Message-ID: <001001c4cac1$40e588e0$6401a8c0@attbi.com>
From: "Jay Rusgrove" <JRusgrove@comcast.net>
To: rsgb_lf_group@blacksheep.org
References: <d6.19339725.2ec38c8d@aol.com><000f01c4c75e$a00d5ca0$bbab7ad5@jgtdiynm> <200411111539200989.0518CDF5@mail.zetnet.co.uk> <001401c4caa7$c59a7600$33d78351@jgtdiynm>
Date: Sun, 14 Nov 2004 22:14:43 -0500
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Subject: Re: LF: Loading coil
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Jim

Nice photo! You wouldn't happen to have a close up of the wood grain by
chance?

Two likely species of  American "white" hardwood would  be white oak and
white birch. Once kiln dried both maintain their dryness and
have excellent long-term dimensional stability. Have used both types
extensively in furniture making...can't say I've built any massive
loading coils, though. ;~)

Jay,  W1VD


----- Original Message ----- 
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, November 14, 2004 7:11 PM
Subject: Re: LF: Loading coil


> Dear LF Group,
>
> I have attached a picture of GBR's wooden loading coil taken last
year - the
> hexagonal spiders are about 5m across, the litz wire conductors are
about
> 50mm thick and I believe are 6561 strands of 36swg wire. The
inductance is
> of the order of a few  millihenrys. The papers describing the original
1926
> station indicate the coil Q was a few thousand; the timber used was
> "American Whitewood", whatever that may be - it was reckoned to be
much
> lower loss than other types of wood. The plates attached to the coil
frame
> said it was rated for 1000A at 16 - 22kHz.
>
> John Rabson wrote:
> > But didn't the helix house burn down once?
>
> I think that was in 1943, when the original wooden roof caught fire
and
> gutted the top part of the building containing the loading coil. The
lower
> floor housing the transmitter was repaired fairly quickly, but it was
not
> possible to replace the coil immediately, so a temporary outdoor
loading
> coil was used for a while. The coil in the photo seems almost
identical to
> pictures of the original 1926 loading coil, except that pairs of
spiders are
> paralleled up, presumably because the later antenna top loading had
more
> capacitance than the original, and required less inductance. Also in
1926
> the antenna feed was connected through a big glass window in the wall,
> wheras last year it passed through the (now concrete) roof. You can
see the
> copper sheet shield above the coil; also there was a grid of copper
wires
> covering the walls, which connected to the earth bus-bar, which can be
seen
> going round the wall.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>