[AMPS] Re: Wattmeters

[km1h @ juno.com]

On Sat, 6 Dec 1997 10:23:01 -0600 w5hvv@aeneas.net (Roderick M.
Fitz-Randolph) writes:
>Carl, I know that the Bird is the standard for many military
>installations.... that was where I ran across so many of them.
>
>I recall, while contracted to the Army Security Agency 1st
>Aviation Wing in El Paso, that the maintenance complex had at
>least 10 of them.  On one occasion, we lined them all up and
>put them to the test with the various crystals as I described
>in my prior message.  The test destroyed my faith in their
>accuracy.  Now the repeatability of those may be another story
>entirely.  I can't state on that accord.
>
I would say that you had the worst possible exposure to any piece of test
equipment...the US Army!
Who knows the physical and RF abuse the meters and elements received over
....how many years??

As I mentioned, I have 4 Birds here and about 35 or so elements of all
ratings. My neighbor in the 2 way biz  let me borrow his 3 meters and
slugs last night....it cost me a few beers... The 2 way shop that rents
on my tower also brought over 2 of his meters and a handful of slugs
several months ago for testing.
I have A 2KW CCS Bird load that was made for RCA and is virtually flat
from 1.8MHz to 1.3GHz. 

I ran HF tests at the 100W and 1200W level to 100W, 250W and 2500W slugs.
On 50 and 144MHz I ran 25W 100W and 1500W  into 25, 100 and 1500W slugs
as appropriate. 
On 222 MHz it was 10 and 100W into 10 and 100W slugs.
On 432 MHz it was 10W, 100W and 400W into 10, 100 and 500W slugs.   
On 903 MHz it was 10W and 35W into 10 and 50W slugs
On 1296 MHz it was 1, 10, and 150W into 1, 10 and 250W slugs. 

This required many hours and a second trip to the beer store...the
neighbor made the run and bought!

All 7 meters were well under 5% of FS. For a standard reference I just
picked one of mine which is only a few years old and never been out of
the house.  All power levels could be reduced to 70-80% of FS so as to
not go past the final meter mark. 

All slugs were so close to each other as to be meaningless in respect to
an accuracy percentage.  It is pretty hard to tell the difference between
75W and something under 80W for instance. 

All rigs/amps have been tested and filtered in the past to comply with
FCC regs using an HP-8567A and appropriate couplers and other
gizmos.....borrowed from a lab friend.

Testing with a signal generator and a distributed amp can result in
erroneous readings due to high harmonic content. 

Yes, I have had bad fleamarket slugs that were way off in readings but
when a lot of your business depends on accuracy you tend to take care of
your equipment and be choosy about sources.

If anyone wants in-depth details of the tests private E-Mail me with
specific questions. 



>In regard to the W4 Wattmeter I have, it was put in line with
>a mil-spec 1500 watt dummy load and checked against the readings
>of a Bird wattmeter (at the insistence of WA4VWR who is an
>absolute perfectionist and a terrible cynic when it comes to any
>wattmeter other than the Bird he owns) and the readings were
>virtually identical.
>
>Perhaps my exposure to W4 wattmeters is insufficient for my
>prior posted statement and perhaps the Bird wattmeters I've
>run across at various military installations (and their
>associated PMELs) were not a good sampling.  I have witnessed
>time after time, however, two different crystal units in the
>same wattmeter, being fed by the same source into the same
>load, giving readings that were more than 15% at variance.
>It caused me to become a little cynical about the accuracy.
>Again, I can't state whether the repeatability was in accord
>with their inaccuracy.

I would think that in general the Drake is a good meter but doesnt it
have internal calibration controls? 
The Mirage, Daiwa at least are subject to inaccuracies due to component
aging in the metering cal circuits. 


>Perhaps I just had some bad experiences at Ft. Devens, Ft. Bliss,
>and Ft. Huachuca.....


Nope...probably just typical Army attitudes about something that is not
individually owned, respected and cared for.


>Thanks for the response.  You have made me wonder now if my
>cynicism about Birds is completely accurate!!  Hi Hi.
>
>Best 73,
>
>Rod, N5HV


I now turn the reflector back to parasitic debates and gold flakes. 

73   Carl  KM1H >

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