Dear Stefan, Paul, LF Group,
I would agree that something like DFCW100 or DFCW200 with about 0.1Hz shift
would be a good candidate mode for further DX tests. DFCW is about 2 -3
times quicker than QRSS, also because there are two frequencies, there is a
better chance of seeing at least one frequency if narrow band interference
is present on the other. I have just tried setting Spectrum Lab to directly
generate 8970Hz DFCW200 audio output from the sound card and it seems to
work OK, so generating the signal should be simple, although for /P use, you
may need a bigger external battery to power a laptop for long enough to
actually transmit your callsign!
I am not too suprised I did not see DK7FC's signal yesterday - I had left
my receiver set up for QRSS30 reception, not knowing what transmission mode
would be in use. So several dB SNR would have been lost by not using the
correct FFT parameters. Also, Paul's 5mHz FFT resolution was longer than
optimum for QRSS120 reception.
I left the spectrogram running overnight and through today - see the
attachment for about 14 hours duration this morning/afternoon between 8900 -
9100 Hz. Sorry about the image quality, but it gives the general idea.
Ignoring the narrow-band QRM, the background noise is several dB lower
during the early part of the day, and several dB higher at night, than
during yesterday's tests. So the morning would be a good time for tests, it
seems. The jagged lines are the 179th and 181st harmonics of the mains
frequency - sometimes these also drift onto 8970Hz. The pattern of more
stable lines also sometimes causes QRM on 8970Hz. I don't know what these
are - the pattern of lines suggests they are harmonics of a fundamental
"carrier" of about 31.5Hz, with "modulation" around 5 - 6 Hz. They are
present continuously during most of the day, but overnight appear with 50%
duty cycle, switching on and off once every hour. Any ideas?
So at my end there is potentially substantial improvements in reception to
be obtained by using the correct FFT parameters, and also by using a /P
location with lower noise levels. I will certainly be interested to take
part in the next test.
Cheers, Jim Moritz
73 de M0BMU
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