Nicolae Santean wrote:

So really, the question stands up. Please be more elementary in explanation.
Thanks a lot.

An electrical generator is most efficient when the load impedance(1)
is the same as the generator impedance. That is when it can deliver
the most power.

In a receiver setup, the antenna is the generator(2) and the leadin
cable + radio is the load. When the two impedances are matched, as
above, the maximum amount of energy can be transfered from the
antenna to the radio.

The leadin coax + radio has a set impedance, as does the antenna(3).
The 'balun' or 'unun' is the means used to match these two items via
a ratio of windings.

Sometimes the balun is used directly between a tuner circuit and
antenna..usually in a transmitter setup. The rules for receiving and
transmitting antennas are very very similar but as a rough rule of
thumb, receiving antennas are more forgiving of design errors.

Lots of good sites out there. a quick search will get you some more
results.

http://www.qsl.net/aa5tb/balun.html
http://home.att.net/~DickWD8CEB/Balun.html


(1) Impedance is opposition to current flow, not necessarily of the
resistive kind only.
(2) A wire being crossed by radio waves generates a small electrical
signal.
(3) A normal, fixed length of wire as opposed to the multi tapped
varieties used by those with large antenna farms..


mike




mike