[Elecraft] [K3] SWR - Numerical Indication

[Don Wilhelm]

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.