[Elecraft] Re: variations in performance of same kits

[David F. Reed]

Jeremy,

think of mechanical tolerance issues for a minute; let's say, a shaft 
and a bearing for example; take 1/4 inch diameter, with some tolerance 
and take the specifications; imagine the diameter specs are .250 inch, 
but to make sure it fits, the hole in the bearing might be specified at 
0.251 +/- .002, and the shaft might be specified at 0.249 +/- .001  so 
as you grab parts out of bins, these tolerances vary, so you could end 
up with bearings ranging from 0.249 to 0.253 inches, and shafts ranging 
in diameter from 0.248 to 0.250; if the parts are from opposite ends of 
variance, they are either loose, or too tight; and some are just right.

Take it to an electrical circuit; the parts have tolerances too, and for 
caps and inductors, the resulting resonant frequencies are different; 
now take the toroids; how evenly the windings are spaced affects it 
somewhat in value.  The transistors will vary in parameters also, having 
slightly different gain and requiring slightly different biasing to get 
that gain.

This is why the circuits have adjustments, such as the trimmer caps and 
resistors; so that you can get these circuits to perform "as designed".  
Imagine now that all of the components have some tolerances, and you can 
see that "plug and play" is not so easy in the analog world, and we end 
up with these variations.

Then there is the measurement issue on top of that; our watt meters have 
the same issues, and calibration issues as well; so we might all be 
using the same watt meter, and if I take my radio to all of us, it will 
measure slightly different output, based on slightly different 
temperature, slightly different impedance of load, slightly different 
supply voltage, and variations in watt meters.

That is where knowing the resolution and accuracy of the test equipment 
come to play.

Probably more than you wanted to know, but there are a lot of variables 
contributing to the variations reported, to say nothing of damaged parts 
and shorts and stuff that throw it all off.

73 de W5SV, Dave

Jeremy Cowgar wrote:

> Why the difference, they are all the same rig why would it change from 
> rig to rig?
>
> Jeremy
> KB8LFA