Tom Rauch wrote:
>> Balun is really a misnomer
>
>Not really. Balance and UNbalanced in the context of antennas describes
>voltages, not currents. All two terminal feed systems, coaxial or
>parallel wires, have equal and opposite phase currents in each
>conductor when properly operating. The difference between balanced and
>unbalanced is in the voltages from each conductor to the environment
>around the conductor.
>
>Antennas that have less than perfect grounds have voltage from the
>shield terminal to "ground". That means they are not perfectly
>unbalanced. They are also not perfectly balanced. Most antennas are
>not perfectly balaunced or unbalanced, and we have no problem with
>using the term "balun" in those systems.
Sorry, Tom, I have a big problem about using the term "balun" around any
antenna that cannot ever be "balanced" as you define it - and isn't even
intended to be.
I agree completely with your definition of "balance" as requiring equal
voltages from each conductor to the environment around the conductor.
But that definition categorically excludes any vertical antenna close to
ground. Such antennas cannot ever be balanced voltage-wise, and they
aren't intended to be. There's nothing a "balun" can do for such an
antenna.
What all antennas do need is an assurance that the transmission line is
not accidentally becoming part of the radiating antenna system. When we
stop and think about it, that is almost always what we really mean by
"balanced". So why not say so?
>The correct term and device is actually a "current balun", because we
>want to be sure currents are balanced (equal and opposite) at the two
>antenna terminals.
I'd say the correct term is a "feedline choke" or "common-mode choke".
The device is exactly the same, of course. The difference is, now we're
saying what we really want it to do.
As I said earlier today, we hams have a remarkable talent for confusing
ourselves by deliberately calling things something different from what
they are. Please let's stop - the universe is already quite confusing
enough.
--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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