http://elecraft.85.s1.nabble.com/Power-Measurement-tp395167p395169.html
> You can also fine tune the formula based on DC measurement of the
> resistance of the bottom half of the load. The formula assumes an
> exact 25.0 ohms for the bottom half of the load.
>
> Also, measure the resistance at the temperature you will be using for
> testing. You can see a graph from my HP VNA at
> www.telepostinc.com/loads.html for both the DL-1 and a Caddock MP930
> thick film resistor mounted on a heat sink. The DL-1 shows some
> variation with temp... about 0.5 ohm from room temp to 1 min key down
> at 10W. The Caddock showed less, but I seem to have misplaced the
> graph for it.
>
> If you take these and Don's caveats into account, the results should
> be pretty good, especially near the high power limit of the load where
> the diode drop becomes a less significant factor.
>
> Larry N8LP
>
>
>
> Don Wilhelm wrote:
>> 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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