Posted by
Don Wilhelm-4 on
Oct 30, 2010; 12:10am
URL: http://elecraft.85.s1.nabble.com/K3-LPA-power-level-accuracy-tp5688027p5688424.html
James,
There are too many variables to give you a good answer.
Are you using the lowest scale on your wattmeter? Is the difference
between the K3 power setting and your wattmeter reading less than 10% of
the wattmeter's full scale reading? If so, you can likely blame the
difference on your wattmeter at low power levels.
You can calibrate the K3 internal wattmeter - at both the 5 watt and the
50 watt points. The procedure is in the Calibration section of the
manual. However, I would strongly suggest obtaining a measurement tool
that is better than the typical analog wattmeter. A calibrated Telepost
LP-100 wattmeter is one solution, a calibrated Elecraft W2 is another
good solution, and an inexpensive solution that will work well for the 5
watt calibration is the Elecraft DL1 with its built-in diode detector.
The latter solution will be quite accurate if you read the voltage with
your DMM and compute the power as indicated in the DL1 manual.
Accurate low power measurement (error less than 5%) is not an easy task
- it ranks right up there with making MDS measurements.
You may look in the archives to see my occasional "rant" about wattmeter
accuracy.
73,
Don W3FPR
On 10/29/2010 5:00 PM, James Sarte wrote:
> Hello fellow Elecrafters,
>
> Quick question - I've noticed that when using the LPA, output power is
> always slightly off compared to the reading given off by two fairly accurate
> meters. For example, a constant carrier output of 5 watts always reads
> about a half-watt less on the external meters. The output power from the
> KPA3 however has always been on the dot - 80 watts drive reads 80 on the
> meter, 100 watts output reads 100W on the meter, etc. etc.
>
> I'm not really concerned, but was wondering if this was typical? I've
> calibrated several times in the past using the K3 utility, but the results
> are usually the same.
>
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