[Elecraft] OT: Bird Wattmeter "meter failures"

[N2TK, Tony]

Leroy,
Totally agree with you. In the commercial RF generator business we used Bird's. But every 6  months we calibrated the unit with a calorimeter for the specific frequency of our generators.  We would make a new meter face and also tape the slug to the particular meter so it couldn't be changed.
We bought a lot of slugs. It was not unusual for a brand new slug out of the box to be off >30%. Birds are good as a loose measurement device.

By the way, one year at Dayton I picked up a couple used Drake W-4 wattmeters. They were surprisingly accurate on 20M.
Today there are better choices in wattmeters for the shack.

73,
N2TK, Tony

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of lmarion
Sent: Saturday, November 21, 2015 11:35 PM
To: Ron D'Eau Claire <ron at cobi.biz>; elecraft at mailman.qth.net
Subject: Re: [Elecraft] OT: Bird Wattmeter "meter failures"

The Bird wattmeter is a coarse and loose measurement device.
It is the most overrated power meter, especially in the amateur community.
The calibration is only possibly  five percent at a single frequency, usually the center frequency of the slug. Away from that frequency it rapidly goes way off , I have seen as much as 30% in the range of the slug.
It’s a very rugged meter, used to confirm a rough level of RF. It is better at confirming a SWR, as the frequency error is the same in forward as in reverse.
I have seen many new slugs that could not be calibrated to >10%  over a 10Mhz range.
    Accurate power meters have frequency  calibration factors for each power head sensor., in modern ones it is sometimes in a PROM in the sensor head.
I have told this story many, many times in the ham community.
Bird marketing may be the reason for the ridiculous reverence for them in the ham community. You can drop one from the tower and it will probably work as poorly as it ever did,  one of their only strengths .

Leroy   AB7CE , retired NIST calibrations standards technician.



-----Original Message-----
From: Ron D'Eau Claire
Sent: Saturday, November 21, 2015 8:44 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] OT: Bird Wattmeter "meter failures"

If you want to rely on a piece of test equipment it MUST be serviced and calibrated regularly. The Bird wattmeter I carried as a marine radio service tech was calibrated annually without fail, or immediately after I dropped a slug! Banging on a slug it the quickest way to change the calibration.
That's why they are kept in the spaces provide on the meter housing when not in use.

All of the Birds I've seen in Ham's hands have calibration stickers many years old.

73, Ron AC7AC


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