[Elecraft] OT: Now Balun effectiveness

[Stuart Rohre]

What is a balun?  It is a transmission line and like all transmission lines
it has distributed inductance and capacitance.  However, it is so compact,
it emphasizes the inductance and capacitance and like lumped L and C tuned
circuits; then, it must have a finite bandwidth, although as Sevick has
shown they can cover most of the bands readily with high efficiency.  Use a
balun, that is fine, but remember there is no free lunch, and it is unlikely
to work 160 to 6m on one balun design.

Hams new to antennas and baluns worry too much about balun loss.   Try the
one in your tuner, transmit some typical QSOs, then take the lid off and
feel the balun with RF power removed.  Is it hot?  Then you have a concern.
Is it cold to room temperature?   Then it is doing its job without
complaint.

I am surprised that Lew first found that placing the balun at the input to a
transmatch was preferred over its placement at the output; but later backed
away from that.  The reason is that thinking about the impedance
environment, and thus the voltages the balun would experience, obviously in
the input 50 ohm environment, of transceiver to tuner, you have lower
voltages than the variable voltages and impedance extreme excursions at the
output of a transmatch as you go band to band with matching one antenna.
Perhaps, I am missing something else?

In any case, local experiments have shown satisfactory performance, (no
heating) of internal baluns of rugged tuners operated well within ratings.
However, it was shown that an external 4:1 Van Gorden balun tuned up with a
more readily found setting of the tuner for the same band, with same larger
than normal loop antenna.  Thus, there are balun differences everyone can
verify.   A larger balun  than the internal balun may be worthwhile to use
for peace of mind.

In buying used tuners, look inside and look at switch contacts for arcing
signs, and look at the balun for signs of heat.  Check that caps plates do
not rub and are equal spaced.  (However cap problems are easily fixed).
-Stuart
K5KVH