Ian White G/GM3SEK gm3sek at ifwtech.co.uk
Fri Nov 4 13:20:07 EST 2005

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 

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 

73 from Ian G/GM3SEK         'In Practice' columnist for RadCom (RSGB)

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