In message <65AECDF1F89AD411900400508BFC869F0D7509@pdw-mail-
1.dera.gov.uk>, Talbot Andrew <[email protected]> writes
I have been told that the current loading coil at Rugby now consists of
an assembly made up of 50mm diameter copper pipe with a slider to permit
rapid tuning changes. The coil is about 3m high and a quick calculation
means that for 2.5mH (the antennas probably haven't changed much since
those days) there will be something like 40 turns and be 3.7m length -
which sounds about right based on hearsay. I'm trying to negotiate a
trip there with the group who remotely monitor that transmission as a
health check, but need a valid enough sounding reason to get past the
gatehouse. It will have to be on a Tuesday of course, wouldn't like to
be near that shed when the Tx is running !
Studying the layout of the masts on a map (a 2km long site with the wire
in a figure of 8 pattern, plus multiple vertical feeds, say 8km in
total) then do a quick calculation of wire capacitance based on 5pF/m,
the capacitance comes out in the region of 40nF - which just happens to
be the value to resonate with 2.5mH at 16kHz. Nice to see the rule of
thumb calculations working out for big systems like this :-)
People who are interested in these old transmitters may be interested in
the site of the old Caernarfon transmitter, built 1913, demolished 1938.
(Brilliant thinking). The concrete foundations for the masts are still
there, the field is littered with pieces of shattered insulators (like
our old 'egg' insulators but about brown and 12 inches long when
complete. Best of all is the building, still standing virtually complete
and now used as a riding school. If you inspect it (with permission) you
can still see the old feed-throughs, and match the patterns of the
brickwork with the old photographs.
It ought to be made a listed building. There is no other of that period
still standing, and if they can list a WW II radar mast then this is
even more historical. 1915 - 100 wpm to New York 24/7 and not a valve in
sight! First pictures to Australia too.
Sorry for lecture - my favourite subject!
Mike
G3IJE
--
M.J.Powell
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