Richard Harrison wrote:


In my long rxperience, I`ve found it`s never profitable to argue with
Terman. He is as close to infallible as any wrirter I`ve ever read.


All of the handy-dandy transmission line formulas
that we have been using for many years apply
specifically to lossless lines.

A line with loss has a complex value of Z0. If the
imaginary part of Z0 is more than a few percent of
the real part we should use different methods.

One famous example:

Pload = Pforward - Preflected

is one that has to be treated with suspicion if
the line has appreciable loss (complex Z0).

Another is :

SWR = [1+|rho|]/[1-|rho|]

At high values of rho close to 1.0, SWR becomes a
totally useless concept. This is true regardless
of which formula for rho that we use.

We use the Smith chart outer circle to plot
lengths of transmission line, for example stubs
and matching transformers. We assume these lines
taken by themselves are lossless and have infinite
SWR (the outer circle of the Smith chart is the
"locus" of infinite SWR).

If we know the matched loss of a particular coax
(dB per 100 ft) it is far better to use a math
program and calculate everything, if the matched
loss is not negligible. The computer is much more
revealing than the Smith chart when line loss is
significant.

Bill W0IYH