Tom's reply to the PowerMaster wattmeter drove me to inquire
as to the calibration science behind them, and below is the
listed response:
" As shown in Table 2, the PowerMaster
is quite accurate over a range of frequencies, power levels and signal types.
The test signals include key down CW, CW at a 50% duty cycle (60 WPM dits) and
two tone (PEP). The HP microwattmeters themselves are rated at Â5% accuracy,
so any variations are well within measurement tolerances.
During the PEP testing we discovered that the PowerMaster is more accurate for
PEP measurements than the Bird 4381 computing wattmeter we normally use for
comparison.
The Birdâs spec is Â8% of full scale for PEP measurements. The Lab used its
HP microwattmeter and the 14 MHz 2-tone test ïxture that we use to check
ampliïer IMD to verify the measurements. The PowerMaster was pretty much
right on the money.â
Basically we do calibrate it very well, and we have taken the steps to remove
the uncertainty in our measurements and or reduce them to the +/- 3% level or
better. The one thing that we learned early on using the "slug" type line
section meters is they are all really pretty bad. We even went to one company
(name withheld) and purchased a "calibrated meter and slugs".
We found out it was way off, and not ever reproducible in it readings due to
temperature issues. We ended up finding that the 50 couplers we calibrated it
in the morning at 65 degrees, were all different when we retested them in the
afternoon when the temperature in the building was a higher 75 degrees. That
is when we got serious and purchased a NIST traceable meter, calibrated
attenuator, and "Thermocouple probes". Then we calibrated out our test cables
(loss), and other fixture properties.
We are for sure much more accurate then a Bird, which is 10% of full scale
readings. Thatâs 500W on a 5KW slug! And on top of that they don't have a
temperature spec which can add another 10% error on top of that.
Tell your friend to try this, put in a 1KW carrier into his favorite slug meter
and measure the power, now while watching it turn on a hair dryer on low heat,
start heating up the slug and body. It won't take long, you can literally see
the meter move.
Now try it on a PowerMaster!
Also I might add that the PowerMaster was not designed to just be a peak power
meter, it is a station monitor with active alarms. Used properly it will save
some big expensive tubes.
Please feel free to share this with the good folks on the AMPS reflector, and
if anyone would like to discuss this we will be happy to do so.
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