"flipper" wrote in message
news
On Tue, 26 Jun 2012 22:09:21 +1000, "Alex Pogossov"
wrote:
As far as the parasitic FM is concerned, do two simple experiments.
1. On a quality comms receiver in SSB mode listen to the carrier (set beat
frequency to a few hundred hertz) of your transmitter.
Without applying any audio, halve the cathode resistor of 6ME8 (touch it
with another resistor in parallel), effectively simulating +100%
modulation
excursion. Ideally, pitch of the beat tone shall not change. If it
changes... you have FM.
2. On a quality comms receiver in SSB mode listen to the carrier (set beat
frequency to a few hundred hertz) of your transmitter.
Without applying any audio, play with the antenna tuning capacitor of your
transmitter. Ideally, pitch shall not change, only the volume as you tune
to
and detune from the resonance peak. If it changes...
If you do these tests, could you "report" the results here. Then we can
discuss what causes FM in each of these cases.
I don't have a SSB receiver.
Oops, surely you are not an RF guy.
Then do another trick instead.
Tune any AM radio into a strong local AM station within tuning range of your
transmitter. Then tune your transmitter to a close frequency so that you
hear beat frequency on the radio. It is better to have the signal from the
transmitter stronger than this station so that you do not hear the audio but
only the beat whining (with some sideband chatter of course). Then proceed
with the above described tests. (A carrier of an AM station is even more
stable than any communications receiver.)
Regards,
Alex