"W5DXP" wrote in message
...
Consider the following two examples:

1. The source is generating 100 watts and 20 watts of the 50 watts of
incident reflected power is being re-reflected in phase from the source.
The forward power meter reads 120 watts. The reflected power meter reads
50 watts.

The conventional rule-of-thumb has the source generating (100-30)=
70 watts since it is dissipating 30 watts of reflected power.

2. The source is generating 110 watts and 10 watts of the 50 watts of
incident reflected power is being re-reflected in phase from the source.
The forward power meter reads 120 watts. The reflected power meter reads
50 watts.

The conventional rule-of-thumb has the source generating (110-40)=
70 watts since it is dissipating 40 watts of reflected power.

How can you possibly distinguish between the above two identical
conditions
caused by different source impedances?
--
73, Cecil, W5DXP

Cecil,

I actually did a test along these lines. Believe we discussed that some
weeks ago before I did it.

1/4 wave 50 Ohm line shorted at the end. Freq ~ 2 MHz

50 Ohm generator in series with a 75 ohm resistor at the other end.

Looked at both ends of the 75 Ohms, both to ground, and differential.

At resonance, all voltages were in phase.

Unfortunately I used very low loss line, but to a good approximatio, the
only power supplied by the source could be explained by cable loss, and all
reflected power was re reflected. It would be interesting to do this with a
total source impedance of 50.

BTW, I also did the thing with measuring VSWR and then changing the source
impedance. Power changed, VSWR did not, for either 1:1 or 1.7:1.

Tam/WB2TT