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Old March 13th 07, 07:48 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Jul 2006
Posts: 342
Default VSWR doesn't matter?

Richard Fry wrote:
"Roy Lewallen" wrote
The problem is that the idea of "reflected energy" turning the plates
hot is so easy to understand, that people aren't willing to abandon it
simply because it isn't true.

_____________

But reflected energy/power does exist.

For an easy example, such reflections are evident in the picture seen on
an analog TV receiver when the match between the transmit antenna and
the transmission connected to it is bad enough.

In analog TV transmit systems with a typical 500+ foot length
transmission line from the tx to the antenna, a 5% reflection from a
far-end mismatch can be quite visible, showing as a "ghost" image that
is offset from the main image as related to the round-trip propagation
time of the transmission line.

RF


Richard,

You are undoubtedly correct, but you have also demonstrated what is
really the lifeblood of many arguments in RRAA. You have introduced both
transient behavior and multi-frequency behavior.

Clearly these are important in the real world. However, the vast
majority of models and calculations used as support for RRAA postings
are steady-state and monochromatic. Anyone who stayed awake through
calculus and differential equations might recall that the equations for
steady-state and transient behavior are often quite different.

No one denies the existence of reflections. Some people get confused by
the mathematics of power and voltage. But a big argument is about the
round-trip travel of energy in the steady-state. Some people seem to
believe that energy continues to flow back and forth from one end of a
(mismatched) transmission line to the other under steady-state
conditions, even simultaneously traveling in both directions. (Passing
like ships in the night?) Since energy is a scalar quantity, and any
given joule is not distinguishable from another, it is not clear how the
proponents keep track of the bookkeeping, but they muddle through somehow.

73,
Gene
W4SZ
 
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