Reg Edwards wrote:

"Ian White wrote
Yup. It measures the reflection coefficient of whatever impedance is
connected to the port on the opposite side from the transmitter.

=====================================
No, it doesn't.

It measures the MAGNITUDE of the reflection coefficient. It discards
the information which is contained in the phase angle of the
reflection coefficient.

Sorry, I left that important word out.


As a consequence the only use which can be
made of the magnitude is to calculate the SWR on an imaginary 50-ohm
line.

Agreed. SWR has become a number that indicates the general "goodness" of
an impedance match. It is almost always determined indirectly, by
actually measuring something else and then calculating an SWR value.

The only way to measure VSWR truly and directly is to find the points of
maximum and minimum voltage along the line, and measure the ratio of
those two voltages. That is the classical definition of VSWR, but hardly
anyone measures it that way, because it requires physical access to all
points along the line. But if they do, then...

The SWR can be used to calculate the magnitude of the
reflection coefficient.

Engineers swap freely between the different available ways of expressing
the "goodness" of an impedance match, choosing whichever one is the most
convenient (or conventional) for the application.



--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek