On May 18, 12:33 am, K7ITM wrote:
I'm _still_ trying to figure out _why_ anyone would care about the
output impedance of a PA of the sort used at HF to drive antennas.
Nobody has ever convinced me that it matters at all, except perhaps as
academic interest.

Nobody is questioning the efficacy of design methods. Whatever works,
works. What we are discussing is indeed only of academic interest.
Knowing whether my IC-706 is conjugately matched or not does not
affect its operation at all.

From the time (t0) that a PA first outputs a Zg signal to the time
(t1) that the PA senses its load impedance is NOT zero time. How does
the PA know what its load impedance really is when it is not Zg?
Einstein's spooky action at a distance? No, feedback from the load.

Obviously, the PA receives some sort of feedback in real time. What is
the nature of that feedback? What can it be besides feedback energy
reflected from the load? (not in zero time, but at the speed of
light). In the real world, it takes measurable time for the forward
energy to reach the load and measurable time for the reflected
feedback (if any) to arrive back at the PA. The load seen at the PA
source is always an E/I ratio, i.e. a lossless image impedance that
always experiences a delay if it is not equal to Zg, i.e. it usually
contains reflected energy.
--
73, Cecil, w5dxp.com