[Elecraft] [K3] SWR - Numerical Indication

[Dave Hachadorian]

This discussion reminds me of a lesson in engineering class (55 
years ago) about the difference between precision and accuracy. 
The professor used the example of bullet holes in a target.

If the holes were closely spaced, but far from the bulls-eye, the 
shooter was inaccurate but precise.

If the holes were widely spaced, but the average was near the 
bulls-eye the shooter was accurate but imprecise.

Closely spaced on the bulls-eye precise and accurate

Widely spaced, and the average not near the bulls-eye, imprecise 
and inaccurate.

Easy to remember.

Some other memorable nuggets from that class:
Evaporation is a cooling process.
High octane gasoline is slow-burning gasoline.
The electric company bills you for kilowatt-hours, so they are 
not a power company, they are an energy company.


Dave Hachadorian, K6LL
Yuma, AZ


-----Original Message----- 
From: Don Wilhelm
Sent: Friday, November 30, 2018 7:55 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] [K3] SWR - Numerical Indication

Petr and all,

Those digital instruments that show 2, 3, or 4 decimal places 
have given
us a false sense of accuracy.
For instance an instrument that is accurate to 5% and has a 4 
digit
display can show us (when measuring a 5 volt source) anywhere 
between
4.750 volts and 5.250 volts and still be within the 5% accuracy 
window
for the instrument.

Review the specs and calibration for whatever meter you are using 
and do
not expect those extra digits to be correct - in other words 
round the
numbers displayed.

Many wattmeters are only accurate to 20% of the reading - so if 
one
wattmeter at 100 watts shows 120 watts and another shows 80 
watts, the
actual power could be 100 watts.  Take that into consideration.

The Telepost LP-100 when calibrated to NIST standards is accurate 
to 5%
(it can be lower, but Larry will not guarantee it).  So any power 
it
displays between 95 and 105 watts can actually be 100 watts.

In other words, look at the specified accuracy of whatever meter 
you are
using and take that into consideration.  Those extra digits on 
your
meter may be meaningless.

73,
Don W3FPR

On 11/30/2018 9:29 AM, Petr, OK1RP/M0SIS wrote:
> Hi Wes,
>
> excellent!
>
> Many thanks for this post which is nicely explaining what is 
> going on about
> the measurement in K3s.
>
> In fact until now no one talked about the calibrations, 
> uncertainties,
> errors, accuracy, reading errors, uncertainties A, B and 
> combined
> uncertainties etc. In that case there is several error sources 
> and factors
> which need to be calculated in order to get some more precise 
> values ...and
> in all cases the uncertainties must be calculated together with 
> measured
> value if we would like to talk about scientific or 
> sophisticated
> measurement.
>
> Thanks for nice explanation Wes to all.
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