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Cecil Moore[_2_] · September 4th 08, 12:51 PM posted to rec.radio.amateur.antenna

wrote:
Again, you seem to have the IEEE definitions of "differential"
and "common-mode" exactly reversed in your head.

Really? Do you believe the currents in a resonant 1/2 wave dipole are
common mode or differential mode?

Assume it is a 1/2WL wire in free space. Where
is the common reference?

I've heard antenna currents called "common-mode"
currents but neither Kraus nor Balanis call those
currents "common-mode". They are usually called
"antenna currents" (in phase, radiating) vs
"transmission line currents" (out of phase, non-
radiating).

In any case, differential currents on a transmission
line are 180 degrees out of phase and ideally, non-
radiating. Common-mode currents on a transmission
line are in phase and radiate. The currents in a
folded dipole are in phase and radiate.

Within a ferrite toroid wired in a 1:1 current-choke-
balun configuration, common-mode current induces flux
in the toroid with virtually none from differential mode.
If the device is made out of turns of coax, the differential
currents never see the choking impedance.
--
73, Cecil http://www.w5dxp.com