Post below

REALITY CHECK: If tx source Z really was 50 ohms, a tx connected to a 50
ohm load would lose 1/2 of the RF power it generates to that internal Z.
And if that is true, then the heat produced by the tx, and the AC power
consumed by the tx would be proof of that.

However careful measurement of heat production and AC power consumption of
broadcast txs (for example) does NOT support the belief that the source Z of
a tx designed for 50 ohm loads IS 50 ohms.

Following is the output of an old DOS program I wrote years ago to show
operating parameters for a 25kW FM broadcast tx manufactured by my employer,
when operating at any RF power and line voltage in its rated range. These
values closely track the average of factory test data accumulated over 100s
of delivered units.

In this example, if the tx had a 50 ohm source Z it would have to generate
50kW of RF in order to deliver 25kW to a 50 ohm load. In the first place,
it doesn't have a big enough power supply or a big enough PA to do that.
But even if it could, the input power and heat production would be almost
twice the real values shown below.

The same physics applies to ham transmitters, which should be verifiable by
an unbiased evaluation of comparable operating parameters.

- RF

* FM TRANSMITTER AC LOAD *

Transmitter name (HT-??FM): ? 25
TPO in kW: ? 25
AC line voltage: ? 220

RESULT:

Total Tx = 103.7 amps/phase, 39.5 kVA total.
H.V. Power Supply Current = 92.7 amps/phase
Total AC/RF Efficiency = 66.5 %

PA Air = 400 cu. feet/min.
Tx Cabinet Flushing Air = 335 cu. feet/min.
Power Supply Air = 250 cu. feet/min.
Total Air = 985 cu. feet/min.

Total Heat = 42810 BTU/Hr.
Heat Rise, total tx system = 39 deg. F.
Air Conditioner Load = 3.6 tons

____________

"Richard Clark"
"What is the source Z if it is not 50 Ohms?"
(clippage)
The answer is the transmitter source Z is 50 Ohms at rated power.