On Fri, 26 Nov 2004 07:33:04 GMT, Richard Clark
wrote:
.....snip
Reference Data for Radio Engineers, "Mismatch and Transducer Loss,"
"One End Mismatched," pg. 22-12:
Transducer Loss = A0 + 10 ยท log (Pm/P) decibels
where
A0 = normal attenuation of the line
Pm = power that would be delivered were system matched
P = power delivered to the load
Of particular note is that this is one of my references as to the
nature of Source Z which is often neglected in academic treatments
with the presumption that the engineer has already been schooled in
the nature of Real sources (this may shock some complaisant readers
here). However, this citation offers that explicit lesson in figure
10 and makes use of this commonplace characteristic in illustrations
of Mismatch Uncertainty. They go as far as to explicitly offer a
section entitled "Generator and Load Mismatched." You may wish to
review this treatment as it offers the math that would present the
most loss available in a line, above and beyond the typical charts
offered for line loss (which are confined to both ends being matched).
Dear Richard,
I'm finally ready to comment on the above - it is my great fortune to
be blessed with copies of both the Fourth and Fifth Editions of the
ITT Handbook.
I studied over the first 13 pages of Chapter 22 and found that, just
as Wes said, it's entirely the work of MacAlpine as published in 1953.
I went over Equations (1) through (4) in the Mismatch section very
carefully and found no heartburn with anything in that section. This
is NOT to say that I LIKE it, but I do understand it and have no
problem with the math model and the figures. My problems with the two
mismatch topics is simply that I just don't like to call it a loss
when energy that COULD have been delivered to the load does NOT get
delivered to the load as a result of mismatch. For me, lost energy in
a transmission line problem is energy actually lost in the
transmission line, not energy that is being lost elsewhere as a result
of the transmission line not being matched properly. I realize that
I'm probably alone in that thinking, but I like to feel that such
terms as efficiency and losses should be associated strongly with the
item under evaluation, namely the transmission line, and not the
ancillary equipment which feed it or terminate it. Those items get
their own hearings relative to efficiency and losses and those
evaluations do not require the presence of the transmission line. In
fact, those items are usually evaluated as to their performance in
ways that do not in any way relate to how well some transmission line
is or is not working.
However, this is not the nub of the problem that I was encountering -
a problem which has now been partly resolved. At least I think I have
a far, far better understanding of the problem now than I had a few
days ago. The problem centers on the Additional Losses Due to SWR and
how to model them. Since it is, perhaps, more appropriate to continue
that topic under the responses from Wes, I will not go into it here.
I want to thank you and Wes, both, for leading me to Chapter 22 - it
is much more readable than MacAlpine's original paper.
Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk