For real fun, how do you measure the power (with what accuracy?) into a load
such as marine antenna at 2MHz? The dummy load is typically 10 ohms in
series with 250pF: a DC calorimetric method might do to calibrate the resistive
part, but the RF and DC resistances are probably slightly different. How much
loss is there in the capacitor? If you put it on a network analyser, how good
is the answer at this return loss? How accurate is a thermocouple meter? The
books say that you can calibrate a thermocouple with DC, but that ignores skin
effects, which tend to make it read slightly high at RF. I believe
manufacturers actually compensated for this by putting a slightly higher
figure on the
scale for applications where it mattered - which most of the time, it
doesn't.
I have a very hard time with people who insist on quoting numbers to
emaningless digits - like 2 decimal places of dBs, when most of the time,
they'll be
lucky to have measurements to better than 1 dB anyway. But they wil do it,
because the digital readout gives them great resolution!
73
Peter G3RZP
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