> What do you think about the new MFJ 868 wattmeter that has
> the extra large 6-1/2" meter movement? How good is their
> TrueActive peak readong circuit, and how is the accuracy?
> Do they use another calibrated meter in line to calibrate
> these, or is it done another way? I'm interested in buying
> one, but I'd like to know what's under the hood, and the
> quality of them. I need a large meter now and this looks
> like it may fit the bill.
I haven't seen the meter. I do know several years ago I
pushed them to buy a high accuracy Bird meter and matched
slugs. I would certainly never guess at the absolute
accuracy of anything leaving an "amateur radio" production
environment, but it would have to be less than the accuracy
of the equipment they use. If they used the high accuracy
meter and kept it calibrated, that would be about 2% of
absolute reading. If they have mixed slugs or not maintained
the meter or the person doing the calibration was careless,
who knows what it is.
This is a problem with ANY manufacturer, I'd bet very few
manufacturers of Ham gear own anything beyond a standard 43
that has not been checked or calibrated in years.
If MFJ used the peak detector and directional coupler in the
ATR30 and such, the peak detector is very good. It will read
a few milliseconds of envelope power accurately and hold it
for a few seconds so you can see it. My ATR30's will
actually read the SWR peak caused by hot relay transfer in
an exciter or amplifier (with the meter between the antenna
and the amplifier!), and they will read antenna arcs not
caught by a Bird 43P. The absolute accuracy is another
matter, I'd certainly check it against a known standard.
73 Tom
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