Richard Fry wrote:

There is a general belief that a balun should be used where coax
connects to the feedpoint of a 1/2-wave dipole (for example), to avoid
RF current on the outer surface of the coax outer conductor -- which can
affect antenna input match, radiation pattern etc.

But does even a perfect balun fully remove these effects?

There are two sources for common-mode current. One is
conduction. The other is induction. Since common-mode
currents are somewhat unpredictable, the best way to
ascertain if there is a problem is to measure the
current. A toroidal pickup slipped over the coax will
give one a relative reading and is super simple to
implement.
--
73, Cecil http://www.qsl.net/w5dxp


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