"Hans" ) writes:
Hi,

since a view days I own an TTrx350D, second hand. I notice an annoying
beep / hetrodyne in the background when I'm listening to amplitude
modulated stations in ssb mode: AMU-AML and ECSS.
Strange but SAM sounds ok=E9! When I'm listening to hams everything is
also ok.

So, there is always a hetrodyne tone when I'm listening that way. Very
annoying!!
Is there someone else how recognise this problem and knows how to cure
it?

Assuming you are treating the AM signal as an SSB signal (ie using
an SSB filter and the product detector for demodulation), the beat
is hardly unexpected. The AM signal has a carrier, and then you've
got a "locally generated carrier" in the receiver.

The point of tuning the AM signal as SSB is that the narrower filter
knocks out the unwanted sideband, and attenuates the carrier of the incoming
signal enough that it is too weak to cause a noticeable beat against
the receiver's BFO.

But if things aren't tuned properly (be it the BFO in the receiver
isn't adjusted properly, or the main tuning isn't adjusted properly)
then there will be a beat note, and that's expected.

The whole point of synchronous detectors is to take this a step
further, keeping with the advantages of beating a locally generated
signal against the incoming signal. But the actual bit that synchronizes
things ensures that the locally generated "carrier" is right where the
incoming signal's carrier is, and then there can never be a beat between
the two.



Michael