RadioBanter - View Single Post - Length of Coax Affecting Incident Power to Meter?

August 14th 03, 01:12 AM

(Tom Bruhns) wrote in message om...
(Dr. Slick) wrote in message . com...

impedance, you can determine the SWR on that line. But your "SWR"
meter isn't really an S11 meter; at best it's a |S11| meter.

Of course. We have no phase information. Only the magnitude of
the voltage reflection coefficient.

This also brings up another point: do YOU define S11 to be the same
as reflection coefficient?

Cheers,
Tom

I define the S11 as the complex impedance, which never changes,
but S11 can also refer to the magnitude of the reflection coefficient
at a particular phase, AT A PARTICULAR NORMALIZED REFERENCE IMPEDANCE.
If you define the reflection coefficient as having phase
information, then yes, they are the same, but only at a particular
reference impedance.

Change the reference impedance, and you will have a new reflection
coefficient, but the complex impedance will still be measured to be
the same.

You can do this is Motorola's Impedance Matching Program (MIMP).

What this all comes down to is that your 50 Ohm SWR meters only
measure reflected powers after it, not before, so any mismatch from PA
to reference impedance (50 ohm coax from PA to meter) is not measured.

Slick