"Richard Clark" wrote
To date in this matter, I have yet to see any concrete value of source
Z offered from those of the NOT 50 Ohms camp. Further, I have yet to
see any of them offer any experimental confirmation of their assertion
Richard Fry wrote:
Below is a quote from a paper titled "A Study of RF Intermodulation
Between
FM Broadcast Transmitters Sharing Filterplexed or Co-located Antenna
Systems," by Geoffrey Mendenhall. (clip). Quoting Mendenhall, "...If the
source impedance were equal to the fifty ohm line impedance, half of the
transmitter's output power would be dissipated in its internal output
source
impedance..."
Walter Maxwell wrote
The last sentence in the paragraph above is incorrect. This shows that
the writer of the quote is in the unbelievably large group that still
believes
incorrectly that half of the tx power would be lost if if it were
conjugately
matched. But we all know that efficiencies greater than 80% is achieved
by Class C amps, and greater than 60% is achieved by Class B amps
when the source impedance of the tx is 50 ohms resistive and the load
impedance is also 50 ohms resistive.
_______________

To Walter Maxwell:

1. You may be interested in reading Mendenhall's complete paper, which I
will email to you. The lab measurements reported in it used two, operating,
high-power FM broadcast transmitters -- and support his statements about
amplifier source impedance and its consequences.

2. I will ask again, if transmitters have a 50 ohm source impedance, what
accounts for the fact that TV ghosts are produced by an antenna system
reflection having a sufficient delay time? Calculations and measured data
show that the energy that produced the ghost originated by re-reflection off
the TV transmitter output stage of far-end reflections in the antenna
system. If the tx source impedance was 50 ohms, it would absorb the far-end
reflection, which would be incapable of producing a ghost image.

Further, if the tx source impedance was 50 ohms, then the RF intermodulation
measured and reported in Mendenhall's paper -- and verified in real-world
installations by the radiated interference those IM products produced --
would not occur.

RF