Tom says:
>When strong CW signals are parked just outside the filter passband, I hear
>clicks that aren't as bad on the R4C. Anyone have any idea what could cause
>those clicks to be stronger? Something in the narrow filter?
Could be ringing in the narrow filter. Because the signal is outside the
passband, ringing generated by a transient in the first crystal could appear
as a narrow burst of energy - i.e. a click. Narrow filters really need to be
Gaussian response down to -6dB, and then revert to brick wall after that.
The previous owner of International Radio - not George Otsogeorge, W2VJN,
who has it now, he knows what he's talking about - tried telling me that it
was impossible for their filters to ring, but unfortunately, circuit theory
disputes that. Dave Leeson, W6NL, ex W6QHS, (the Leeson of Leeson's equation
for oscillator phase noise) told me that most narrow crystal filters will go
to a Gaussian shape on top if you badly mismatch them, but of course the
insertion loss goes to hell in handbasket.
You could experiment witha pulsed signal generator and mismatch the filter -
although the insertion loss would kill sensitivity, it might well show up
the clicks disappearing. Although most modern rigs seem awful on clicks to
me anyway.
73
Peter G3RZP
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|