Tom sez,
I have a note I made some time ago in a
reference book that says, "Neglecting dielectric loss, if Zo = Ro+jXo,
Xo is approximately -0.180*Ro*A100*VF/f" where A100 is the attenuation
in dB/100 feet and f is the frequency in MHz. There. Now, at least
for RF, people should be able to generate their own tables.
=============================

Your formula is correct and indeed approximate. But it's not of much use
unless you already know Ro, A100 and VF, all of which vary with frequency.
It is approximate because it ignores a correction factor related to
Sqr{(Wire Resistance) / (Wire inductive reactance)} which varies fast with
frequency.

At sufficiently high frequencies, where Ro (whatever that value may be),
A100 and VF have settled down, all that is necessary is to set Xo equal to
zero and be done with it, just like book-cooking Mr Smith of chart fame did
in 1938.

I produced the table to illustrate the peculiar unexpected effects which
occur with the smaller, popular diameter coax cables as used by amateurs. I
used the words "typical" and "type" in anticipation of remarks such as yours
from already educated people. The table applies closely to RG-58. RG-11, as
you pointed out, is 75-ohm nominal but its characteristics behave in a
similar fashion.

It should be stated that twin, balanced lines of all impedances behave in
the same way except that their HF characteristics extend down to
considerably lower frequencies.

I had in mind there are now LF amateur bands and anyone who may wish to do
transmission line calculations or use his SWR meter at low frequencies
should be warned against measuring errors. It's obvious he wouldn't get much
help from the present un-ending thread on that subject. ;o)

Use programs COAXPAIR and RJELINE3 for design and performance of
transmission lines from power frequencies, audio frquencies, up to UHF using
exact classical methods of analysis. Enter data in practical units and
obtain results in the form you are accustomed to using. Everybody is
familiar with the 1.5-inch diameter wires spaced 12 feet apart striding
across the countryside. Have you ever wondered what a 500-mile length would
sound like with a telephone at each end?
----
=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================





Cheers,
Tom

"Reg Edwards" wrote in message
...
For anyone who may be interested.

Typical of RG-58 and RG-11 type cables.
Zo = Ro - jXo
Xo is always negative.
Angle of Zo in degrees. Always negative.
VF = relative velocity.

Freq Ro jXo Angle VF
------ ------ ------ ------ ------
50 Hz 967 -965 -44.95 0.034
1 kHz 220 -213 -44 0.151
10 kHz 80 -58 -36 0.41
100 kHz 56 -9.3 -9.5 0.59
1 MHz 52.4 -2.4 -2.7 0.63
10 MHz 50.7 -0.76 -0.86 0.65
100 MHz 50.2 -0.23 -0.27 0.66

Smith Chart calculations begin to be inaccurate around 2 MHz and below.
So
do SWR meters.