[Elecraft] K2 keying mod details and circuit theory

[Wayne Burdick]

Hi Ed,

The K2 keying mod involves several parts, and the changes are quite easy to
make. Nearly all of the changes are to the Control board, in the area around U10A.

The complete keying mod document will be posted next week. But here's the
executive summary: The original classic R/C exponential keying envelope is
converted to an optimized sigmoidal (S-shaped) envelope. This is done by
reconfiguring U10A as a 2-pole filer whose step response has the desired
rise/fall characteristics. But we were also careful to not make the rise and
fall times too long, which could result in "soft" keying. (We plan to write an
application note for those who want to custom-tailor the rise and fall times,
putting them somewhere in between the original and new values. Only one or two
component will need to be changed to achieve this.)

Other transceivers have been modified by third parties along these same lines.
But since so many of our customers are CW operators, we felt that we should
upgrade the K2 rather than leave individuals to fend for themselves. The K2 will
now be in the top tier of transceivers in terms of CW bandwidth.

About a dozen K2 owners field-tested the changes and reported nearly identical
results. One measured about a four-fold decrease in occupied bandwidth. We'll be
posting our own before/after spectral plots, too. 

73,
Wayne
N6KR



Eddy Avila wrote:
> 
> Can someone describe what the new keying mod kit from Elecraft is and how
> many components one has to replace to make the mod??
> 
> I know the website says you must also upgrade the firmware in order for the
> keying mod to work.
> 
> Thanks and 73....ed
-- 

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