[Antennas] 4:1 or 1:4?

[George, W5YR]

"Steve L." wrote:
> 
> These comments are making me scratch my head, since I
> designed and wound Kevin's balun:
> 
> > I would get rid of the 4:1 balun first thing, Kevin.
> > It is only making bad
> > conditions worse.
> 
> > the end of the line due to a high impedance there.
> > Your 4:1 balun is just
> > making the problem 4 times worse than a 1:1 balun.
> 
> This is a 4:1 step DOWN balun. It takes the high-Z
> he's seeing and steps it down 4:1, not UP. The only
> problem you'll see is with certain very low-Z inputs
> where the 4:1 is definitely not appropriate.

Depends, of course, on how it is hooked up - original poster didn't say.
> 
> I use four of them in my high-power setup without the
> slightest problem, but I DID have to trim the balanced
> feedlines to get that 'sweet spot' where no crazy-Z
> was presented to the balun's input of course. No balun
> will operate way outside it's transmission line would
> impedance, unless it's a very low-mu material that
> isn't working very well to begin with.

And this is the crux of the problem and the solution. The balun loses its
4:1 or 1:4 properties when dealing with out-of-range impedances. A balun is
NOT a transformer and cannot be treated as such. What it actually does in
the world of impedance transformation depends directly upon frequency and
termination impedance, as well as physical and electrical construction.

The "best" way around this situation in a practical sense it to avoid any
need for impedance transformation in the balun itself and rely upon it
solely to make the unbalanced-tp-balanced connection conversion. The 1:1
toriod and bead baluns are essentially frequency and load impedance
independent and they "do their thing" regardless of how they are being
operated.

That is why I recommended using one.
> 
> If you want to use the very best balun setup, isolate
> your entire transmatch using a non-conductive chassis
> and use a 1:1 50Ohm ferrite core current balun on the
> transmitter side of the transmatch. This works great
> except no commercial matcher does this, you must build
> it from scratch yourself and it doesn't work well with
> really high-Z loads since there is no impedance
> transformation at the balanced side. The balun always
> sees it's characteristic impedance on both sides (when
> you have the transmatch tuned, of course) so it's
> happy at all times and you can use a higher mu ferrite
> without worries.

Well, this has been debated and written upon many times and the answer
always comes out the same: there is no practical advantage over placing the
balun on the output of the tuner and using a 1:1 choke device for the
conversion. While the input location of the balun may assist it in seeing
its design impedance, placing it there does nothing to enhance the balance
of the feedline system. In fact, under certain circumstances, it makes the
unbalance worse. 

The fact that you find no such commercial products pretty well tells the
tale about this configuration. I have used it and found no merit to it at
all,  having to isolate the tuner cabiner and putting up with hand capacity
when making adjustments.

Theory and commercial practice have demonstrated over time that the simple
C-L-C T-tuner will match a wider range of loads over a wider frequency
range with less loss and at lower cost than any other configuration. Place
a 1:1 choke balun on the coax output to transition to a balanced line and
there you are.

Bottom line: use baluns or ununs to make connection conversions and to keep
common-mode currents from the outer braid of coax feedlines. Use tuners,
transformers, and other impedance-matching devices to effect impedance
matching.

72/73, George W5YR - the Yellow Rose of Texas   QRP-L 1373 NETXQRP 6       
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe SOC 262 COG 8  
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437

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