On 7/27/2021 12:53 PM, Morgan Bailey wrote:
80 to 100 dB band to band attenuation is necessary for a contest station.
That depends a LOT on the radios and the amps.
Reviewing Contest University the RA6LBS talk from a few years ago is the
basis for this decision. He probably has the most experience in this field
beside that of VA6AM. Both make great filters. Just having a filter is not
enough. One needs a multiplexer in conjunction with the band pass filter to
get to that DB level. One could stack 2 band pass filters and attain
whatever is needed to get the job done. The multi switchable boxes that run
about 500 to 900 dollars only give about 30 to maybe 40 db of rejection.
That also depends a LOT on the boxes, and some are far better than
others. See this study I did about 8 years ago for National Contest
Journal. http://k9yc.com/BandpassFilterSurvey.pdf Several of the units
are 10-20 dB better than that.
It
is just not enough to keep the other radio quiet and SAFE from front in
overload and toasting the receiver circuits. I use transmitting band pass
filters rated at 3500 watts on the output of my amp.
This is a very good way to do it. Most hams overlook the harmonics and
IMD generated in power amps.
This coupled with
multiplexers on 160/80/40 and 20/15/10 makes for a multi two or an SO2R
setup quiet on each radio. Between the multiplexer and associated band pass
filters I am able to run 1.5KW 160-10 with an antenna farm that takes up 68
linear feet total for 160-10. Additionally, 160/80/40 are vertical
polarized and 20/15/10 are horizontal polarized adding more rejection. It
works and works well.
One problem that many stations on a small lot have is ignoring Common Mode
pick up off the shield of the coax. Grounding all shields before entering
the shack
YES! AND seriously bonding everything in the shack and the building that
contains it.
and using 1:1 choke baluns is a necessary step to prevent
interstation interference.
Yes, it's quite important to have a SERIOUS common mode choke at the
feedpoint of EVERY antenna. http://k9yc.com/2018Cookbook.pdf
Having radios with very low composite/Phase noise is necessary.
YES!
At the last Visalia DX Convention, gave an overview talk on a dozen or
so mechanisms that contribute to inter-station interference, and how to
minimize each. It's here. http://k9yc.com/Multi-Station.pdf
And W2VJN's book on the subject is excellent.
73, Jim K9YC
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