Bill,
what you describe points out again that it's important for developers to
look not just at the close-in IMD, but also at the wider spectrum. By
law all spurious output of a transmitter needs to be suppressed below a
certain level, and in practice a good transmitter suppresses such
products even more, so that under normal conditions they cannot be
detected over the air.
It's not clear to me how exactly that sizzling sounded and looked. But
there are several phenomena that can cause a transmitter to produce
spurious output at 10kHz from the main signal. Among them:
- Frequency synthesizer phase noise
- High order IMD
- Power supply noise
- Inadequate filtering after conversion from a very low IF
Any of these can happen due to bad design, or due to a failure.
I have heard many bad signals on the air. When I do, I usually report it
to the ham whose radio has a problem. Sometimes such a report is
welcome, but at other times it isn't. Some hams just don't like hearing
that their beloved radio is working poorly, and take such a report as a
personal attack!
Manfred
heard a great loud signal on 20 a few weeks ago,,,, crystal clear ...
but there was sizzling 10kc down the band....
the scope on the k3 showed it , did not appear big, but I could hear it..
moved to the 7800 and it was indeed there ,,,, still sizziling....
it was Italian ...I did not remember what power he was running,,,,
. maybe he was hitting it too hard???
maybe his amp needed another device to get into the linear region ???
I am no engineer... " but that's just wrong"
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