----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "Mike Schatzberg" <cherokeehillfarm@earthlink.net>; "Amps Reflector"
<amps@contesting.com>
Sent: Monday, July 17, 2006 6:00 AM
Subject: Re: [Amps] transformers
>
>> Well, I stated what I have used for measurement, and I
>> realize that the Bird
>> and Nye Viking are not a Hewlett Packard. I can accept
>> that both meters may
>> be off by 10%, even though their accuracy is supposed to
>> be about half of
>> that.
>
> One thing I have learned doing RF measurements almost every
> day for 30 years or more is RF measurements are tougher to
> do than most imagine.
>
The most important thing that I have learned about RF (power)
measurements is the the difference between accuracy and precision.
Use a meter with a precision scale that is accurate at zero DBM and
make all your measurements at that level. If you want accuracy you
should use known calibrated reference attenuators to bring your indicated
reading to zero DBM or close enough so that you can use the precision scale.
Take your measurement from your calibrated standards. Not the meter.
> The accuracy of a Bird 43 meter, when properly calibrated
> and used, is + or - 5% of full scale anywhere on the scale.
> Since they do not manufacture a 1500 watt slug, the best we
> can rely on is + or - 125 watts at any power level with a
> properly calibrated 2500 watt slug. Many people would be
> surprised at how far off a new Bird 43 and slug combo can
> be.
>
I once had the the job of fending off the test equipment vendors hawking
their power meters to the newbie engineers. I always went with the same
brand because the others would lose precision at the range edges. At that time
in my career the digital display types were the latest trend and they sold like
flapjacks. My conversion from analog movements to digital displays was painful.
ATE and the 488 bus setups excacerbated the problem. For my own work I
use a pair of HP-435B meters and a good set of calibrated pads.
As for PEP. I always felt it was a marketing term. Never bothered with it
and from the lengthy discussion here I have learned nothing new.
> I know of several manufacturers that had great difficulty
> making 1500 watts (measured by accurate means) with pairs of
> 3-500Z's when only 100 watts of exciter power was available.
> HV had to be over 3500 volts.
>
> 73, Tom
>
>
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>
Mike k1ern
" if you give a man a fish, he will eat for a day. But if you give a man a
rifle,
he doesn't have to eat fish"
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