[Elecraft] OT: Bird Wattmeter "meter failures"

[lmarion]

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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