40 wpm has a 3 dB bandwidth of somewhere between 200 and 300 Hz. So,
some 'key clicks' will be noted within a 500 Hz bandwidth due to filter
shape factors [bandwidth at -60 dB] in the receiving radio. Another
source of false 'key clicks' is the third order intercept in the
receiving radio. Strong nearby signals cause the receiver to desense
slightly. This modulates the AGC in the receiving radio. If the
offending signal causes key clicks at S9+15 but not at S7 then the key
clicks are being generated in the receiving radio. If the offending
signal has key clicks at S9+15 and also at S2 then the keyclicks are
from the transmitter.
True key clicks are caused by excessively fast rise and fall times of
the keyed signal. They are not caused by the power level of the radio or
the amplifier.
Without a scope and a spectrum analyzer it is virtually impossible to
truly say a signal has 'key clicks' even though you or I may hear key
clicks in our radio!!
Deacon Dave, W1MCE
Jim Reid wrote:
>
> 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
>
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