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Old October 8th 15, 10:57 AM posted to rec.radio.amateur.antenna
John S John S is offline
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Default Transmission line loss under mismatch explanations

On 10/8/2015 4:40 AM, Jeff wrote:
Anyway all of the article can be blown out of the water by some practice
measurement of a real life situation, which will show that a 3:1
mismatch will produce the same loss regardless of whether it is Zo*3 or
Z0/3 when you are talking about feeding an antenna.

Jeff


Great, Jeff! I would support your suggestion to make measurements. All
you need to do is set up his scenario and collect some data. Please use
his identical set-up to confirm or refute his results.


If you have understood what I have been saying at all then you would
understand that I am not refuting his results (at least to a first
approximation). What I am refuting is the extension of his results to
the 'normal' case of feeding an antenna, which he tries to do in the
later parts of the article.



Okay. He says in his section "Failure in thinking":

"The forward and reflected waves give rise to E and I that vary along a
real transmission line, and the loss is due to I^2R loss in conductors
and E^2G loss in dielectric, so the loss in any incremental length of
line depends on E and I at that point. The loss in any line then is the
sum of the incremental losses due to varying E and I along the line."

His use of "real transmission line" now turns my attention to the
practical situations. It seems to me that he means to point out that the
losses are not smoothed over the length, but the final averaged result
can be influenced by the incremental, summed losses rather than just the
reflection coefficient which the equations use.

In reality you do not need to do the experiments, they have been done
many times, and the loss in a feeder under mismatch conditions is well
know and documented. It is these results that the author is challenging
from the wrong standpoint of a short line which is not extensible to
other cases.


Please point our where he extended his analysis to other cases.

Jeff


Well, you suggested that the experiments be performed and I applaud you
for that. If you can provide data on experiments which refute his
analysis, please do so.