Bob - I think your thought about 2nd harmonic may be a very significant
factor. I know that in my original Orion 565 I was trying to do a AF freq
response watching the RF amplitiude on a meter - Things looked screwy at low
frequencies up to about 100 cycles -Then I hooked up my scope and looked at
the RF envelope and there I could see the generation of very significant 2nd
harmonic with AF input freqs under 100 cycles . Above 100 cycles that went
away. I did not try to figure out where it was coming from as I was not
really interested in USING the Orion with AF inputs under 100 cycles -it
just showed up in testing . I have not looked at my OII to see if it does
the same .
The ne thing that went thru my mind is that the ESB guys should love that -
it was a trick the old AM radio designers used to use to make the bass sound
better .
73 de Hank K7HP
> In thinking about this a bit more, if the slow sine modulation is seen
> while
> using the PSK mode then I would suspect the 2nd harmonic, being 62 Hz, of
> the PSK signal beating against the 60 Hz line freq producing a 2 Hz
> difference and modulating the PSK signal. Now the real question, if
> indeed
> it is the 2nd harmonic of the 31 Hz PSK signal, then where is it being
> generated?
>
> Typically 2nd harmonics come from a single ended stage that is incorrectly
> biased or is being over driven. Sound card, interface box, input stage to
> the radio are all suspect and good places to start looking.
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