On Wed, 2009-02-11 at 18:27 -0600, Bob McGraw - K4TAX wrote:
> 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.
>
> 73
> Bob K4TAX
You have it all WRONG.
Go look at: http://bipt106.bi.ehu.es/psk31theory.html The envelope is
the characteristic of two tones spaced 31 Hz apart. That's the beat
note and the software makes the phase shifts when needed for keying at
the point in the beat note of zero power. Its NOT some AC power line
beat, which would be different in England with 50 Hz power than most of
the US with 60 Hz power.
73, Jerry, K0CQ
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