[Elecraft] How and Why for matched crystals?

[Don Wilhelm]

John,

Even in the same manufacturing batch, some things will vary within limits
(defined by the 'tightness' of the process).

The crystals for example are typically speced for frequency at +/- 30 ppm,
so at the 4913 kHz K2 IF frequency the variation could be as far apart as
254 Hz and still be in spec.  I would expect the variation from the same
batch to be something less than +/- 100 Hz, but even that is just not close
enough for a crystal filter, so Elecraft sorts the crystals into batches -
if my memory is correct, that sorting is done to 10 Hz or less.  Even if my
numbers are in error, a random set of crystals just will not make a good
crystal filter due to the frequency variation.

Similar with transistors, the gain of the transistors will vary - usually
not a problem until you use 2 of them in a circuit sharing the same base
bias, and then the one with higher gain will conduct more throwing a
'balanced' circuit into a slightly out of balance state.  If one tries to
get max power out when these conditions exist, the higher gain transistor
may go into saturation or even destroy itself.

73,
Don W3FPR

----- Original Message ----- 

Out of pure curiosity what does Elecraft mean by matched crystals and
matched transistors?  That they came off the assembly line from a same lot
or that they were somehow tested till they found similiar ones?  How is it
better than unmatched pairs?