Sorry, I must have misinterpreted your earlier posting.

But we seem to now have a "true SWR" as opposed to some other kind of
SWR. And "true SWR connected to the tx output" doesn't have any meaning
at all to me. I also have no idea of what "sample points within the
transmitter" might be. So let me explain what I (and virtually all
published literature) mean by SWR.

If we connect a transmitter to an SWR meter, and then to a long piece of
lossless cable with the same Z0 as the SWR meter, and finally to a load,
the SWR meter reading will be the same as the VSWR on the cable, i.e.,
the ratio of maximum to minimum voltages on the line. This ratio of
voltages is, by definition, the VSWR -- which equals the ISWR, and is
often referred to simply as SWR.

If we measure or calculate the impedance seen looking into the line,
then disconnect the line from the SWR meter and replace it and the load
with lumped elements of the same impedance, the SWR meter reading won't
change(*).

Now, I can calculate the what the SWR meter reading will be under this
condition also. In both cases, the source impedance won't affect the SWR
meter reading, the positions or relative magnitudes of the maximum and
minimum voltages on the line, or the voltage or current within the SWR
meter line section. (This last condition assumes that the net power
delivered by the source stays the same; otherwise, the ratio of voltage
to current, and their phase angles, stay constant, regardless of the
power delivered.)

I have no idea how all this relates to your "true SWR". But do you agree
with what I've said above? If not, I'll describe a couple of simple
experiments which will test it against any alternative view you might
propose.

(*) We can also replace them with a load at the end of a line of
different Z0. As long as we choose the load Z and the line length to
make the impedance seen at the line input the same as before, the SWR
meter will read the same as before -- even though it no longer equals
the actual VSWR on the transmission line. The SWR meter is really
indicating the impedance seen looking into the line, not in this case
the actual line VSWR. (That's the essence of Reg's objection to the SWR
meter designation. Of course, if I connect my ammeter across a resistor,
it's not measuring the current through the resistor, either.)

Roy Lewallen, W7EL


Richard Fry wrote:
"Roy Lewallen" wrote

Let me suggest an additional exercise for Richard and anyone else that
believes that source impedance affects the SWR. (etc)

____________________

Just one sec, please. I didn't say that the true SWR connected to the tx
output connector was affected. I said that the RF power measured at the
sample point(s) in the transmitter can be affected by the source and load
impedances of the tx, for the reasons stated.

The true load SWR does not change under these conditions, but it cannot then
be determined by such a meter. Attempting to do so will yield some value,
but it will be wrong.

RF