Hi Joe,
Are you running barefoot or using a power amp? Nearly all bandpass
filters are rated for 100-200W, so must be placed between the rig and
the power amp, so they have no effect on harmonics and trash produced by
the power amp. Stubs are the solution to power amp harmonics. Here's a
"how to" tutorial that I wrote for NCJ last summer.
http://k9yc.com/LocatingStubs.pdf
k9yc.com/7QP.pdf is a slide show that shows how well they can work. For
7QP, we had stations 80 and 40 with wire dipoles within 3 ft of each
other, and on 40 and 20 with antennas spaced about 10 ft, K3, KPA500,
and the stubs shown.
Of course, the radio that you use also matters. Some are much cleaner
than others. Here's a summary of ARRL Lab tests that I prepared several
years ago.
http://k9yc.com/TXNoise.pdf
Since then, ARRL Lab tests of the new Flex 6000-series rigs showed them
to be not very clean on CW. Not long after, Flex issued a firmware
update that I'm told made them a lot cleaner, but I can't get a Flex
user to loan me one to test and I haven't seen a re-test by ARRL Lab.
:) Soon after I published this review, Yaesu issued a firmware upgrade
that reduced the CW bandwidth of the FTDX5000. I did before and after
measurements of N6TA's radio, and the improvement was significant. I
suspect, but I'm not certain, that a similar upgrade applies to some
other Yaesu rigs of that generation.
W3LPL pointed out that harmonics and intermod can be generated in all
sorts of electronics and devices around your home. He mentioned rotators
as an example but there are others. Frank says this mechanism is usually
characterized by the harmonic being "growley" sounding. I've got a bit
of that here on a few antennas. No amount of filtering or stubs will
help -- we must kill this at the device where it is being generated. I
suspect that a good ferrite choke might help if the culprit could be
identified.
73, Jim K9YC
On Tue,9/6/2016 1:54 AM, Joe Galicic wrote:
I am in the process of building a SO2R station and have a question of
interstation interference and bandpass filters. I live on a very small lot and
have no room for antenna separation. I only have wire antennas and a vertical
for 20 meters. I have a set of bandpass filters for each radio. I still get
quite a bit of phase noise hash on adjacent bands even with filters. It doesn't
seem that the filters make any difference at all ? The biggest reduction in
noise is between the dipole antennas and the vertical. Can I ever expect to get
the noise to acceptable levels with antennas so close to each other ? Thanks
-Joe N3HEE
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