[CW] Learning hints

[Stan Barr]

D.J.J. Ring, Jr. wrote:
> Henry,
> 
> I remember such circuits - I wish I could find a schematic for one now.  
> 
> As I remember the explanation of the one that I used very many years 
> ago, the person had used a very highly selective audio filter - he used 
> one tuned to the tone of aircraft beacon Morse modulation - that fed a 
> circuit that keyed a nice tone.
> 
> The result on 80 meters during the summertime (when I used the unit) was 
> a nice clear tone with no background noise.
> 
> I didn't use it long enough to find out if it had any quirks that made 
> it undesirable - but I certainly was impressed at the way it transformed 
> a noisy band.

I built one some years ago using a NE567 phase-lock-loop chip driving
an af oscillator.
The main problem was false keying by noise spikes, but with a good 
pre-filter that wasn't too bad.