On Fri, 2006-12-29 at 15:05 -0800, Ron Castro wrote:
> The majority of IMD problems in PSK-31 are a result of trying to drive a
> microphone-level input on a transceiver with a speaker-level output from a
> computer sound card. That's about 40 dB too much audio, which will result
> in major IMD regardless of ALC action or output level setting.
>
> Since PSK-31 works by shifting phase, the amplitude variations caused by ALC
> shouldn't have any significant effect on either the IMD or readability of
> this signal.
Providing the ALC gain control introduces no phase shifts. With ears
being insensitive to absolute phase or even phase differences between
harmonic components, there is no need for a voice transmitter to hold
phase constant and there should be no expectation for phase to not
change with ALC changes of driver gain.
Yes, ears are sensitive to relative phase between them which is handy
for determining direction of a sound.
>
> Ron N6IE
> www.N6IE.com
> (Formerly N6AHA)
>
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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