"rickman" wrote in message
...
On 10/6/2014 1:31 PM, Ralph Mowery wrote:
..

You are right, no even harmonics in a square wave. What circuit clips a
tone into a square wave just so it could be run through a low pass filter?


I thought we were going to start with a square wave. Nothing shapes the
square wave. You just run it through a low pass filter just above the
fundimental or 1st harmonic if you want to call it that..

The circuit I am thinking about is from an old RTTY audio tone generator I
built and was designed by Irv Hoff years ago, around 1970 or so.

He used a unijunction to generate a tone of 2125 or 2295 Hz (rtty tones)
then fed it into a 2 transistor multivibrator to generate good square waves.
Then into a low pass filter made of two coils and I think 2 or 3 capacitors.
This filtered out all the odd harmonics ( as there are no even harmonics in
the square wave) and just leaves the fundimental frequency as a pure sine
wave.

That way you could have a VFO going from 5 to 6 MHz and set the filter for
about 8 MHz and anything above that would be filtered out. No harmonics or
anything but a pure sine wave.

As I said, not sure if this would work at RF or not, just something to
think about.



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