On 20/12/2022 01:38, Bob McGraw wrote:
Use an antenna analyzer to determine the actual complex antenna impedance. I've always viewed SWR as more of a hocus pocus value, easy value to obtain, but very broad in definition as it is a ratio between two impedance, both usually unknown.
Whilst I'd agree that its usefulness is overstated, it is not the ratio of two impedances, and one of the impedances is generally known (unless you are measuring the the Lecher line way, by actually finding the voltage peaks and troughs on an open line, of unknown characteristic impedance).
I don't think the professionals have used for a very long time. They prefer s parameters, or if they want a single number, they use return loss. It is basically only heavily used in the amateur and CB communities.
Generally it is defined assuming an ideal transmission line, with a purely resistive impedance. and in that case, the only time that it equals a ratio is when the load impedance is also purely resistive.
The main advantage of SWR is that it can be physically measured without having to use anything other than the magnitude of the voltages read (i.e. no phase information). But this means that the same SWR can be completely safe or destroy a PA, depending on the phase information.
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