Hi Alex,
Am 13.09.2011 20:47, schrieb Alex K:
Hello Markus, Stefan, LF!
My receiver is on my workplace, therefore at night I can't supervise its work
directly. On screenshots I have noticed that with approximately 17:30 till 02:55 UTC quality
of reception strongly worsens.
This is probably just the opening band (DX) with its propagated QRN and
stronger levels of BCD stations that may cause some IM in your preamp or RX?
At first I thought that it, possibly joins any powerful device and creates a local QRN. To learn that
this such, I have added in sheduled actions wave.record. In the morning, having come for work, I have
analysed this record. It has appeared that the entrance signal from the aerial increases at night almost in
10 times. The microphonic amplifier of my sound card strongly there were nonlinear distortions. I have
switched off the microphonic amplifier and have reduced factor of strengthening of the receiver
(receiver has no AGC); probably, it will allow to have pure reception at night time.
So a continuous line on 136172 Hz is result of nonlinear distortions in the
microphonic amplifier.
What is your RX antenna, an E field probe, right?
You could run a wideband window (0...24 kHz or so) and check when and
where the overload occurs, if it is within the displayed band at all. If
the S/N in permits, you may lower the microphone gain or the preamp
gain. Otherwise a band filter should help. This does not need to have a
very high Q, depending on what makes the overload. 10 dB reduction
reduces the phantom traces by much more than 10 dB, if it is IM.
PS On screenshots each division of a scale of amplitudes is 10 dB
OH! 10 dB ? I thought 5 dB. Then this reception must have been very well
;-) But the QSB is interesting too.
73, Stefan/DK7FC
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