[CQ-Contest] dual bandpass filter experiment

[k6ll at juno.com]

I just ran a little experiment to see what additional
attenuation could be obtained from adding a second bandpass
filter in series with another one.

Transceiver 1 was transmitting about 2 watts into a
KLM Tribander.

Transceiver 2 was receiving on a Cushcraft tribander
about 40 feet from the KLM. In series with transceiver
2 were two Dunestar 6 band filter boxes, which have
an internal bypass position available.

Both transceivers were tuned to the same frequency, but
the filter boxes in series with the receiver were placed
on the "wrong" band. With both filters in line, the s-meter
reading was noted, then one filter was bypassed, then the
attenuators on the receiver were switched in to make the
s-meter come back to the original reading. There was about
18 inches of coax between the two filters.

Results:

tx 14 mhz, filters 21 mhz, 20 db additional attenuation
tx 14 mhz, filters 28 mhz, 22 db additional attenuation
tx 21 mhz, filters 14 mhz, 10 db additional attenuation
tx 21 mhz, filters 28 mhz, 20 db additional attenuation
tx 28 mhz, filters 14 mhz, 16 db additional attenuation
tx 28 mhz, filters 21 mhz, 14 db additional attenuation

The above measurements are pretty crude, but I guess they
are enough to debunk my 6 dB theory. I'll have to think
about that some more. If I have time tomorrow, I'll add
a stub at various places in the line to see what happens.

Maybe W2VJN or some other expert in the field will weigh
in on all this.

Dave Hachadorian, K6LL
Yuma, AZ
K6LL at juno.com


















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