Chris, G4AYT wrote:
> Very
> odd, when set up yesterday ae current was 600mA, today at start I
> could only get just over 400mA, then just after 1200 it had gone back
> up to 600mA. At both currents the SWR was OK.
I think you are experiencing voltage leakage (the equivalent of
adding resistance). An LF antenna has very high voltage on it,
especially if (as I suspect) your antenna is very short, even at
quite low power levels. This is much higher than the voltages you
will have experienced on 500kHz. This means that any leakage through
poor insulation, or even via adjacent damp walls or leafy trees, will
reduce your current. Even in a very well engineered system you will
notice a difference between summer and winter foliage (unless your
antenna is in the middle of a field), and current tends to peak when
it's freezing outside. Your antenna's environment is likely to to
have been wetter in the morning than later in the day.
What sort of insulators are you using? Does the antenna touch a wall,
plastic drainpipe or tree? A temptation is to use plastic string
(polyprop, washing line etc) as the sole insulation, or to regard
plastic guttering or a wooden window frame as an 'insulator'. At
higher power levels the error of this becomes obvious as you observe
the smoke, or your antenna mysteriously detatches itself from the
'string' and falls down.
Good luck!
Mike
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