Victor makes a good point here. One thing to examine and one point
often overlooked and largely not understood by hams and manufactures has
to do with baluns and common mode chokes. All are not created equal,
regardless of what the glossy advertising may say. Baluns in tuners
are largely incorrect designs and have been for years.
I recall that Jim, K9YC was asked to test a group of baluns of a certain
company, in preparation for use at an off-shore DX station. In summary,
his results indicated they were barely, if at all, a balun. Otherwise,
expensive junk!
Personally, I have all of Jim's works in a binder. I also subscribe to
the work of Tom, W8JI and that of Rick, DJ0IP. What they say and write
is fact! What is advertised is more "old ham lore" and they want you to
drink the "kool-aid".
What ever your choice of antenna and feed line orientation is your
choice. Likewise the correct balun and common mode choke. The latter
seems to create more incorrect information and results than favorable
ones. Follow the work of Jim, K9YC, Tom, W8JI and Rick, DJ0IP and
build your own. Do it correctly and they are easy and a whole lot less
expensive, saving one $100's of dollars and getting much better
results. If there was a good commercial balun available, I'd recommend
it. But....sorry to say.....I haven't found one.
73
Bob, K4TAX
Message: 6
Date: Fri, 26 Nov 2021 10:10:36 +0200
From: Victor Rosenthal 4X6GP<k2vco....@gmail.com>
To:elecraft@mailman.qth.net
Subject: Re: [Elecraft] Background Noise with Mike Plugged in to Rear,
, Mike Jack
Message-ID:<dcc00a52-7050-ba7d-5540-ab59da4c3...@gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
In my experience, the single most important factor in reducing RFI
problems is to prevent RF from flowing back into the station via common
mode current on the feedline. This is easiest to do with balanced
antennas. If they are coax-fed, then you need the appropriate choke at
the feedpoint. And if the coax does not run perpendicular to the
antenna, then a choke will probably be required at the entry to the
shack as well.
Balanced antennas fed with balanced line like window line or open wire
line work best with true balanced antenna tuners. The common practice of
feeding a balanced line running a high SWR via an unbalanced tuner and a
balun is less efficient both from the standpoint of power loss (the
balun gets hot) and choking efficiency (the common mode current gets
through).
An inherently unbalanced antenna, like an OCF dipole, also requires
choking, but the demands on the choke(s) are higher.
RFI problems will vary according to the lengths of the feedlines and the
band in use. A system that is clean on one band may be dirty on others
if common mode currents aren't suppressed.
The time to apply ferrites is AFTER you have done the best possible job
of reducing common mode currents, and after all your equipment is bonded
together. I found that bonding my metal operating desk to the system helped.
73,
Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
https://www.qsl.net/k2vco/
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