[Elecraft] Matched Crystals worth the effort!!!

[Allen C. Ward]

Today I finished installing, re-caling and testing 14 new
matched crystals.  My K2 is serial #1107, so not a field
test or real early unit, but still about two years old.  I had
previously done the mods (KI6WX etc.) to flatten response but I still wasn't
happy with the filter response.
The original crystals were marked 4.91-0195 for the
standard filter and 4.91-20 for the K2SSB.  I also opted
for the toroidal L33 BFO choke.  I first recorded (using
Spectrograph) the original responses and then replaced
the CW filter crystals grounding them low on the can sides.  I then recaled
the BFO settings and recorded the
results.  Now the beat note does not change when selecting different
bandwidths and the response stays the
same or increases slightly as bandwidth is decreased.  This is a GREAT
improvement!  I then changed the K2SSB crystals.  The improvement was not
nearly as
great.  After testing I then did the BFO mod (C174 and
L33 replaced).  I then had to recal the BFO for all filter
modes and bandwidth.  I have a new receiver!!  The
SSB response is almost identical for LSB and USB and
instead of looking like a hock shop western saddle, the
response is very flat from 500 to 2000 Hertz.  Tuned
to a CW signal the frequency readout change from SSB to CW is 600 Hz (the
sidetone frequency).  Sideband
sounds more natural.
This change and the other mods mentioned in the Elecraft
webpage are easy to do and are worth the minimal cost
and effort if you need them.
Allen KA5N


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