In a message dated 21/03/2005 15:27:42 GMT Standard Time,
wa6fgi@sbcglobal.net writes:
The readings of power out on bird wattmeter have been as accurate as can be
obtained.
That is a matter of some contention!
Firstly, as someone said, it doesn't really matter that much as far as we're
concerned. Secondly, 5% is 0.22 of a dB: especially at V/UHF, mismatch
errors and cable losses can eat all that up, so exactly what is meant by 5%
needs
considering. Plus the Bird is rated to 5% of full scale, so the real accuracy
depends where on the meter scale the power happens to be sitting.
I suspect that ratios are fairly accurate, so if you measure 50 watts one
way and 40 watts the other, the actual SWR is fairly accurate (something I did
today to check the cables going up the tower, with the ends open) and you can
get a fair intimation of the cable loss. But primary or even secondary
standard, it ain't!
One of these days, I might get me an HP power meter: I believe they are more
accurate, as they work on a different principle. By the time you've put in
all the attenuation that needs, I suspect you won't end up with a much better
answer than the Bird.
73
Peter G3RZP
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|