RE: Power Measurement

Posted by Don Wilhelm-3 on Nov 07, 2006; 7:55pm
URL: http://elecraft.85.s1.nabble.com/Power-Measurement-tp395167p395168.html

Ed,

Yes, the formula in the DL1 manual is off a bit - there was some discussion
about that on the reflector about 6 months ago.

As I calculate, the correct formula is P(watts)=(1.414(V(volts)+0.15))^2/50
Or easier expressed as P=2(V+0.15)^2/50 (I am not certain why the square
root of 2 (1.414) appeared inside the term to be squared - much easier just
to square it and move it outside).

The diode drop must be added to the voltage read on the DMM for low power
measurements.
If you wish better accuracy, measure the actual forward voltage drop across
your particular diode, they will vary a bit from diode to diode.  Use the
measured value in place of the 0.15 factor in the formulas above.

73,
Don W3FPR

> -----Original Message-----
>
> The formula given in my DL1 manual is not correct, in my view.
> The lower the
> power, the more incorrect it becomes.
>
>
>
> Ed Lambert KD3Y
>

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