Michael,
I have read the article in question and as near as I can tell he
is correct in his ultimate conclusions. I'll try to answer your
questions in less than 12 pages of tortuous math to support an
"around the barn to get to the parlor" approach to the problem.
To: <towertalk@contesting.com>
>Date: Thu, 18 Mar 1999 05:43:34 +0000
>From: Michael Tope <W4EF@pacbell.net>
>
>Tom,
>
>I haven't seen Dr. Best's article or even read Maxwell's book
>for that matter, so I am coming somewhat from a point of
>ignorance. My questions is, are the graphs that you see in the
>ARRL handbook and ON4UN's Low Band DXing book, which relate
>mismatch loss to matched loss, correct generically or do they
>contain an implicit assumption about the loss mechanism
>(dielectric loss due to displacement current in the dielectric
>versus I^2R heating losses in the conductors)? In other words,
>is the math kind to us in such a way that you can accurately
>predict the mismatch loss armed only with a "one size fits all"
>graph and a measurement of the matched cable loss, or do I need
>the additional knowledge of what is going on inside the cable to
>make an accurate prediction of the mismatched loss?
>
As long as you are operating outside Tom's "short line" zone, the
Handbook charts are correct. There are no magic assumptions
about the nature of dielectric or conductors built into them.
They are valid so long as the power offered to the system is low
enough that all the pieces are operating in their linear region.
In fact outside Tom's short line zone, and assuming some matching
device at the input end of the line, there are only two (three
depending on what you are calling the "system") pieces of
information necessary to determine the total system losses and
how much of this loss that is due to operating a lossy coax line
at a specific value of mismatch. You need only know the feedline
to load mismatch, the total loss the line would have if properly
matched and if the matching device is not part of the
transmitter, the loss in the matching device.
The math to do the calculation is very straight forward and a
simple set of two or three very low math intensity formulas can
do the job. If there is much interest in the formulas (after all
the handbook charts do work), I can ASCIIfy them and post them in
another message.
Snip...
>
>73 de Mike, W4EF...........
>
73, Eric N7CL
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