I bought 4 ICE 250W bandpass filters at WRTC and used them happily in a few m/s
operations. However, I was curious what was inside a box and to my great sur-
prise I found pair of parallel resonant circuits capacitively top coupled.
In the case of 20m filter, six 1000pF/500V mica caps were used, two in series
between the coax connectors and 1000+1000pF as parts of tuned circuits with
several turns of silver wire forming a selfstanding coils. Simulation of such
a configuration on ARRL Designer shows expected weakness in high frequency
attenuation as the whole configuration behaves like capacitive attenuator only
There was about 20dB attenuation all the way to TV bands so one can't get much
of TVI reduction. I guess, it would be too expensive to manufacture amateur
bandpass filters of DL7AV professional design published in CQ CONTEST magazine
I hope this doesn't sound too scientific for this reflector and on the contest
side call us in WAE RTTY this weekend and you will see 88 printed on your
screen from YL Jelka, S57NW! We will gladly accept 10 QTC or dump them to you!
73 de Mario, S56A, N1YU.
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