Hi Bernd, Ko and Uwe,
the annoying spurs centered on 137 kHz had reappeared in the morning of Dec
16th. They suddenly went away at 19:00 UT when power was switched down from
the daytime level of 500kW (i.e. both transmitters) to 250kW (single TX), but
were back in the next morning. After a telephone call on Dec. 17th, the
engineers in Donebach apparently were able to solve the problem. A few hours
later, the interference was completely cleared, and I have not heard it since.
The modulated noise bands in the spectrogram sent by Ko exactly look like
those I have seen here, though I was surprised about the strength at that
distance. What time did you take that image?
Uwe's observation on Dec. 22nd may be related to the familiar Luxembourg
effect, i.e. ionospheric heating impressing the programming of DLF (and
others) onto the carrier of DBF39. During many nights, the modulation depth
appears to reach a level of 1% to 4% here, equivalent to a sideband power of
a few watts.
Regards
de Markus, DF6NM
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