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" <[email protected]>
To: <[email protected]>
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
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