[TenTec] Built in SWR meter bannans

[Rick - DJ0IP / NJ0IP]

EXCELLENT!  Pretty convincing, Steve.

That explains the results I've seen on one of my recent antenna projects.
I have been trying to build an Ultra-Light OCFD for SOTA and have the
antenna doing what I want it to do, but with too much CMC.
This is not the same antenna you saw on my booth at the ham fest in Lincoln
last year, it is a different one.

I began by building it using a 2-core Guanella (my standard balun I normally
use), got the antenna working like I wanted, and then focused on reducing
weight as much as possible. I replaced the 2-core with a 1-core balun, which
cut the weight and wind load significantly. I have tried the 1-Core Guanella
and the New Improved Balun by N7ZWY
(http://home.earthlink.net/~christrask/Trask4to1Balun.pdf ) .  
Neither has brought the results I'm looking for.
I think you just nailed it.  Thanks.
Unfortunately you've led me to believe what I want to do, simply can't be
done.

While we are on this subject, Jim made a comment about not using twisted
pair in chokes, but it's ok in power transformers.
Is twisted pair an absolute No No, or only slightly worse?  Jim? Steve?
Anybody?

73
Rick, DJ0IP

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Steve Hunt
Sent: Wednesday, April 24, 2013 11:42 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Built in SWR meter bannans

If you wind a 4:1 Guanella balun as two identical 1:1 chokes on a common
core, you force the CM voltages across the two chokes to be the same because
they share the same flux. If we call the input voltage V, the balun then
drives the output terminals to +3V/2 and -V/2 with respect to ground. If you
had a perfectly balanced load that would force 3 times the current into one
leg compared to the other. Analysis here:

http://www.karinya.net/g3txq/temp/4%20to%201%20current%20balun.png

and here's the experimental demonstration on a 'scope using a perfectly
balanced 200 Ohm load:

http://www.karinya.net/g3txq/temp/bal1.jpg
http://www.karinya.net/g3txq/temp/bal2.jpg

Because of Sevick's pre-occupation with differential-mode performance he
never spotted that effect. In fact he made lots of DM measurements - DM
impedance, phase delays etc - but with a *floating* load; andas we all know,
if you have a floating load you don't need a balun to maintain current
balance :)

The simple fact is that a 4:1 Guanella balun wound as two 1:1 chokes on a
common core will force voltage and current *imbalance* with any non-floating
load; I don't call that "working" !

For a 4:1 Guanella balun to "work" properly and drive equal currents into
any load, the CM voltages of the two chokes must be able to take up
different values; they can't do that if they share the same magnetic
circuit.

73,
Steve G3TXQ


On 24/04/2013 21:30, Rick - DJ0IP / NJ0IP wrote:
> Steve, Sevick is right.  You "can" wind a 4:1 Guanella balun on a 
> single core.  I guess the question is, how well does it work?
> I have tried it both ways.  In fact I was using dual core's for a 
> couple of years until I read that there is very poor tolerance in the 
> cores... up to
> 20 % variance. Since I have no way to measure this and don't know 
> where to buy matched pairs, I begin to wonder how do I maintain 
> symmetry when there is 20% variance.  So I can't decide whether it's 
> better to use 1x FT-240 or 2x FT-140.  Any ideas on this?
>
> 73
> Rick, DJ0IP
>
>

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