Thanks, Wayne. If not too much trouble that would be great. Or even a
run down of how you got the values. Maybe I'm just looking in the wrong
place. And I guess the ripple doesn't matter too much for a cw-only qrp
rig?
It would be very interesting to read a technical "why we changed this"
from rig to rig over time. But I guess that leads to problems with
tipping off the competition and being a bit of a time sink, too!
73,
Mike ab3ap
On 4/17/20 4:15 PM, Wayne Burdick wrote:
Hi Mike,
I can probably scrounge up the original Lm and other specs for you.
Varactor capacitance vs. voltage for the parts I used in the design is readily
available on the web. Just search for the part datasheet.
Varactor tuning of the filter is great for varying the bandwidth, but it is a
compromise in terms of loss and ripple.
73,
Wayne
N6KR
On Apr 17, 2020, at 12:55 PM, Mike Markowski <mike.ab...@gmail.com> wrote:
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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