I clean up the sidetone on my Corsair II (when it bothers me) with an
external DSP filter. The raspy sidetone is a Tentec characteristic,
comes from using a relaxation oscillator that starts and stops quicker
(good for QSK at high speeds) than most sine wave oscillators. There's a
mod for one of the radios to rebuild the sidetone oscillator to give
more of a sine wave.
I'd think about making the sawtooth wave more triangular by inserting
series resistance in the capacitor discharge line of the relaxation
oscillator. A symmetrical triangular wave has only a few percent total
harmonic distortion.
A passive low pass filter in the speaker circuit can help clean up the
side tone and also high frequency noise from the IF and audio stages as
well as harmonic distortion. I've been able to create one with a
switchable cutoff using readily available parts. Its been published
locally, I believe I have it scanned also. Running 400 HZ CW tone with a
450 HZ low pass filter on the speaker to clean out all the receiver
artifacts is sure nice, nothing there but the CW.
73, Jerry, K0CQ
--
Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.
|