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. That is, a 2 kW rated (at 1:1) balun is only good for 1 kW at 2:1
VSWR or 200 watts if your wattmeter shows a 10:1 VSWR looking at the
antenna. The reason is that the current (heating) losses in the windings go
up as the square of the maximum current - remember hearing about "I squared
R". A 4:1 VSWR means the current max value is twice the minimum, therefore
you'll be heating up the core four times as much as if you had a 1:! VSWR on
the line. It doesn't matter whether the line is unbalanced coaxial or
balanced open wire.


The other factor is core saturation.. flux goes as the voltage*frequency
.... so 10:1 VSWR means you might have 10x voltage..