"Tam/WB2TT" wrote in message
...

"Richard Fry" wrote in message
.........................
...............................
Concept below

However this is not an accurate model of a transmitter.

For an example, take an old Heathkit DX-100 generating a measured 180
watts
of CW RF into a matched 50 ohm load. To do this, it does NOT also
dissipate
180 watts of RF into some "virtual" internal RF load in the DX-100. In
fact, the PAs and power supply in the DX-100 could not produce a total
RF
output power of 360 watts without exceeding their ratings.

The dissipation in the PA is essentially related only the DC to RF
conversion efficiency of the PA, which in this case probably is about
75%,
max (Class C). So a PA input power of about 240 watts DC is required to
produce 180 watts of RF output power. The other 60 watts of plate input
power is converted to heat by the PA tube anodes.

The entire RF output generated by the PA stage is applied virtually 100%
to
the output connector. How much of that is absorbed by the load
connected
there is a function of load SWR and system losses.

- RF
There is a Motorola ap note that agrees with what Richard is saying. To
paraphrase it, if the the DX100 had an output impedance of 50 Ohms, then
the
overall efficiency would be 37.5%.

Unfortunately I can't read all the digressions in the thread. I skim by
author...

This is an interesting twist, Tam. I think if this were the case, then
there would be MORE power dissipated in the Tx than Mr. Fry is saying -
making the situation worse. By that, I mean, getting further from what is
going on. I think this goes in the wrong direction. I believe the flaw is
believing that the Rs=RL must exist for the transmitter.
--
Steve N, K,9;d, c. i My email has no u's.