Hi all,
things seem to have been pretty quiet on the reflector this week, which has
given me the chance to go "back to basics". (Didn't some daft political
party witter on about that and get roundly trounced a couple of elections
ago?) Never mind, the case of the disappearing antenna current has been the
subject of much agonising and brain-bashing this week and I am happy to say
that some of the anomalies have been found to be more apparent than real.
Having got Madame out of the way for a guzzle, gurgle and gossip session
with one of her pals I obtained unrestricted access to the microwave oven
and conducted a number of tests on the materials used in my various
erections (if you'll pardon the expression).
The conclusions are that the lighter and cheaper the plywood, the greater
the losses. Samples of the good quality material used for the endplates and
ribs of the big coil barely warmed at 850W, as did the hardwood dowel. But
the cheap, thin plywood used for the 'dogbox' got fairly hot by the time the
coffee water boiled.
However, allowing for the differences in frequency, power levels and spacing
involved, only a small proportion of the vanishing amps could be accounted
for by this alone.
Cutting a long and exasperating story short, once the test gear had been
checked out and found wanting in certain respects (I had completely
forgotten that it had been built and calibrated for 73 KHz using toroids of
dubious origin and was more than a bit out at 136KHz); a number of
alterations made to the 'angle of dangle' of the vertical wires and their
attack angle to the coil; a reworking of the antenna current sensor
placement; and the discovery of a puzzling anomaly - still to be resolved -
in the earthing arrangements, it would appear that now 205W at 73KHz and
100W at 136KHz each put about 75% more current into the antenna.
Neither the position of the coil relative to cement block and/or brick walls
better than 1/2 coil diameter away, or its height (checked at intervals up
to
better than coil length) above a concrete path made seemed to make any
appreciable difference.
This is a very worthwhile improvement and encourages me to continue with T/A
beaconing
on 136KHz, but only more or better reports and QSOs will show whether the
increase is more real than apparent.
Volunteers for skeds on both bands would be welcome.
The only thing I can say for certain out of all this is that coffee is
better for cerebration than Merlot, but for relaxation it's the other way
round!
73 de,
Ian GI8AYZ/MI0AYZ
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