QST Review of KAT100 and KDSP2 in Jan 2005 Issue

[Henry Gardiner]

   In this review, the captions to the response curves say that they are
for the DSP.  Inspection shows that they actually reflect the combined
response of the crystal filters and the DSP.  So the uninitiated would
conclude that the pass band response of the DSP is really that bad whereas
the crystal filters are the cause.
   We see here the best example yet of why one should use one of the
spectrum indication programs to set the crystal filters.  In my K2 #4017,
modest changes to the widest crystal filter bandwidths alter the height of
some of the rogue response peaks and valleys.  Such adjustments can be used
to correct much of the imperfection.  I was able to get crystal filter
responses that were considerably flatter than that in the QST review.
   The SSB option board has its own crystal filter network and it provides
a significant additional improvement in flatness at my widest filter
setting.  So I use the SSB option filter for my widest CW filter.
   In the case of these widest crystal filter settings, the entire response
curve can be shoved up or down in frequency to put one of the filter
response peaks at the desired center frequency.  That would be the
operator-selected spot oscillator frequency and the center frequency for
the DSP.
   The narrower crystal filter settings tend to coalesce their peaks and
don't present the same problem.
   I let the K2 warm up completely with the cover on before doing these
adjustments.
   Usually the filter pass band responses of my DSP are exactly that
expected.  I can't corroborate the complaints of harsh audio.  The skirts
of the DSP are much sharper than those of the crystal filters, and the
ultimate rejection is indicated by Spectrogram to be much better.  I was
using the soft curve settings.  Where this really helps me is during
thunderstorms.  These are high-power generators of overwhelming wide-band
noise.
   Of course, in typical operation both the crystal and DSP filters are
used simultaneously.
   During normal operation, selecting the DSP pass band filters is no more
difficult than selecting the XTAL filters.  For me, the infrequent changes
to the DSP filter pass band widths and center frequencies is a puzzlement
and involves referring to the worthwhile "The Nifty Mini-Manual - Elecraft
K2 Plus Options" found at www.niftyaccessories.com, though the Elecraft
manual does OK too.  Really, I should just write down the procedure that I
need in my own words.  I'll do that next time.

   I recommend that Elecraft upgrade the filter setting discussion in the
manual over what's shown for #4017's manual to discuss crystal filter
optimization.  The use of a spectrum analysis program should be made
mandatory.  These changes would benefit the average K2 user and would
provide a more appropriate performance basis for magazine reviews.


73s, Henry AC5LA
   

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