"The SWR meter does not compare what it sees on it's input against it's output connector. It compares the ratio between the incident wave and reflected wave."
It doesn't do that comparing thingy between it's input and output, really? Then it shouldn't make any difference how you connect that SWR meter to the transmitter, since it's only measuring stuff on one side of the meter. But then, where does that incident wave come from but the input/transmitter side of the meter? And where does that reflected wave go back to, but to the output of the transmitter?
"About the only change you'll see if the output impedance of the device in front of the meter was off would be a reduction in the power transfer efficiency."
I agree, you would see a reduction in efficiency of that transmitter, in relation to it's output power level because of a not good load impedance, it's not seeing a 'good' load impedance that it likes. But that's indicated by that SWR meter showing an increase in SWR. That ratio of incident to reflected power changes, the reflected power goes up, the incident power goes down, meaning the SWR goes up. (You can substitute amplifier for transmitter in that, works the same way, just a different reference point.)
Now, it the transmitter's output impedance is what changes instead of the load's impedance, you will see the exact same thing happen. So how do you tell which changed? By measuring the loads input impedance by some other method. If there was no change in that load's impedance, then guess where that change had to occur!
That SWR meter -DOES- make a comparison of the impedance on the input side and the impedance on the output side of that SWR meter. If the change isn't on one side of it, it has to be on the other side of it. That meter also is only 'good' for 50 ohms impedance systems, it's made that way. All SWR meters are made to be used with a certain characteristic impedance, which in most cases is 50 ohms. Want to use a 50 ohm SWR meter to get measurements from a non-50 ohm impedance? You'd better start doing some impedance transformations at the input and output of that meter. Or, just use a forward/reflected reading watt meter and find the SWR by formula (odd, where have I heard of that happening before?).
- 'Doc
