On Tue, 22 Sep 2009 09:52:46 -0700, Jim Lux
wrote:

The other factor is core saturation..

Hi Jim,

The only reason why a common mode choke (a more appropriate BalUn
construction for any application) would encounter "core saturation" is
due to the presence of a very significant common mode current - the
thing the choke (or BalUn) is supposed to suppress. If the "core
saturates" this is an indication that a common mode choke is very,
very necessary.

The better the choke (the higher its common mode Z), the more it will
snub the current. The more it snubs the current, the less chance of
"core saturation."

The solution to a hot BalUn is suppression of the current that is
energizing the "core."

As for:
Karl Beckman wrote:
First thing to remember is a really radical thought: The power rating of a
voltage balun has to be decreased by the highest SWR factor existing on the
line.

I have NEVER heard this apocryphal "rule of thumb" before. For one
thing, it doesn't make sense on the face of it as it defines a linear
relationship between current (or voltage) with power.

73's
Richard Clark, KB7QHC