Let's not lose sight f the fact that an Accredited Test Laboratory is expected
to have a measurement uncertainty to a 95% certainty level for conducted power
of less than +/-0.75dB. That takes into account cable losses, mismatch losses
in loads, connectors, etc., but give you some idea of the problems even in
professional lab set up.
Q measurement depends on whether you are measuring real Q or apparent Q: the
latter is fairly easy to measure by very loose coupling and a bandwidth
measurement. But then you have to ask yourself 'For what reason do I need a
very accurate measurement of Q?' It can be a bit too easy to get yourself hung
up on measurement uncertainty if you don't figure why you need the answer to
that accuracy. Real Q on an echo box is relatively easy to measure, but not
something very applicable to most of us...
Working Q, as in a tank circuit or antenna tuner, is another matter as far as
measurement goes. Not an easy measurement, but why would you want to bother
knowing, other than to a first approximation, which you can get by doing a few
sums?
73
Peter G3RZP
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