I am looking for a balun (common mode current isolator) recommendation for
my receive loops, if I need a balun.
Because of my lot size I only have pennant and flag type antennas. I feed
them with a binocular core transformer per W8JI's and other's web sites
where the primary and secondary are two separate overlapping windings. For
my receive loops (3 fed from both directions in order to get two directions
out of each) I bring the RG6 feedlines away at right angles for 15', then
drop to the ground then they are underground till they get to a aluminum
panel on my shed. The receive lines from the antennas to the shed are
50-130' long. They terminate at a coax switch (I feed 12V through the coax
to switch directions on each pennant/flag) with a preamp on the aluminum
panel. The aluminum panel is tied into my common ground with the tower,
aluminum panel just inside the basement, AC mains box, etc. with lots of
ground rods (27), solid #4 copper wire and Cadwelds. The RG6 feedline runs
from the coax switch underground to the basement where it has a lightning
arrestor and a limiter. Then it runs up to the shack.
Should I add balun(s)? Where - at the antenna feedpoints, at the feedline
to the coax switch? Multiple places?
For receive lines what is the recommended balun? RG6 (how many turns)
through 2.4" (or smaller) #31 type material (how many cores?).
Tnx for feedback
N2TK, Tony
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Joe Subich, W4TV
Sent: Saturday, April 21, 2012 4:51 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Balun Recommendation
On 4/21/2012 4:26 PM, Gary Schafer wrote:
> Yes Ian, I agree with you that "common mode current" on a coax outer
> shield is a complete misnomer. It doesn't describe what it is "common
> to". If it were really common mode current it would have the same
> current on the inner conductors as well as on the outer conductor and
> be in phase.
While common mode current may be a bit of a misnomer, it is accurate in that
the effect of "outer shield current" is identical to that of common mode
current in a balanced system because of the "pin 1 problem"
that K9YC has written so extensively about. Since the signal return in most
amateur equipment is not tied to a complete and effective shielded
enclosure, the outer shield current is *indistinguishable* from a true
common mode current as it passes through the unbalanced input/output
circuits of modern equipment.
Again, if this "outer shield current" is sufficient it can appear in in
microphone inputs, be fed back into audio amplifiers or even be impressed
across control and power supply circuits. The results can be anything from
mildly annoying to fatal to the equipment depending on the level of the
common mode signal and the circuit involved.
73,
... Joe, W4TV
On 4/21/2012 4:26 PM, Gary Schafer wrote:
> Yes Ian, I agree with you that "common mode current" on a coax outer
> shield is a complete misnomer. It doesn't describe what it is "common to".
> If it were really common mode current it would have the same current
> on the inner conductors as well as on the outer conductor and be in phase.
>
> A better name for what is commonly called "common mode current" on the
> coax outer shield would probably be "outer shield current".
>
> 73
> Gary K4FMX
>
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