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Daniele, the signal does not really look like
one of the RDL types, and I also don't think the "copies" are an aliasing
artifact. My guess would be a power converter running at 21 kHz,
modulated by 300 Hz from the ripple of a three-phase rectifier. The
frequency appears to be pulled every 0.7 s, perhaps by periodic load changes.
All just speculation of course...
Stefan's grabber has a bag full of 300 Hz
harmonics from a nearby tram, which is presumably running on raw
DC.
73, Markus (DF6NM)
Sent: Thursday, February 10, 2011 8:55 PM
Subject: LF: Intermod in the receiver - Advice
needed
Hello VLF,
I attach here a SpecLab screenshot where I have found that multiple copies of
the same signal are present. The signal at 21100 is probably genuine
RDL, while other copies at about +/- 300Hz look like intermod
products. However, I can't figure out the origin of this
300Hz "spacing", Any hypothesis?
Many thanks for your feedback.
Regards
D.
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