In message <24420.200101111304@gemini>, James Moritz
<[email protected]> writes
Dear LF Group,
Alan makes reference to the loading coils at the 16kHz VLF station
at Rugby; A while ago I got hold of a couple of old papers detailing
the original construction of the VLF stations at Rugby (1925) and
Criggion (1943).
The loading coils for both stations were wound as spirals on five
hexagonal wooden spiders, roughly 4m diameter. The spiders could
be moved to vary the inductance, which was about 2.5mH for
Rugby, and 5.4mH for Criggion. The wood is described as
"American whitewood", which the Post Office engineers apparently
found was a highly satisfactory material; no other insulation for the
windings was used. The antenna voltage and current was 220kV,
400A at Criggion, and 160kV, 600A at Rugby. The windings were
(HF) litz wire made up from 6561 strands of 36swg. The Q was in
the range 2000 to 4000. The Rugby transmitter building was
designed to minimise the amount of metal, etc. close to the loading
coils, while at Criggion, the loading coil was inside a reinforced
concrete building. This caused high losses until a Faraday shield
was installed by lining the walls with a mesh of copper wires. The
Rugby transmitter building burned down in 1943, so we are not the
only ones with these problems!
Both these stations are still there (obviously modernised a bit), and
worth a look if you are passing by. Rugby is by the side of the A5,
and Criggion is on the Welsh borders a few miles east of
Welshpool. The road to Criggion village actually passes under the
VLF antenna, so you get a good view there.
It is also very interesting that the road under the aerials has been
covered by a form of Faraday shield held up by telegraph poles, distance
apart about 15 metres. They weren't there on my first visit but about
two years later, they were. I wonder why?
Mike
--
M.J.Powell
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