[Elecraft] K3 Watt Meter Calibration Question

[Clark Macaulay]

Hi, Don.

I suspected as much.  Precision (number of digits) and accuracy (compared
to a known standard) are very different. I guess it doesn't matter what the
power level is except when running QRP where one must be below 5w. That's
why I always adjust my power output to be 4.5 w just to be sure.

I'm sure you remember slide rules used in engineering schools before the
pocket calculators came along in the 60's.  I still have mine and when I
look at remember some of my colleagues that would read to 5 digits from
their "slip-stick".

BTW:  it was amazing to watch the K3 run through it's TX Calibration.
After having the K3 for a few years, I'm still learning.  What an amazing
feat of engineering.

Clark
WU4B

On Sun, Jun 5, 2016 at 8:37 PM, Don Wilhelm <donwilh at embarqmail.com> 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?
>>
>>
>>
>


-- 
72,

Clark WU4B
QRPARCI #10815
SKCC #3892
Southeastern DX Club <http://www.sedxc.org>
North Georgia QRP Club <http://www.nogaqrp.org>
Kennehoochee Amateur Radio Club <http://www.w4bti.org>


*"It is vain to do with more what can be done with less."*
*Attributed to *William of Occam (1288 AD - 1348 AD)