On Mon, 28 Jul 2008 10:18:31 -0400, Harold Mandel wrote:
>A balun will generate heat.
Yes, but how much heat depends on the design and quality of
the balun -- the number of turns, the core material -- and
the operating frequency (again, the core material).
>Manufacturers of popular baluns realized
>stations would attempt to load RF into
>huge mismatches and because they wanted
>to reduce warranty claims, went for the
>cheapest solution that would withstand
>heated wires the longest.
The use of coax rated for high temperatures was part of the
original work published on common mode chokes (current
baluns) published by W1JR and W2DU. Further, it has been
shown (by W8JI, among others) that mismatch is NOT a
contributor to heating in a choke balun. Heating in a
current balun is proportional to the square of the common
mode current. An effective common mode choke (current balun)
will add a very high resistive impedance in series with that
common mode circuit, reducing that current to a small value,
and making dissipation small.
73,
Jim Brown K9YC
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