[Elecraft] High Accuracy Wattmeter

[George, W5YR]

Charles, get in touch with Steve Weber - "melt solder" - and look into his
digital power meter. You are only looking for 5% accuracy in the worst case
- 0.05 watts out of 1 watt = 5% of 1 watt - so I would not think that would
be a severe problem. That is, if we both mean the same things with
accuracy, precision and resolution.

Steve's meter reads out to four significant figures in the LED display and
has a built in "precision" 50 ohm/10watt load. He claims +/- 3% accuracy
with one milliwatt resolution on the readout. I am not sure how to equate
that with your requirement for "0.05 watt precision over the entire scale." 

At 10 watts, his LSD represents 10 mw which is 5 times better than the 50
mw you are seeking. The three percent accuracy spec suggests that the
reading will be correct to within +/- 300 mw at 10 watts which could be as
much as six times worse that your 50 mw requirement. Or, it could be right
on the button . . .

72/73/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
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Charles Greene wrote:
> 
> Hi All,
> 
> I need a high accuracy wattmeter for reading power from 1 to 10 watts into
> a 50 ohm load with a precision of 0.05 watts or less over the entire
> scale.  I tried a RF probe and a DVM, but the voltage is all over the
> place.  I have a scope, but reading that is like reading a meter.  If I set
> the K2 control, it drifts up pretty much.  Anyone know of any circuits off
> hand that will do this?  How about a DVM connected to my OHR WM1?  I can
> accurately calibrate the voltage reading using a service instrument, but I
> can't use that for the power reading unless the power is going to the
> instrument which it isn't.