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[TowerTalk] Re: [AMPS] Bird Wattmeter Error on all bands

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Subject: [TowerTalk] Re: [AMPS] Bird Wattmeter Error on all bands
From: (Tom Rauch)
Date: Mon, 01 Jun 1998 09:26:23 +0000
To: <>
> Date:          Mon, 01 Jun 1998 00:07:40 -0500
> The standard Bird HF slugs like we all use are marked 2-30 mhz. I
> always figured that 1.830 mhz was close enough to the edge to not
> make any difference. Not so...there is a 10% error on the low side
> in the reading!

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

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