[AMPS] Bird Wattmeter Error on all bands

[Rich Measures]

>At 09:26 AM 6/1/98 +0000, you wrote:
>
>>The standard Bird 43 meter meter and slug has a published error of 
>>plus or minus 5% of full scale anywhere on the scale.
>>
>>(That's why a Bird often shows incorrect SWR readings when a high 
>>power slug is turned around.)
>>
>>If you have a 2500 watt slug, and are reading 1500 watts forward 
>>power into a pure 50 ohm load, the actual forward power is anywhere 
>>from 1625 watts to 1375 watts if the meter is within tolerance. + or 
>>- 5% of 2500 is + or - 125 watts, and that is the tolerance ANYWHERE 
>>on the scale ANYWHERE over the slugs range.
>>
>>If the a Bird 43 indicates 150 watts reflected power with a 2500 watt 
>>slug, the actual reflected power can range from 25 to 275 watts. 
>>
>>73, Tom W8JI
>>w8ji.tom@MCIONE.com
>
>
>Yes, Tom, your statement is very evident in all Bird publications. You
>missed my point...in ADDITION to the +/- 5% error, you must add ANOTHER
>10% to the power reading when using a 2-30 mhz slug below 2 mhz.  Worst
>case at 1.8 mhz with a 2-30 mhz slug is a 15% low reading.
>
For the case Tom Rauch cited, using 150w and a 2500w FS slug, the 
allowable neg. error was 25w/150w = -83%.   I agree. .  For <2MHz 
measurements, an additional -10% tolerance applies.  10% of 150w is 15w.  
Thus, the allowable reading would be 25w minus 15w =s 10w.  Thus, 150w 
can legally read 10w on the meter, so it seems to me that the allowable 
neg. error limit is -93% for <2MHz measurement of a 150w source.  .  



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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