home-brew using iCs.
table or one antenna was faulty. By mitter on a temporary aerial at ground Ez