For fun, I thought I'd make an archeological dig and take a look at how
things changed from NorCal 40a to K1 since they're easy to study. Then
I realized part of it is not so easy for me. The 40a uses a Cohn filter
and I thought I'd run through analysis (not simulation) of it. Again,
just for the exercise of it while cooped up during these viral
stay-at-home days.
However, the data sheets I downloaded for the HC-49 crystal don't seem
to have the motional capacitance and inductance. So, two questions
arise: (1) I thought these were provided by crystal makers, the experts.
Are they expected to be measured or is there some simplification in
network analysis that doesn't require them?, and (2) are there Cohn
filter tables like there are for Butterworth and Chebyshev? I can't
find anything on analysis after a fair bit of googling.
Moving on to the K1, receive filter bandwidth is controlled by changing
capacitance via varactor diode voltage. But that comes from the DAC and
requires probing to determine voltage that in turn sets capacitance for
the filter. I can't find much on varactor controlled Cohn filters. So
(3), is there a place to read up more on it?
Tnx es 73!
Mike ab3ap, suffering cabin fever
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