On Tue, 29 Nov 2005 21:35:33 GMT, Cecil Moore wrote:

Owen Duffy wrote:
So what is the answer to your example, the load Z, with and without
consideration of the losses?

Sorry, I just got a new Dell and don't have my software loaded.
A quick pencil whipping of a Smith Chart graph yields a
load around 1140 - j1900 ohms which would be about right
for a 145 ft. dipole on 40m.

You didn't differentiate between the lossy and lossless solutions. The
difference isn't very much, I figure about 1100-j2000 vs 1000-j2170
which is real hard to resolve on the Smith chart. Smith chart programs
solve the same tranmission line problems as underlies the Smith chart,
but using a program provides much higher resolution, and the
convenience and accuracy benefit of not having to find the solution in
a normalised domain.

The Smith chart does not directly indicate the mismatch loss in the
general case.

My online calculator at http://www.vk1od.net/tl/tllce.php produces an
answer (considering loss) of 422.87-j1441.91 if the transmission line
was 90' Wireman 552 and using Wes's characterisation of 552 for
derivation of the fundamental line parameters (slightly different Zo
to yours). Indicated line loss is 0.93 dB. (SWR is not used to arrive
at the solution.)

Dan's TLD gives 432.7-j1459.0 using a slightly different transmission
line approximation, and independently deriving the model from Wes's
characterisation. Indicated line loss is 0.93 dB.

This demonstrates the sensitivity of the result to very slight
variations in line parameters, consideration of loss, and the
approximations used in modelling.

Owen
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