Well, the reflected power is created by a "virtual transmitter" at the
feedpoint of the antenna and heads down the coax which has a surge
impedance of Z0 ohms. It meets the SO-239 at the TX and sees an
impedance of Z1, the impedance presented by the PA and output filters.
If Z1=Z0, the power is dissipated as heat in the PA and associated RF
circuitry. If Z1<>Z0, some is dissipated and some is reflected, where
some is radiated, and some is reflected [virtual transmitter again]. Ad
infinitum, and when forever is over, it is all gone and everyone lives
happily ever after.
SWR and all the associated measuring equipment and concern with it only
became an issue when: 1) Coax replaced parallel lines and; 2) Resonant
output circuits were replaced by solid state amplifiers with
non-resonant filters. When I sat for the Extra in early 1956, the only
question that involved standing waves was one about how Lecher Lines
could be used to measure transmitter frequency.
It's important today but calculating it hasn't changed. At 10 W, a 2:1
SWR will probably work ok. At 1500 W, a solid state amplifier may not
be happy with the voltages developed at its output connector.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 4/9/2019 5:56 PM, Don Sanders wrote:
Since no one has answered your question. I will venture a
supposition that many know but few will speak out.
And some still remember their CB days and the erroneous
advertising saying the power is lost.
Reflected Power flows back down the feed line and is subjected
to the normal feed line loss. It then is "reflected" back toward the
antenna, again subject to the feed line loss, where some of it is
radiated and some reflected again.
This continues until the power is dissipated. The book "Reflections"
has a very good but somewhat technical explanation.
Therein also is the reference to forgetting about striving for the
"Holy Grail" of 1:1 SWR.
And concentrating on getting it low enough that the transmitter will
supply full power output. Also using the best low loss feed line and
proper matching when possible of the feed line to the antenna.
Dr. Don W4BWS
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