Re: Power meter accuracy

dekle <dekle@...>


Hi Bruce,

The accuracy specification in the WM-1 manual states that the accuracy is "5% of full scale and 8% worst case". (Makes you wonder why they just don't just say 8 % ???)

So on the 20 w scale that is +/- 1 watt (using the 5% accuracy figure).

So, if you read 3 watts on the WM-1, it could still be within specification for an actual power anywhere between 2 to 4 watts.

I read their manual and it has some really interesting stuff in it and there is a big discussion of accuracy. If I use a power meter, I just use it for relative readings.

Oscilloscopes are getting pretty cheap now. If I want more accuracy, I like to look at the waveform across a dummy load and do the math to calculate the power.

Finally, if the power indicator on the Argo is exactly between '3' and '5', that may not be '4' due to the non-linearity of the meter. Plus, the Argo wattmeter also has an accuracy tolerance, I'm sure.

You can't win.








"I did a bit of "domestic archaeology" in the attic this afternoon and
found a long-forgotten Autek Research WM1 SWR/PWR meter. Managed to even
find the matching wall-wart !! Put it in-line with the TenTec Argo 556
and noted a difference in power reading between the Argo and WM1. The
meter in the Argo shows 4 watts (dead center between the "3" and "5"
points on the front panel meter) and the WM1 shows exactly 3 watts on
the 0-20 scale.

So, which one is closer to the truth? In the big picture, it doesn't
really matter but I'm enough of a radio nerd to want to know closer than
"3-4 watts". Is there a way to determine which reading is accurate? Can
the WM1 meter cause that much power "loss"? I do not have any test
equipment here so it may be a moot point. Your comments welcome. Thanks
in advance."

Bruce AA5CO
4SQRP #664
SKCC #10643T

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