Dear John S: My comment of a few days ago was written under the assumption
that you wished to know the characteristics of the TL. It has developed
that you wish to measure the impedance of an antenna at the end of a piece
of coax.

The procedures for removing the effects of a fixture, which I expect to be
in the AN and require a short, an open, and a known load, may also be
applied to a piece of coax. The result is the ability to remove the
presence of the coax and be left with the antenna's impedance.

I do this in an automated way with the "calibration" feature of the AM4170.
One scans a span of frequencies three times storing information about what
the coax looks like with a short, an open, and (usually) 50 ohms at the far
end. This takes some time depending on the size of the frequency span and
the step size. The stored numbers (stored in a very inexpensive, tiny
computer) are then used automatically to calculate (over the same span) the
actual Z at the end of the coax.

Doing this procedure by hand, which I have done using the numbers measured
by a GR bridge, is labor intensive. Before the advent in 1972 of the HP35,
it was real pain. One did not use very many frequencies! It appears that
you are interested in only one frequency.

Comments about choking common mode are right on target. Owen Duffy is one
of the good guys.

73, Mac N8TT

P.S. Do you have a call sign?

J. C. Mc Laughlin
Michigan U.S.A.
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