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List:       elecraft
Subject:    Re: [Elecraft] K3: LPA power level accuracy?
From:       James Sarte <k2qi.nyc () gmail ! com>
Date:       2010-10-30 1:19:36
Message-ID: AANLkTinG1iJj=Z-uOsM2Rr=z32zew=dywztoMw7+sE8Z () mail ! gmail ! com
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Hi Don,

My Bird analog meter and MFJ-828 digital meter were previously calibrated by
a friend and colleague with the proper tools.  According to him, both should
have had a margin of error of about 5-7%. - perhaps 10% now given the time
that has elapsed.  Regardless how accurate his claim was, I can't be sure -
so I take what he's stated at face value.

Anyway, you're absolutely correct in stating that there are too many
variables at play.  With my poor ground plane, even rain water saturating
the balcony has an affect on SWR and forward power.  I suppose I should be
satisfied that at least my LPA output measurements fall within a 10% bracket
of error.  I was simply curious if others have experienced similar when
using the LPA.

73 de James K2QI

On Fri, Oct 29, 2010 at 8:10 PM, Don Wilhelm <w3fpr@embarqmail.com> wrote:

>  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
>
>
>
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