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Old November 26th 05, 08:17 PM posted to rec.radio.amateur.antenna
Reg Edwards
 
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Default is voltage balun right choice?

Cec,

As an aside, there appears to be a little confusion about the various
uses of baluns which arises from their uncertain perhaps misleading
descriptions.

Because of the way balun winding-wires are run, they are often
described as transmission line transformers.

There are --

Voltage Baluns, Current Baluns and Choke baluns.

As I see it, Voltage Baluns have a definite voltage/impedance/turns
ratio and are true impedance transformers. They may be used as either
balanced-to-unbalanced windings, or be balanced-to-balanced, or be
unbalanced-to-unbalanced. Balanced windings may be centre-tapped.
One winding may be common to both primary and secondary windings.

Choke Baluns consist of a pair of wires wound together around a
ferrite core. The two wires may be of coaxial form or may consist of
a twisted pair or just a pair of wires laid alongside each other. The
two wires together form a transmission line of calculable impedance
and loss.

But a Choke Balun hss no impedance or voltage ratio. It is incorrect
to refer to it as having an impedance ratio such as 1-to-1.

A Choke Balun does indeed behave as an impedance transformer from one
end of its line to the other. But the transformation ratio is
indeterminate. The ratio depends on frequency and line length as with
any other transmission line.

The effects of inserting a Choke Balun between an unbalanced tuner and
a balanced transmission line to the antenna can be beneficial insofar
as tuner settings are concerned.

But in general, the length of line on a choke balun should not exceed
1/8th or 1/10th of a wavelength at the highest frequency of use. This
is not too difficult to achieve in the HF range of 1.8 or 3.5 to 30
MHz.

But I do not understand what is meant by a Current Balun.

Perhaps Roy, who is very good at it, could define what is a Current
Balun if there is such a thing. And while he is about it, Voltage and
Choke Baluns.

He may choose to give them different names. But his views can only be
beneficial to the mislading waffle which surounds them.
----
Reg.