[Elecraft] K3 Watt Meter Calibration Question

[brian]

Don,

Can't argue with this.  A long time ago a wise engineer said: "Never 
believe the last digit displayed".  He was talking about the newly 
released 3 and 4 digit equipment display. Today it's almost as you say. 
  Believe the first two.

There are some exceptions to this rule.  HP equipment (at least the 
older stuff) would only digitally display the number of truly believable 
significant digits.  For example, their counters would not display all 
available digits but just those one can real.  So there are exceptions 
to all rules of thumb.

One has to know their measuring gear characteristics to know what to 
believe.

73 de Brian/K3KO



On 6/6/2016 0:37 AM, Don Wilhelm wrote:
> Clark,
>
> The detection diodes in the K3 (and the LP100A wattmeter as well), do
> not have a perfectly linear relationship vs. frequency response.
> The LP-100A is quite good, but can be in error by as much as 5% (Larry
> will not guarantee it closer, I have asked).
> The K3 wattmeter can also have up to a 10% error in its readings (may
> vary with frequency).
>
> So the net of what I am trying to say is that at the 100 watt level, a
> wattmeter reading between 90 and 110 watts is within the range of normal
> expectations.
>
> We have come to be "accuracy obsessed" since the advent of digital
> displays.   In the days of analog meters, there was always a region of
> uncertainty due to the inability to read the needle on the meter to a
> high degree of accuracy - parallax effects, the width of the needle, as
> well as the inherent accuracy of the circuits the meter was indicating.
> In todays world of digital displays, we assume that all displayed digits
> are true and accurate, when in truth, only the first two digits of the
> display are valid in an instrument that measures to a 10% accuracy.
>
> 73,
> Don W3FPR
>
> On 6/5/2016 6:49 PM, engineercm wrote:
>> Noticed today 20m output measured by LP100A was 90w when K3 wattmeter
>> set to
>> 100w. Same with 10m; other bands measured close enough.  Updated
>> firmware to
>> latest and performed Transmit Calibration.  Calib:WM HP at 50w set to
>> agree
>> with LP100A.  In order to get 100w on LP100A, I have to crank the K3
>> output
>> so that it reads 110 on the internal wattmeter.  Why?  Slope effect of
>> internal WM?
>>
>>
>
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