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Message-ID: <b0FUXCA7ghX6Ew4y@pickmere.demon.co.uk>
Date: Thu, 11 Jan 2001 20:31:55 +0000
To: rsgb_lf_group@blacksheep.org
From: "M.J.Powell" <mike@pickmere.demon.co.uk>
Subject: Re: LF: Rugby Loading Coils
References: <24420.200101111304@gemini>
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In message <24420.200101111304@gemini>, James Moritz
<j.r.moritz@herts.ac.uk> 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