It has been suggested that steady state VSWR measurements on a
transmission line are influenced by the source to line match, and that
the measurements are not valid unless the source is matched to the
line.

That seems in conflict with textbooks that suggest that the reflected
wave is entirely determined by the conditions at the load end of the
line, and that the conditions at any point x on the line can be
determined from x, Zo, the load impedance, and the line's propagation
constant.

So, I have performed a small experiment.

I have a tx - 1m of RG58 - T-match ATU - 1m of RG58 - MFJ949E ATU -
20m RG6 - dipole.

The MFJ949E incorporates a crossed needle VSWR meter, and is used in
the 'thru mode, so it is just a VSWR meter.

I have tried tests at three frequencies where the VSWR meter on the
ATU indicated 1.1, 2 and 6, and tuned the first ATU for low VSWR on
the tx's inbuilt VSWR meter. Some would suggest that this means that
the tx is matched to 50 ohms, but I am not endorsing that view. I have
then varied the ATU's output capacitor over its full range, and
although the '949E's needles vary, they always cross on the same VSWR
line. (I have only considered readings where the needles are upscale
of 30% for accuracy reasons).

In this experiment, the large variations that I made in source
impedance did not noticeably influence the measured VSWR at low,
medium and high VSWR readings. The observations would not suggest that
steady state VSWR is influenced by the source impedance.

Comments?

Owen
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