Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.

Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

And also, what exactly do you mean by "balanced" in the context of a
feedline?

I agree that the effect is
the same, semantically, ie one side effect of the use of a balun is
less CM interference from coming down a balanced feedline but it is
there for a different reason.

Not in my station. My motivation for using common-mode chokes is
*specifically* to control any incoming and outgoing interference that
may be caused by common-mode currents on the feedline.

When the common-mode component of the feedline is reduced, it will also
be accompanied by an improvement in "balance" on the antenna, because
the two things go together (or at least, they do for some definitions of
that word). But "balance" is never my primary goal because I don't find
the concept helpful, either when deciding what to do next or when
evaluating the results.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek