Denny wrote:
There
are no waves of average power bouncing back and forth on a
transmission
line.
************************************************* ********
You really mean that Roy, or am I misreading?
I agree that no 'average' value of power is reflecting, but with a
mismatch at the antenna terminals, voltage/current is definitely
sloshing back and forth on the line making standing waves at .25L
intervals that we can physically probe and measure...

Waves of voltage, yes [1].

Waves of current, yes [1].

Waves of average power, no.

History repeats itself in this discussion, so someone is sure to come up
with that snappy line about: "Feel the dummy load on the reflected power
port of a broadcast TX! If there's no such thing as reflected power, how
come that load gets hot?"

That's sloppy thinking. You are not looking directly at the main
transmission line - you're looking at the output of a directional
coupler that has been inserted into that line. Without the coupler,
there's nowhere to connect that load.

That coupler is a transducer. It samples signals from the main line, and
then it does things to them.

A directional coupler does NOT sample waves of power from the main line.
It samples the voltage and current on the main line, adds the reflected
components in phase, and delivers them to the output port labeled
'Reflected'. Connect a dummy load there, and sure enough it will get
hot... but that's only through the action of the coupler.

The challenge is still on the mat from several previous rounds: can
anyone provide a fully detailed description of the operation of a
directional coupler, circulator or similar device, based ONLY on waves
of forward and reflected power? It can be done easily using forward and
reflected waves of voltage and/or current, but that approach is
off-limits for this challenge. Believers in waves of power shouldn't
need it.



[1] Real hams can blow their own holes in the side of the coax - we
don't need no broadcast TX :-)


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek