after following the discussion on Rugby's sidebands I had a look on the
spectrum as received here in northern Bavaria (JN59NK).
It seems that it consists of two transmissions in parallel: One FSK pair on
73164+-50Hz using 100 baud and the other on 73334+-50Hz with 50 baud. Both
have equal powers and are probably generated by a single tx! The problem
seems to be the intermodulation between the two: Here I could see 3 to 4 IM
products on each side of the carriers: IM3 is abt 24dB below each carrier,
IM5 29dB and IM7 33dB down.
I have included a small spectrogram display clearly showing the two signals
and their IM, using 43 Hz Bandwidth to time-resolve the fsk. In the averaged
line spectra (256 points beginning at 72 kHz and 2048 pts from 72.9kHz), you
can see that even here the IM dips into the noise (-66dB rx noise in 10.8Hz)
only at 72.0 kHz.
We have a somewhat similar problem in the Frankfurt region, with two
(seperate) transmitters in Mainflingen on 123kHz and 129kHz. Their IM3
product around 135kHz has sidebands up to 137kHz.
If you can hear one another in the IM sidebands within the UK and we can here
the noise down here, we should also be able to hear your transmissions (at
least in qrss or dfcw modes). So lets keep our ears open on 73.
73 de Markus, DF6NM
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