[CQ-Contest] Band pass filters for M/M

k8cc k8cc at mediaone.net
Sun Mar 12 21:45:31 EST 2000

Most of the commercially available band pass filters are not going to do you
any good between phone and CW in a single band because these are designed
for full band coverage.  Back in th early seventies, there was an article in
QST called "Field Day Filters".  These single band filters intended for your
exact application, and were hi-Q helical resonator designs which had to be
manually peaked at the frequency of interest within the band.  I can't
recall the issue or year, but I'll let your group do the research.

Another suggestion would be to use some attenuation in front of the
receiver.  On the bands you're interested in, 10 dB attenuation rarely drops
the signal enough to prevent a QSO.

Considering that you're running QRP, if attenuation does not help then
perhaps the transmitters are the culprit, generating low-level trash across
the band.  The Field Day Filters will help in this regard if in the
transmitter path too.  I can't recall the power rating of the original
design, but since you're running QRP I would not think this would be

Although you mentioned trying different radios, you might be looking in the
wrong direction.  Rather than looking for more expensive, modern radios, you
might want to look at older radios that don't use synthesizers.  General
wisdom is that most any Ten-Tec radio is pretty clean, or there are other
candidates.  The selection is somewhat narrow because you want all solid
state for DC power conservation and QRP adjustability, and many of the older
rigs like TS-830s are solid state except for the finals.



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