>I've just never seen that power on
accurate meters.<
Accurate RF power measurement isn't quite as easy as it may sometimes appear.
So much so that for European Standards, a measurement uncertainty of +/-0.75dB
is allowed. That does include such things as mismatch errors, too.
One old wive's tale is that you can use a known load and measure current with a
thermo ammeter. Because the ammeter works on heating effect, you can calibrate
it at DC. Unfortuantely, the effects of skin resistance don't help here,
tending to make the ammeter read higher as the frequency goes up. Probably the
most accurate method is calorimetric, using constant liquid flow (a constant
head apparatus) and then substituitng DC to get the same temperature
differential across the inlet and outlet. This cannot be considered a rapid
measurement.........and it does require a tx capable of continuous duty.
Real fun is trying to measure accurately the power in a non 50 ohm (or non 75
ohm some years back) system.
Even the use of a directional coupler has its problems - directivity, mismatch
losses at connectors, etc. They all add to the measurement uncertainty.
vy 73
Peter G3RZP
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