[CQ-Contest] SO2R Interstation Interference Issues

Jim Brown k9yc at audiosystemsgroup.com
Tue Sep 6 12:35:56 EDT 2016

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.


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.


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 

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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