"Frank Gilliland" wrote in message
...
On Fri, 25 Mar 2005 23:15:46 -0500, "Leland C. Scott"
wrote in :

snip
For a filter, you can run both sides
of a stereo equalizer in series, and it can even tune different audio
freqs.

The stereo equalizer idea wouldn't work, bandwidth isn't narrow enough.
However a cheap DSP based single frequency audio band filter would do the
job. As cheap as these things, DSP chips, have become it shouldn't be a
big
deal.


Just for kicks I tried an old Rat Shack 10-channel (left and right
channels in series) while tuned to a CW pileup on 80m. Worked OK, you
could differentiate one tone from another, but it passed a lot of
noise. I also tried a 31-channel Sunn but the thing broke out into
oscillation...:-0 Maybe stereo equalizers aren't such a good idea.


After that, all you would need is a tone detector with a light
bulb. So the most expensive piece of equipment is already made and is
pretty common, while the other two pieces could be built from a kit by
just about anyone with a soldering iron.

The detector, indicator, device could be incorporated in to the DSP
filter
assembly.


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. 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.

Here's some interesting links you may like to look over.

http://web.telia.com/~u85920178/conv/syn-info.htm#intro
http://web.telia.com/~u85920178/right_01.htm


--
Leland C. Scott
KC8LDO

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