[Elecraft] K3 Wattmeter Calibration

[Don Wilhelm]

Roger,

The quick answer is "it does not" - however ---

The default wattmeter calibrations are pretty close to optimum.
Yes, if the wattmeter calibration is done before running the TX gain 
calibration, the results will be better - assuming your external 
wattmeter is accurate.

One item to be considered is that the K3 wattmeter calibration can be no 
better than the accuracy of the external wattmeter.  Many ham grade 
wattmeters are speced at 20% of full scale, so on a 200 watt scale, the 
reading can be off as much as 40 watts at any point on the scale - set 
for 20 watts, the error can be as much as 4 watts, again at any point on 
the scale.  That does not provide sufficient accuracy at 5 watts, nor 
even at 50 watts.

Even the revered Bird wattmeters are good for 5% of the full scale 
reading (right after calibration), so with a 100 watt slug, that is 
still a potential error of 5 watts (at any point on the scale).  How 
many Bird slugs do you have with a recent calibration sticker?

I am referring to analog wattmeters, and although digital wattmeters 
suffer from the same error potential, the error is normally a percentage 
of the reading rather than a percentage of the full scale reading.

End - periodic wattmeter accuracy RANT.

If you are assured that your wattmeter is accurate, then use that 
wattmeter calibration, but if you do not know the accuracy of your 
wattmeter,  you will have to depend on the K3 default calibration.

FYI, I depend on a Telepost LP-100 wattmeter which has been calibrated 
to NIST standards as my "secondary standard" at the workbench.  It is 
guaranteed to 5% of the actual reading, but is typically in the 2 to 3 
percent range.  It is used as a 'sanity check' for my other wattmeters.

73,
Don W3FPR
On 10/30/2013 9:05 PM, Roger D Johnson wrote:
> If you don't calibrate the wattmeter how does the K3 Utility know when 
> the output
> is 5 or 50 watts?
>