In message , Reg Edwards
writes

"Roy Lewallen" wrote

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.

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It is at this point where impressionable novices are led astray by old
wives, never again to return to logical thought on the subject.

They imagine that because the meter happens to indicate the swr on the line,
the meter is actually responding to the swr on it. Whereas the meter is
actually responding to the modulus of the reflection coefficient caused by
the line's input impedance regardless of what its Zo may be. The act of
making the line's Zo and the meter's resistance both equal to the
transmitter's designed-for load resistance, has put additional infomation
into the system. Cooking the books!

If there's an SWR to be indicated it is on a long line between meter and the
transmitter. In the absence of such a line the meter wastefully discards
half of the information it is presented with and indicates the modulus of
the reflection cofficient. A more appropriate name is TLI.
----
Reg, G4FGQ



Would this help?

On the subject of whether the TX impedance affected the SWR reading, I
propose the following practical test:
Using standard CATV bits and pieces, connect up the following-
Signal source directional coupler #1 directional coupler #2 load.
DC#1 picks off the forward signal, DC#2 picks off the reverse.
Use a spectrum analyser to measure signal levels.
Beforehand check the DCs for go directivity, and chose a frequency where
it is best (at least 25dB). This will probably be around 20MHz.
With good load, measure forward and reverse signals.
Repeat with known load mismatch.
Screw up source impedance (eg add T-piece at source o/p, and
double-terminate).
Repeat the above.
Think about what the results mean.

Ian.



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