Herb Schoenbohm wrote:
> My question is why use baluns on low bands at all, especially on
> antennas like low dipoles or inverted vees, when feedline radiation
> probably does more for you in the DX department.
Feedline radiation is not the only problem caused by omitting baluns,
and it is not the most serious one. As you pointed out, it may
even be useful at times.
However, there are other problems which make baluns
(more precisely: common mode current supression) very desirable:
* preventing RF in shack, which may cause all sorts of
problems, especially with newer digital equipment;
* preventing losses on transmit due to energy being dissipated
instead of radiated (may range from a fraction of dB to ~10 dB);
* preventing noise (e.g. computer noise) going in reverse direction
and entering coax at far end, then goint directly to your
RX input;
* preserving resonance characteristics of the antenna (otherwise
the resonance you see may not be actual antenna resonance at all,
but a "parasitic" resonance of the entire "system" including
the outer surface of coax and whatever else that happens to
be connected; in extreme, but unpredictable cases this may
"pump" most of RF energy to shack/house/ground, not to antenna);
* preserving directional characteristics of antenna.
> There is however growing and persistent use of 4 to 1 baluns in almost
> every ATU on the market that offers a "balanced feed".
It works only with purely resistive loads.
With highly reactive loads, as typically presented by open-wire
lines, it dissipates most of RF energy. The user, mislead by
advertising, may still believe he has a "good match", at least
until the balun self-destructs.
> I did have a Johnson Viking KW Matchbox with the famous split
> stator breadslicers and no ferrite. In a moment of stupidity I sold it
> on e-Bay for $350.
In the moment of luck I bought one on e-Bay :-)
One of best investments I've ever made.
73,
Sinisa YT1NT, VA3TTN
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