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Dear LF Group,
Pleased to work Finbar GI4DPE and Pete M0FMT in my
first foray onto the 500kHz band just now. The QSB on Finbar's signal
was very fierce, going from 569 to inaudible and back over a minute or
so. It is quite surprising how good the signal strength is - then again,
the noise level is much lower than on 136kHz.
I had a few problems getting the system
working over the weekend - mostly to do with having nearly as much signal from
Radio 5 on 909kHz coming down the feeder into the TX as was going the other way
on 503kHz... it seems the combination of antenna tuner, coax feeder and TX
harmonic filter had an unwanted resonance close to the 909kHz TX
frequency, which is running 150kW about 500m away from me. Changing
the position of the low-pass filter to the tuner end of the feeder
seems to have solved the problem for now.
I am using a linear amplifier I built a while ago
for experimental purposes, turned down to about 4W output (it actually uses some
of the components, including the output MOSFETs, from my first LF TX
from 1999). The antenna tuner is similar to my LF set-up, with loading
coil, variometer and toroidal matching transformer, but with only around 300uH
total inductance. The antenna is the same wire I use for LF. For receive,
I am using the RA1792 with a loop antenna and preamp.
Cheers, Jim Moritz
73 de M0BMU
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