[TenTec] CW Key Clicks and Filters

[Jim Reid]

Hi,

Spent a few hours during the CQ CW DX test.  I was
particularly interested in finding pairs of close signals: one
very strong, other quite weak.  Of course I found many such.

However,  many of the close in "weak" ones could not be
copied,  even cranking in much DSP filtering of  the RX-340.
Why?  Strong key clicks from the  "near by" strong signal.

About 70% of the S9 and stronger signals (none more that
15 dB over 9 as heard here in KH6 land) were generating
various "bandspreads" of clicks.  ALL of the strong signals
which were operating at 37 wpm or faster were generating
harmful clicks to nearby weak signals.  

One theory suggests that the wide click bandwidths (generated by
very steep rise time CW waveforms) were "generated" on-purpose.
That is, to clear spectrum space!  My theory is:  the operators were
unaware of what was going on.  Some rigs just do this because
of their design (FT-1000D and MP's are so reported,  see for example:
http://lists.contesting.com/_yaesu/1997-December/001420.html ;
or even linear amp problems at high speed,  see for other info:
http://www.amrad.org/pipermail/lf/2000q2/000433.html ;
unfortunately the site by W8JI is still down,  as it has
much info about eliminating key clicks).

I wonder if ALL rigs "click" at higher character speed,  maybe
only do so when the CW character speed is pushed  high,  that
is well over 35wpm.  I found very few operators going much over
38 to 40 wpm on the weekend,  but there were a few,  and every
one "clicked" over several hundred Hz on each side of the carrier.

These clicks are essentially not noticed unless you are listening
with 500 Hz or narrower bandwidth;  and very easy to hear when
tuning slowly up or down the band with 300Hz or more narrow DSP
bandwidths.  That is the way to find the weak,  far away stations:
slow tuning,  maybe in only 10Hz steps and using 150 or so Hz
bandwidth.  But this technique really goes "to pot"  when a strong
click generator is near by!

I very much anticipate my coming Orion in which I can tailor
the CW waveform;  I will not use a steep rise or fall time!
The Orion,  with proper use,  will not be a generator of these
harmful clicks!

Just thoughts I have following the past weekend.

73,  Jim  KH7M