"Owen Duffy" wrote
This second point of reflection could be a transmission line
discontinuity, but it is most likely that it was that the tx end of the
transmission line was not matched, that is that the tranmitter did not
terminate the line with a near perfect match.

It leaves the questions "are transmitters matched to Zo in real life, is
matching an unavoidable consequence of optimising power output?"
___________

Field experience in my tenure with RCA Broadcast when measuring and
minimizing the "ghosting" propensities of commercial analog broadcast TV
transmission systems showed/shows that a measured 5% or greater voltage
reflection from the transmit antenna/input elbow complex, when sufficiently
displaced in time from the main image, will result in an objectionable ghost
image seen on an off-air TV set tuned to that station.

That would not be true if such a nominal 5% far-end reflection from the
antenna system essentially was absorbed by the TV transmitter (whether or
not that turned the tube PA plates red, or caused the failure or other
compromise of a solid-state PA).

Maximizing the output power and efficiency of a broadcast r-f amplifier
dictates that its effective output Z must be greatly different than the load
Z it is expected to drive. In the case of broadcast transmitters, that
source impedance is low (a few ohms), compared to the typical 50 or 75 ohm
Zo of the load it is driving.

And this it the reason that much of the voltage reflected from an
antenna/far-end mismatch returns from the tx back to the antenna to be
radiated, and so to produce the TV ghost image seen under those conditions.

An equivalent effect is a reality in FM broadcasting, where a poor Z match
of the antenna system across the FM channel bandwidth produces synchronous
AM, and adds to stereo and SCA crosstalk.

RF