On Sat, 26 Mar 2005 11:40:53 -0500, "Leland C. Scott"
wrote in :

snip
Come to think about it, how about just a 567 or 4046? Either chip
would probably do it as long as the radio doesn't drift too much. And
if I'm not mistaken, both have a VFO on the chip. So a CW 'adapter'
could be a single-chip project -- no DSP required.

Those two chips are just simple PLL building blocks. There isn't a way to do
any tone filtering as such unless you make the VFO frequency range vary
narrow which would have the same effect.


That's the idea.


The 4046 has a range and frequency
offset capability using just two resistors and a capacitor. You would want
to use the phase-frequency detector, not the simple XOR phase detector which
could lock on harmonics of the audio tone. That would be the chip to use.
The lock detect circuit could then be used as the visual signal device for
CW. Something this simple you could breadboard in an evening to see how it
works.


Actually, it only took about 15 minutes, but it doesn't work. Capture
and release times are too erratic within the bandwidth, and any other
CW signals within about half an octave make the thing go spastic. It
-might- work if the loop filter Q could swing with the VCO freq, but
that ain't gonna happen with just a couple chips.

Setting a narrow capture bandwidth, and using the clarifier (or BFO)
for tuning, works pretty well. I also tried a state-variable with a
schmitt trigger. Discrimination was better; but high Q, cumulative
drift and fading made it difficult to get a clear copy.

I should add that it's been quite interesting trying to read Morse
with an LED..... after a few minutes it's almost hypnotic. I tried
different colors, and while a big green LED was the best it was still
irritating after about 10 minutes.







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