Peter,
What I've found is there's a lot of meters out there just as good as, if not
better than a Bird 43. Bird uses the simple principle of using a strip line
(their term thru-line) to measure power. That's also the reason they have all
those different slugs for different bands as the stripline method isn't very
widebanded. A transformer type is more widebanded and accurate over a wider
bandspread than a stripline type. Even they have their band limits and the
toroid core material has to be changed when that happens. Some of the old Drake
Heathkit, and other meters that used the same method I've found just as
accurate. The "peak reading" ones without the true reading circuit merely added
a small electrolytic capacitor to charge up so the meter had time to read the
peak power so to speak. True peak circuits though use op-amps to measure it.
Philco had a peak reading meter that used tubes along with a thru-line
arrangement like Bird. I have one of those here. Still, if the meter face
is off, or the meter itself not calibrated right on along with the percentage
allowed, they're not that accurate. A calorimeter as you mention is the closest
possible way to do this.
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/8/06 at 5:04 PM Peter Chadwick wrote:
>Roy said:
>> Accuracy is essentially that of the voltmeter, typically 3 percent.<
>Have you calibrated that?
>For Type Approval testing, many standards call for the measurement of
>power to +/-0.75dB for a measurement certainty of 95%. That's in a
>certifed laboratory, with traceable calibrations, and works out to
>+/-18.9%. Now if it is that easy to measure to 3%, why don't the standards
>call for better?
>For radiated power, a measurement to 95% certainty requires +/-6dB - a
>value detrmined by taking aknown tx and antenna round a string of
>certified labs and measuring. Frightening.
>The most fundamental way of measuring power must be calorimetric. I
>believe that if you have a thermally insulated load and use it to heat
>water, and repeat with DC in the load to get the same temperature rise,
>(with constant ambient) you can probably get within a few percent....
>73
>Peter G3RZP
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|