I can confirm that a professional Bird 43 wattmeter is
much, much more linear than any amateur meters I've tried.? +/- 5% of FS
is their spec if I recall correctly.? But to get that you need various
slugs to cover your frequency and power needs (can be expensive).? I
have several 43s here with elements for HF, VHF, and UHF at my power
levels.?
I don't think
the linearity problems with the amateur meters is really a big deal in
their normal operational use.? I check (and calibrate if needed) across
the bands against one of my Bird 43s for the likely power levels where
they are installed.
For
example, my operating desk wattmeter is a mystery "Macaw" brand unit
that I rebuilt when its DC and calibration board started to get
intermittent.? It reads quite close at the likely power levels from
those transmitters:? 100, 200, and 800-1000 watts.? I set it up so CW
signals read the same on average and PEP, and on SSB and AM the PEP
readings make general sense so that's good enough for the operating
desk.?
But I would NOT
want to use one of the amateur meters on the repair and homebrewing
bench.? I have a Bird 43 and a dummy load set up there at all times.? I
don't want unreliable metering to make me chase non-existent problems.? I
added a peak-detecting board to this 43 and added a switch to choose
AVE/PEAK.? The mod does not involve the RF or sampling, just the DC to
the meter.
I have only
confirmed the performance of the Bird 43 meters against each other and
by swapping the slugs around.? I have one Bird that I bought brand new
so I am felt good when the old beater meters agreed with it.? I have not
used other gear calibrated to external standards to confirm the Birds.
Steve WD8DAS
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