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G3VGW > SWL 26.12.03 13:46l 156 Lines 8632 Bytes #999 (0) @ WW
BID : 10752_GB7NOT
Read: DB0FHN GUEST DK5RAS
Subj: BBC/Merlin Woofferton is 60
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<7M3TJZ<IK1ZNW<GB7CRV<GB7CIP<GB7COV<
GB7NOT
Sent: 031226/0950Z @:GB7NOT.#23.GBR.EU #:10752 [Arnold Nottingham] FBB7.00i
From: G3VGW@GB7NOT.#23.GBR.EU
To : SWL@WW
From: G3VGW @ GB7NOT.#23.GBR.EU 25 December 2003
Hello SWLs,
The BBC/Merlin HF station at Woofferton celebrated its 60th.
birthday in October this year, having been set up in 1943 using six
imported RCA 50 kW transmitters, although the ship carrying some of the
bits from the USA was torpedoed and they had to improvise to get two of
them working. The Engineer in Charge for many years was Laurie Ivin,
(G5IC) who used his amateur radio expertise to construct two working
transmitters out of the parts that had not gone to the bottom of the
Atlantic.
The transmitters as supplied by RCA used two triodes in push-pull
in the final. Senders 83 to 86 were complete, but Senders 81 and 82 were
a problem as vital parts were missing. One transmitter was built with a
"dummy" valve operating in push-pull with a real one! When I was
transferred there in 1963, Sender 81 still had a system of ropes and
pulleys to alter the PA coil coupling!
For much of its life, Woofferton was a Voice of America relay
station, being operated by the BBC on their behalf and earning valuable
dollars for Britain. The VoA programmes were received off-air at the now
defunct BBC receiving station at Tatsfield, Surrey and sent by landline to
Bush House, London and then up to Woofferton. The quality of the received
signal was often awful, so by the time it was re-transmitted by Woofferton
and landed in Eastern Europe it must have been dire! Latterly, high
quality satellite feeds were used.
Woofferton is situated right on the Shropshire/Herefordshire
border, the actual county boundary runs across the aerial field, which
must cause a few problems with charging rates on the place! Driving south
from Ludlow on the A49 you will soon spot the 250 foot aerial masts on the
right as you head for Leominster. The first BBC short wave station at
Daventry was built on a hill top site, as it was thought that hills would
give a better 'take-off' for signals but it was soon found that a flat
site was better, so that you could predict the angle at which signals were
sent, elative to the ground. Woofferton is actually in a valley,
surrounded by hills, but these are below the 7 degree minimum beam
elevation.
In 1962 the station was modernised and Senders 81 to 84 were
replaced by six Marconi BD272 250 kW transmitters. These are impressive
beasts, the pair of triodes in the final running 11 kV at 26 amps anode
current. Wavechanging was fun, you had less than 15 minutes to do it and
it involved manhandling very large and very hot coils and a lot of
knob-twiddling. Aerial switching was also manual.
Each array had 6 feeders going to it. If you can imagine that
most arrays have two separate curtains (called 'bays') connected together
by a 'bay' feeder. Half a wavelength behind the front curtain is an
identical one that acts as a reflector. If you feed the RF from the
sender to the centre of the bay feeder, then the beam will be at right
angles to the curtain.
(This is much easier to explain with a diagram!)
If you instead feed the RF at a different point on the bay feeder,
the beam will be offset to the left or right. You can therefore 'slew'
the beam by about 14 degrees either side of the natural bearing. So an
array intended for a bearing of 114 degrees (for the Middle East) can be
slewed to 100 or 128 degrees. Then of course if you feed energy to the
back curtain instead, the beam goes in the opposite direction, in this
case 294 degrees. (For the U.S. eastern seaboard) Plus you can slew it
to 280 or 308 degrees.
The man who was on aerial duties had to go out into the field, (on
a bicycle!) and at night all the light you had was a lamp on your hat.
Because of the way the schedule worked, quite a few arrays had to be
switched at around 03.00 GMT when we stopped transmitting to North America
and started to broadcast to the Middle East. Thus we needed to reverse
the beam from 294 to 114 degrees.
You waited by a telephone out in the field until you were informed
from the control room that the array was off power. Then you unhooked the
flexible piece of feeder at the gantry, using a pole with hooks at the end
and hooked it on to the feeder for the new bearing. You cannot leave the
other feeders simply disconnected as this would upset the array, so the
unused feeders have a short circuit placed across them. If you place a
short circuit on a feeder, then a quarter of a wavelength away it appears
as an open circuit, so is effectively invisible to the RF energy. This
wachieved by moving a 'shorting pole' around.
Doing this at night was quite tricky. To add to the problem, I
got quite nervous out there as with the wind making weird noises blowing
through the wires it was quite 'spooky' and to make it worse, sheep grazed
in the field and your lamp lit up their eyes!
Now, all this is done by remote controlled air operated switches.
This is a very good thing for the people at the Kranji station in
Singapore. When I visited there, they told me the hazard in the aerial
field is not sheep but snakes and crocodiles!
Being built in wartime, the station incorporated precautions
against enemy bombing. Each pair of senders was in a separate cubicle
surrounded by very thick walls. The roof was hinged so that if a bomb
fell in one cubicle, the roof would open and the blast would be dissipated
upwards, leaving neighbouring senders unharmed. This was the theory but
was never put to the test. However when the walls were due to be
demolished to make way for the new senders, the contractors had a terrible
job knocking them down!
The RCA Senders 85 and 86 survived for several more years. Anyone
familiar with the old HRO receiver would have felt at home, as they were
festooned with those wonderful HRO dials. The station has since been
modernised once more and now has the latest 300 kW transmitters which are
capable of remote control with no manual tuning required.
With the end of the Cold War, the VoA reduced its overseas
broadcasts and as the main function of Woofferton was to relay their
signals through heavy jamming into Eastern Europe, its VoA role has
considerably reduced and there was surplus capacity. This in part
prompted the decision to close the Daventry HF station and transfer its
BBC World Service transmissions to Woofferton.
I was lucky enough to get an invitation to the 60th. birthday
celebrations at Woofferton short wave site on the 17th. of October. You
will recall that it used to be a BBC facility before the HF sites were
sold off to Merlin Communications - a management buy-out. Since then
Vosper Thorneycroft have acquired the company. I went to the 50th.
birthday celebrations and really cannot believe that 10 years have passed
- I must be getting old!
When I worked there first, in 1963, the then new Marconi BD272 250
kW were just being installed. I was very surprised when I got there last
month to see that they are still there and going strong and still looking
very modern!
What has changed is that when I was first there, we had 9 people
on each shift. Now there are just two people on the night shift. The
Marconi units need a minimum of 15 minutes to change them on to another
band, as it involves changing several sets of heavy and hot coils. Thus
the Woofferton schedule is now designed so that where possible they are
operated on one band for long periods, with wave changes reduced to a
minimum.
As it turned out there WERE a lot of old faces there, including
one chap whom everyone thought had died! It was quite a gathering.
I have some scanned pictures of Woofferton - ancient and modern
if you are interested. Obviously I cannot send them by packet, but if you
have Internet access, send me your e-mail address and I will send them to
you.
--------
Season's Greetings and good listening!
73, Richard G3VGW @ GB7NOT (Ambergate, Derbyshire, UK)
(Edited & sent using a BBC Micro)
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