[Elecraft] KPA1500 Linearity

[Bob McGraw K4TAX]

Yes and most power meters are voltage sensing instruments which are 
calibrated to a specific value or load.  Thus is the load being used may 
not be the identical value to which it was calibrated, hence another 
error enters the equation.

To wit, I have 3 "allegedly" 50 ohm dummy loads.  Only one is actually 
50 ohms but others are as low as 45 ohms and as high as 58 ohms, while 
one actually measures 50.5 ohms.   If one is trying to measure power 
then both voltage and current should be measured with a known load and 
then do the math.  If you are using an antenna, it most likely is 
somewhat reactive.  This throws another curve into the ballpark in terms 
of power measurement.

73

Bob, K4TAX


On 6/19/2018 7:15 PM, Fred Jensen wrote:
> Most, if not all analog measurement devices are spec'd at % of full 
> scale which can lead to high absolute variances if the levels being 
> measured are significantly below full scale.  A Bird with a 100W slug 
> accurate to 10% of full scale [+/- 5W] would be within spec if it 
> indicated a real 10 W signal at 5 W.  Many folks would say, "My K2/10 
> will only produce half the power it should."  Most digital 
> measurements involve processing circuitry/computation, again which can 
> introduce errors in the lower end of a range, and be dependent on 
> frequency as well.
>
> Mathematics can be hard.  Arithmetic can be tricky. [:-)
>
> 73,
>
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County