[TowerTalk] Ladderline - what are the facts??/

[Ward Silver]

> Recall that common mode chokes work by adding a high resistive impedance in 
> series with the common mode circuit.

Recall also that the common-mode circuit for coaxial line is on a separate conductor from those carrying the differential-mode signal, creating a "three-wire" system in which the common-mode currents are flowing on the outside of the coax shield, completely independently of the differential-mode currents flowing on the inside of the shield and the outer surface of the center conductor.  That means remedies for the common-mode signal can be applied to the "third wire" without affecting the differential-mode signal.

For parallel-conductor transmission line, though, there is no "third wire" - the common-mode signal flows equally on both wires of the line, along with the differential-mode signal.  Anything that affects the common-mode signal is going to have an effect on the differential-mode signal, as well.

73, Ward N0AX