[Elecraft] K2 crystal matching and SSB

[Wayne Burdick]

Glenn Maclean wrote:

> I am not sure when Elecraft went to the matched crystals for the K2.


Glenn (and others),

We have always matched the crystals in the K2 very closely (to within 10
Hz or better). We use a very sensitive, precisely loaded test fixture to
match based on the crystal's series-resonant frequency. So matching has
nothing to do with Phil's or anyone else's SSB signal characteristics. 

However, a small percentage of crystals supplied by the manufacturer did
have higher than average motional inductance (Lm), and thus produced
somewhat narrower filter passbands. There's no way to identify these
crystals from the rig's serial number since crystals are first matched,
then placed into our inventory to be used at a later time. But the small
number of higher-Lm crystal sets were probably used up a long time ago. 

We now use only crystals that have been pre-screened for a specific
range of motional inductance by the manufacturer. Nearly all crystal
sets that we had shipped already fell into this range, but the screening
step guarantees that all K2 builders will get consistent results.

Anyone who suspects they might have an SSB TX passband that is too
narrow should e-mail gary@elecraft.com. Gary will tell you how to check
your filter crystals using a simple test. Elecraft will replace any
crystal sets found to be too narrow. 

Note: The KSB2's nominal bandwidth is 2.2 kHz, with the acceptable range
being anything from about 2.0-2.4 kHz. Our goal was to give the K2
"punchy" audio, not "hi-Fi" audio, and this strategy has been proven
effective in on-air tests. Still, some operators have experimented with
wider filters. In particular, see John Grebenkemper's recently-posted
application note. John lists alternate capacitor values for the KSB2 for
various bandwidths. 

73,
Wayne
N6KR