Date: Tue, 17 Apr 2012 12:27:49 -0700
From: Jim Brown <firstname.lastname@example.org>
Subject: Re: [TowerTalk] Balun Recommendation
Following up on Jim Thomson's love for strings of beads. It's quite
instructive to study the Fair-Rite data sheets for representative
parts. Go to the link below and enter the part numbers, then go to the
bottom of the sheet and study the impedance curves. Steve and I agree
that the curve for a string of single turn beads will be simply the
curve for one multiplied by the number of beads in the string.
## I’m not disagreeing with you at all.
Now, here's where we diverge a bit on our analysis of the usefulness of
strings of beads. Yes, a single turn through #31 (that is, simply
clamped onto the cable) shows resistance the same general order of
magnitude as reactance between 4 MHz and 20 MHz, you've got to have a
LOT of beads in that string to hit 5K ohms resistive, which is known to
be a good design value to make a dent in RX noise. By contrast, it's
easy to hit 5K with the multi-turn chokes on #31 or #43. The only times
I use a "string of beads" in single turn fashion are either at VHF, or
where it simply isn't possible to wind turns.
### yes, but can you hit 5K from 160-10m with a single balun design.
Sure, you can easily optimize for a single band, or maybe 2 bands.
Your typ balun manufacturer will want to build a balun that covers
all bands, so they end up with a compromise. Can you mount it
on a 3 inch diam boom, without adding a bunch of stray C.
Can you hang it in mid air, on your 80m dipole, up 100 feet, fed
with 213-U. To do this right, no one single design will work.
At a bare minimum, you really need one design for the lower bands,
and another for the higher bands. One for yagis and one for dipoles.
Likewise, the first place I saw any reference to the benefits of a
serious common mode choke to suppress RX noise was a publication by
W1HIS around 2006, and I immediately built some chokes, put them in
antennas here, and confirmed his assertion. He also said that 5K ohms
was a good design target.
A few years ago, some EEs working at CIA made contact with me, later
visited here for a brain pick. A year or so later, the leader of that
group sent me a DOD engineering report from the 70s that went down the
same trail I did, coming to nearly all of the same conclusions as I had
(and none in conflict), but missing dimensional resonance. They were
also designing to suppress RX noise, and came up with design target on
the order of 5,000 ohms and used multi-turn chokes to get there. That
report was probably never classified, it was simply a matter of lack of
communication between EEs working in different places.
73, Jim K9YC
### My understanding is the 5K MIGHT lower local noise only, like
within a 500-1000 foot radius. The 5K wont buy you anything for band noise.
Some folks see nothing, some see 1-2 S units with real high Z baluns
of your various designs.
## If the balun is mainly resistive, and you want it to handle high power,
and with high duty cycle modes like RTTY, AM, 10M FM, etc, and also
typ swr’s, then it will have to be high Z, as in several thousand ohms.
If it’s just 1-2 k ohm, and mainly resistive, it will overheat.
## I came up with a compromise, with type 43 bead baluns on all the
yagis....and a single type 31 UN-UN line isolator at the input of the
remote switch box at top of tower. The line isolator is just 4 x turns of
393 coax wound onto 4 x stacked FT-240 cores....and placed inside
a large nema box with 7-16 Dins on both sides. A 2nd line isolator
is in the basement. Between the type 43 bead balun and the line isolator
mounted to the mast on top of the tower, the combined Z is pretty high,
and nothing will overheat.
## I see on one of your dipoles, you have a 2nd identical balun, a few feet
below the 1st one. How close can you install 2 x identical baluns. I take
it the idea is to end up with a high Z by using 2 of em, nose to tail.
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