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Old November 26th 05, 10:55 PM posted to rec.radio.amateur.antenna
Reg Edwards
 
Posts: n/a
Default is voltage balun right choice?

A choke (or current) balun is the correct choice.

The input impedance of the transmission line to the antenna varies all
over the shop from one band to another. So there is no definite
impedance to which the transmitter is to be matched.

A voltage balun is designed to match between two definite known
impedances of a given ratio, for example 4-to-1, 300-to-75 ohms,
values which never exist at your particular place in the system.

A choke or current balun is not intended to match one impedance to
another. It is intended only to allow, without loss, the transition
from a balanced line to an unbalanced tuner or transmitter.

Because the choke balun is in fact a short length of transmission line
wound on a ferrite core, an impedance transformation does occur
between one end and the other. But what the antenna line input
impedance is transformed to doesn't matter. It is just another
impedance for the tuner to handle and, as likely as not, the tuner
will handle it just as well. Just a change in L and C settings.
----
Reg, G4FGQ.