[Antennas] balun ratio question

[Robert Lay (W9DMK)]

It is a common misconception that a balun should be chosen on the basis of
the characteristic impedances of the two lines that it interconnects.

While that woul be true in the unique situation where the load side of that
system were a flat line, it is not true in any other situation.

In other words, in general, the balun has some completely unknown impedance,
anywhere from near zero to approaching infinity at its load terminals. Under
those circumstances you invariably have to do something to get the impedance
to a manageable level before you should even think about which is best, 1:1,
4:1 or 1:4, or something else.

I have been quite successful in using balanced L sections in my balanced
line which bring the impedance to a more reasonable value at the point where
the balun connects. Unfortunately, in order to properly design such L
sections, it is necessary to have measurements or good guesses of the
impedance at every band of operation. The calculations are not terribly
difficult but there are computer programs that I have available that make it
much easier.

If you don't do something to moderate that impedance seen by the balun, you
can pretty much kiss any hopes of getting a decent match at a decent
efficiency goodbye.

73 de W9DMK - Bob Lay, Dahlgren, VA
http://www.qsl.net/w9dmk
w9dmk at crosslink.net

73 de W9DMK - Bob Lay, Dahlgren, VA
http://www.qsl.net/w9dmk
w9dmk at crosslink.net