Richard Fry wrote:
"Roy Lewallen" wrote:
All the power produced by the transmitter arrives at the antenna
less whatever is lost as heat in the transmission line.
_________

Roy,

If a transmitter produces r-f power, and a load connected to that
transmitter via a transmission line dissipates any of that r-f power, then
would you not agree that such an r-f transmission line conducts at least
whatever r-f power is dissipated by that load?

Of course.

And if such a transmission line can conduct power in one direction
(incident), it can also conduct power equally well in the opposite direction
(reflected), until the net result of incident + reflected causes line
failure.

No.

When the Zo of a transmission line matches the Zo of a load at its far end,
then that far-end Z absorbs nearly 100% of the power delivered there by that
transmission line.

This occurs whether or not there's an impedance match. If I connect my
transmitter to a 50 ohm dummy load via a half wavelength 300 ohm line,
all the transmitter's power (less the line loss) is conveyed via the
transmission line to the load. This is in spite of a 6:1 mismatch at the
load.

If those impedances are not matched, a reflection is generated that may lead
to the real-world, destructive and periodic effects on the transmission line
that I reported from personal experience, earlier in this thread.

In my example, as at any time the load and line aren't matched, there
will be standing waves of voltage and current on the line, which can
lead to line failure. In the example you gave, it was almost certainly
the high current points which caused it. If you'll pick up any
transmission line text, you'll be able to quickly see exactly what happened.

You still haven't explained how these imagined power waves cause
periodic effects. Please re-read my last posting -- is it some kind of
phase angle associated with the power waves, or is there some mechanism
by which they vary with position along the line? I'm looking forward to
your mathematical description of what you think is happening. You can
find mine in any textbook on transmission lines. If you'd like, I can
recommend a half dozen or more.

Roy Lewallen, W7EL