Message-ID: <24420.200101111304@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Thu, 11 Jan 2001 13:08:03 +0000
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Subject: LF: Rugby Loading Coils
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Reply-To: rsgb_lf_group@blacksheep.org
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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