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Cecil Moore[_2_] · September 3rd 08, 12:29 PM posted to rec.radio.amateur.antenna

wrote:
I disagree. There is no choking, there is merely a polarity and phase
shift between the "primary" and "secondary" of the 1:1 balun
"transformer".

In a w2du balun, zero flux in the beads is introduced
by the transmission line currents. All of the flux in
the beads is introduced by common-mode currents. Thus
the impedance of the beads *IS* a choking impedance
aimed only at the common-mode currents.

My choke-balun is ten turns of RG-400 on an FT-240-77
toroid. It's only purpose is to provide a choking
impedance to common-mode current. That choke-balun
doesn't know if it is being used as a UNUN or as a
BALUN.

Most baluns are designed such that near-zero flux
is introduced in the ferrite toroid by the differential
mode currents. Essentially, the only flux introduced
in the toroid is due to common-mode. The resulting
impedance *IS* a choking impedance.
--
73, Cecil http://www.w5dxp.com