On Sun, 5 Sep 2004 10:44:04 -0500, "Richard Fry" wrote:

snip
When this test shows a 5% pulse return 2 µs after the incident pulse time
(for example), then the same pulse passed through the tx also shows nearly
exactly the same reflection % and time separation -- assuming there is
enough RF delay in the system for the reflection to be resolved in the
demodulated waveform.

As the directional coupler driving the normal demodulator at the TV station
is looking at forward power only, it is clear that the reflection from the
far end of the antenna system has been re-reflected from the TV tx output
stage, and NOT absorbed by it in its "conjugate impedance."

RF


Rich, I've got to tell you that you've just proved that the output circuitry of
the tx doesn't absorb the reflection from the antenna, but instead, re-reflects
it, because the output source resistance is not dissipative, only the cathode to
plate resistance is dissipative.

And the output source resistance is not dissipative or absorptive if the
impedance match is 'conjugate'. Contrary to what Mendenhall said that the tx
would absorb half the power if the source resistance is 50 ohms, there is
nothing special about the conjugate relationship that would produce this effect.
The tx will re-reflect whatever the match relationship is between the tx and its
load.

Walt