I have been looking into gizmos that improve CW copy. Most are audio
tone detectors that ignore short impulse noise bursts and then
regenerate the CW with a keyed tone oscillator. There are several of
these designs around and they are all well and good, but I stumbled
across something different and was wondering if any of you have had
personal experience with it?

An October 1971 article in Ham Radio magazine (pg 17) titled
"high-performance CW processor for communications receivers",
"Frequency modulating the telegraphy signals in your receiver provides
an interesting and profitable addition to conventional receiver
design".

The idea is to sample the last IF of a receiver after as much IF
filtering as you can muster, and then using this as the RF input to a
FM modulator. The RF/IF is modulated at the audio frequency you like to
hear while copying CW. The next step is to frequency multiply the FM
modulated signal to increase the bandwidth and up the modulation index.
The following step is to treat it like any normal FM receiver IF and
run it through a limiter stripping off any amplitude information. The
last step is to put the signal into a normal FM discriminator to
recover the modulating tone you used.

What this is supposed to do is reduce or eliminate QRN (not QRM) from
the CW signal making a "quiet" background to copy the CW.

Have any of you ever done this and how did it work out for you?

- Jeff