Manfred, thanks very much for your reply defining "end-to-end" and the reasoning for 170VRMS.
After I'd read it I still didn't understand why the voltage across the CMC end-to-end was half the transmitter voltage, and a simple example that I'd come up with (in which I reduced the feedline length to 0 and replaced 1) the antenna with a floating load resistor and 2) the CMC with a perfect transformer) resulted in the CMC end-to-end voltage being unknown. In other words, the loop equation for the this very simple circuit reduced to Vload = Vsource with Vcmc cancelled out.
Clearly I was missing something, and the answer was in your reply to Dave in which you said that there would be no end-to-end voltage across the CMC if the CMC "has one end connected to a floating load without any coupling anywhere else".
Ah ha! That was my error -- my load was floating. If I instead split the load into two series-connected resistors (each with half the value of the original load, i.e. a center-tapped load) and added a resistance from the load's "center-tap" to ground (i.e. a common-mode path), then the load's center-tapped is forced to be 0 volts.
(The CMC, in this case, being an ideal transformer, forces the currents to be equal and thus no current "bleeds off" through the common-mode resistor. And with no current through this Common-mode resistor there is no voltage drop across it, and thus, because one end of this path is grounded (0 volts), the other end at the load's center-tap must therefore also be 0 volts. And the voltage across each of the CMC's windings will then be equal to half the load voltage by virtue of the load's center-tap being 0 volts and the fact that Vsource = Vload.
Interestingly, it seems that if the common-mode path is unbalanced with respect to the load (i.e. the load is not tapped at its center, but off-center), the voltage across the CMC will be less than half the source voltage -- so a "balanced" load would seem to present the worst-case voltage across the CMC.
Anyway, lots of assumptions in my "ideal" model (e.g. CMC = ideal transformer), so there could easily be a flaw in my reasoning. Please let me know if I've missed something.
Thanks,
- Jeff, k6jca
