"Reg Edwards" wrote in message
...

"Jerry Martes" wrote
I'm writing this to represent the "other side" of an arguement
that states
that VSWR *cant* be measured. I claim that VSWR *can* be measured
and that
VSWR can be used to identify the impedance terminating the
transmission
line.
========================================

The only way to measure SWR on a transmission line is to run a
voltmeter along it. At least TWO measurements are needed. Not ONE.
And line length is involved.

The voltmeter readings will indeed tell you what the SWR is. But
nothing else. It will be possible to calculate from the readings and
the distance between max and min what the velocity of propagation is.

But it is essential to add extra critical information before anything
else can be deduced. Without this EXTRA information knowledge of the
SWR (if it can be obtained) is useless. The so-called SWR meter does
not and cannot provide this information.

To calculate the terminating impedances from the SWR it is neccsary
also to know the line impedance, its velocity and the exact locations
of the max-volts and min-volts relative to the ends. The meter will
not tell you.

And the foregoing is on a line which exists only in one's imagination.

I am sorry to repeat, the indications of the SWR meter apply only to
the input impedance of the line from the transmitter to the antenna.
The meter, in itself, tells you nothing about what is happening to
conditions along the line. It certainly tells you nothing about the
antenna's input impedance which is of primary interest.

IF, BY SOME MEANS, YOU CAN MEASURE SWR, then there is much more
information needed before the performance of the system can be
predicted.

The funny thing is - the performance of the system can be deduced
from the extra information without reference to the SWR. The whole
business is laughable.

Just change the name of the meter and all will become clear.
----
Reg, G4FGQ.

Hi Reg

I have no understanding of why you find it important to state things that
are not true about VSWR. VSWR *can* be measured. It is clear to me that
you know that the Complex Impedance terminating a transmission line can
determined by measuring the VSWR. Sure, it requires the position of the
voltage mins (or maxs) be identified, with the load and then with a short
ckt., and a Smith chart to be used for quick/easy identification of the load
impedance. But, is that so much calculation that you find it necessary to
state " IF, BY SOME MEANS, YOU CAN MEASURE SWR, then there is much more
information needed before the performance of the system can be
predicted".

The load impedance isnt "predicted". It is actually *determined* with an
accuracy associated with the precision of the test equipment.

I consider measuring VSWR on a transmission line to be an excellent method
of determining load impedance.

Jerry

Jerry