[Antennas] coax 'sweet length'

[Robert Lay]

Dear Danny,

Here are extracts from The ARRL Antenna Book, 17th Edition:

Page 24-12 -
"When the line length is an even multiple of 90 deg (that is, a multiple of
1/2 lambda), the input resistance is equal to the load resistance regardless
of the line Zo. As a matter of fact, a line an exact multiple of 1/2 lambda
in length (disregarding line losses) simply repeats, at its input or sending
end, whatever impedance exists at its output or receiving end. It does not
matter whether the impedance at the receiving end is resistive, reactive ,
or a combination of both. Sections of line having such length can be added
or removed without changing any of the operating conditions, at least when
the losses in the line itself are negligible."

Page 28-3 - (On the topic of SWR circles on the Smith Chart)
"The complete circle around the edge of the chart represents 1/2 lambda.
Progressing once around the perimeter of these scales corresponds to
progressing along a transmission line for 1/2 lambda. Because impedances
repeat themselves every 1/2 lambda along a piece of line, the chart may be
used for any length of line by disregarding or subtracting from the line's
total length an integral, or whole number, of half wavelengths."

If you do not have the reference text,  I can scan the relevant paragraphs
and send them to you off-line.

My best guess is that there has been a misunderstanding between yourself and
Roy. I know you too well to think that this is an irreconcilable issue.
Let's keep working on it until we see some daylight. I also have another
reference that I am trying to translate into its essence - i.e., the
transmission line equations themselves. They reduce to something quite
easily managed when you set lambda to 180 deg (pi radians).

Hang in the, Danny!

Bob Lay (W9DMK), Dahlgren, VA
w9dmk at crosslink.net
Home Pages: http://www.qsl.net/w9dmk
http://zaffora.f2o.org/W9DMK/W9dmk.html
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