Naw, its too rough for a square wave, its a saw tooth from a relaxation
oscillator. I cleaned one of those up once by putting a resistor on the
discharge side to make an equal sloped triangular wave, less distortion
(8% total harmonic distortion) than a square wave. Used it for several
years for running RTTY by feeding audio to a SSB transmitter. I don't
remember the details now, but it would involve probably adding one
resistor to the Corsair II sidetone oscillator. I think I had pots for
dual rate charge and one for single rate discharge and adjusted the
interacting pots for the two tones I desired to create with minimum
distortion as seen on the oscilloscope.
I've not worried about my Corsair II that much, the tone doesn't upset
me, why its cleaner than the buzzers we tried for code practice
oscillators back about 1953!
There have been discussions on this topic that should be archived here
or at tentec@qth.net.
I keep an DSP audio filter connected to my Corsair, when its set for SSB
2 Khz bandpass mode, it cleans up the side tone beautifully. I've seen a
mod suggested to add an op amp low pass filter to the radio, or to
replace the present oscillator with a phase shift oscillator that has
inherently sinewave. The trouble is that the phase shift oscillator and
low pass filter prevent the sidetone keeping up with truly high speed
keying (somewhere above 40 wpm) and the lengthened sidetone will hang
over into the receive time when running QSK. Alternative oscillators are
hard to key without click or chirp too.
I sometimes use a passive audio low pass filter on the speaker wires of
my radios, that cures the distortion of the sidetone, too.
73, Jerry, K0CQ
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