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December 6th 04, 10:25 PM

On Mon, 06 Dec 2004 19:57:34 GMT, Richard Clark
wrote:

On Mon, 06 Dec 2004 18:03:47 GMT, (Robert Lay
W9DMK) wrote:

I finally created a test load that gives me the higher SWR that I
wanted.
It measures 7.0 - j2008 at 1.8 MHz. I placed that test load at the end
of a 150 foot piece of RG-59/U and measured the input impedance as
38.5 + j 151.6 at 1.8 MHz. The load SWR is 7901 and the input SWR is
10.18.

Solution of the transmission line equations for this particular load
and with coax characteristics of 73 ohms, VF = .646 and an attenuation
of 0.57 dB per 100 feet gives an input impedance of 38.67 + j 149,
which is a very good match to the measured value.

Losses are calculated using the same two methods as reported in my
previous posting, as follows:
1) ITT Reference Data for Radio Engineers, 5th Edition, pages 22-8 and
22-9.

2) The ARRL Antenna Book, 17 th Edition, page 24-9.

Matched line losses = 0.855 dB
Additional losses = 28.087 dB
Total losses = 28.942 dB

I am satisfied that the methods of calculating losses as described in
the two references are in agreement and are valid.

I am also reasonably satisfied that the 1 dB steps that are printed on
Smith Charts as the means of determining matched line losses are
valid, as are the nomograms provided in the ITT Handbook, pages 22-7
and 22-8, above.

Hi Bob,

Congratulations are in order for your effort at the bench, regardless
of outcome.

Congratulations are in order for your chain of reasoning, your
attention to detail, and the obvious refinement of technique that is
now agreeing not only with references, but is also consistent from one
test to the next.

I still see some aberration in the data when you have to drive the
cable Z to 73 Ohms to make the formulas work. It shows that the
generality of the references is good, but with the instance of your
data is a forced conclusion. I don't find that particularly upsetting
as the accumulation of error could easily account for some of the
differences.

You might want to revisit some of Bart's offerings in this thread;
especially his discussion of the effect of Low-R loads as a source of
Hi-Z, Hi-SWR.

73's
Richard Clark, KB7QHC

Dear Richard,

No - I didn't. That was a surprise to me, too! The specs on RG-59/U
say 73 ohms. There are 2 other RG-59 types - RG-59 Foam (75 ohms) and
RG-59A, also 73 ohms.

C'est la Guerre!

73,

Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

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