The phase delay of a crystal filter changes rapidly at the knee. A
little frequency shift could easily be magnified by that phase shift to
sound like a wider chirp. It would seem to me to be best to make sure
the CW signal was inside the filter a ways to get away from that. Either
by selection of CW carrier frequency or filter frequency. Maybe it would
be better to introduce a totally separate CW crystal oscillator that
didn't need to go through the filter. I don't have any idea what that
would do to the switching, but ought to make it sound perfect. Though
its not easy to key a crystal oscillator without either clicks or
chirps. The crystal doesn't like stopping and starting... Probably
better to key a mixer to get a better on/off ratio that just keying a
straight gain stage with the oscillator running continouously.
73, Jerry, K0CQ
--
FAQ on WWW: http://www.contesting.com/tentecfaq.htm
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|