RadioBanter - View Single Post

September 26th 05, 11:03 PM

On Mon, 26 Sep 2005 21:39:27 +0000 (UTC),
wrote:

Jim, that seems inconsistent with your earlier statemetn "No, the SWR
being measured is on the load side of the meter."

The load side is the side with the load, i.e. the antenna, on it.

In the example you quoted with a 100 ohm load on a 100 ohm line, were
the line loss low, and the line long enough to be sure to sample a
fully developed voltage maximum and voltage minimum it would be found
that the VSWR was 1:1.

Not for a 50 Ohm system, i.e. a transmitter expecting 50 Ohms and a
meter calibrated for a 50 Ohm system.

I am sorry Jim, the VSWR is a property of the transmission line and
its termination, and the VSWR on that 100 ohm line with a 100 ohm
termination is 1:1. The VSWR could be *MEASURED* on that line by
sampling the magnitude of the voltage at different points on the line
and it would be found that the magnitude of the voltage was constant,
which means VSWR=1:1.

Yet we would expect the "SWR meter designed for 50 Ohms" to which it
is connected (on the load side) to read VSWR=2:1, so is it measuring
the SWR on the load side of the meter as you earlier stated?

Yep.

No, it isn't.

The SWR meter in your example reads 2:1 when the SWR on the 100 ohm
line is 1:1. Your example demonstrates that a typical SWR meter does
not measure, or necessarily indicate the SWR of the (actual)
transmission line on the load side of itself.

Owen
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