TopBand: [AMPS] Bird Wattmeter Error on all bands

[bjorn.waller@ffvmatteknik.ffv.se]

NAA10649
Sender: owner-topband@contesting.com
Precedence: bulk
X-List-Info: http://www.contesting.com/topband.html
X-Sponsor: W4AN, KM3T, N5KO & AD1C


Hi,
I have been calibrating quite a few of these in recent years and can say
the following:

the Bird  (43) wattmeters can show wrong power:
	1	Because of NOT terminated into a 50 ohm load.
	2	Because of that the element is out of specification !

The Bird (43) slugs are equipped with sensitive UHF GERMANIUM DIODES
(1N82AG).
These diodes are drifting in their behaviour /caracteristica (with
time), so a reading out  of the specified ± 5 % is easily reached.

As the matter of fact, some few large quantity customers have
RE-SPECIFIED the slugs for ± 7 % !

(Out of 1000 ordered slugs it happens that some 300 of them has to be
shipped back to BIRD; OUT OF SPECIFICATION)

New type of elements (the ones without any rivets on the front plate)
can be adjusted, by means of a potentiometer inside. This potentiometer
can be accessed if You remove the aluminium plate that is glued to the
brass body.

The normal way to calibrate an RF wattmeter is to use a traceable
calibrated DIRECTIONAL COUPLER, together with an RF-level meter that
also is traceable calibrated.

If You try to replace a diode, it is very hard not to damage it further.
It will only survive some 20 V and a heat temperature well below 200
degrees C.

To measure RF power accuratly is not an easy task !

73 de SM6EHY, Bjoern
At: bjorn.waller@ffvmatteknik.ffv.se    (work)



--
FAQ on WWW:               http://www.contesting.com/topband.html
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com