I haven't yet successfully decoded anything with Opera on 136khz in
spite of seeing some very big, clear signals on the waterfall display.
HF results are very satisfactory, especially on 30m. This problem
applies using any PC or laptop on the premises.
The Rx is the Kenwood R5000 which produces some images below Long Wave
but sensitivity is quite good. I use a 136kHz bandpass filter with a
-60dB notch at 200kHz and better than -40dB for all frequencies above
that. The Rx filter is normally set to 2.1kHz USB and there is a useful
notch filter.
There is a choice of antenna and preamps. One antenna is effectively a
sloper, 10M of open-wire feeder at 45 degrees connected to a horizontal
delta loop of about 140M total length. This can be used with the Tx
loading coil to tune, or a tuned preamp with about 20dB boost at 136khz.
The other is a 1m square of 10mm copper tube, broadly tuned into an
in-built +10dB preamp which will take about 200mVp-pk input before
clipping. The earth/ground system is extensive.
Naturally an alternative receiver would be good but I have nothing
available, the FT817 and FT897 seem quite deaf at LF. Any suggestions
would be welcome,
Hugh, M0DSZ.
PS: I will probably be on 136khz this weekend with about 200W dc into a
linear amplifier but will note listening activity in case it's all
elsewhere.
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