Rugby Loading Coils

[Andre' Kesteloot]

James Moritz wrote:

> 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 interesting to read the discussion at the end of the Rugby
> paper - some audience members state that the VLF station had
> effectively been rendered obsolete by the HF beam systems then
> coming into being - yet, 75 years later, GBR is still there on 16kHz,
> and it is the HF systems that have disappeared!
>
> Cheers, Jim Moritz
> 73 de M0BMU