[TenTec] Power Power Power - revisited..

[Stuart Rohre]

Pete,  Most of your examples are from non RF cases of transistor stages.
Without going into the operating model of the transistor you assumed,
even with some current leakage in the "cut off" state, you would have to
agree, there is a tank circuit between the transistor and the line having
SWR. The Impedance of that tank, (parallel resonance) is non zero.  After
all, we are talking an anti resonance condition, where there is a mismatch
and therefore SWR.  At worst, the small current conduction of the transistor
should represent a high enough impedance, that the Standing Waves will
reflect at first encountering the tank circuit.

If the collector of the transistor has a high enough voltage rating, (well
above the operating voltages), it will even survive a residual voltage of a
High SWR condition with out the added back connected Zener diode that is
included in many single ended transistor output stages as a high voltage
protective device.  That is because little of the Standing voltage gets
beyond the tuned circuit if things are working correctly.  In "Reflections"
examples are given of space craft antennas (solid state circuitry) being
deliberately operated with SWR to accomplish other goals of the mission.

In any case, the papers in Communications Quarterly over recent years
acknowledge that SW reflection happens at the first tuned circuit before the
active device, whether tube or semiconductor.

There is debate only about whether the tube stage presents a conjugate
match, or what power state it is actually in.  The tuned circuits present a
match when finally adjusted to minimize SWR in the tuned circuit,
transmission line, antenna taken as  a whole system.