It's basic physics, Jim. A keyed signal is amplitude modulated and an
amplitude modulated signal produces sidebands. 

Your are quite right that the rise time affects the amount of spectrum the
sidebands make. Of course, higher keying speeds require faster rise and fall
times, otherwise one code element would begin before the fall time allowed
the previous element to stop. 

Indeed, the way to reduce clicks is to extend the rise and fall times. The
slower the rise and fall the less "click" energy around the carrier. In the
extreme you make the rise and fall times infinite (that is, you don't key
the carrier at all). Then you'll have no sidebands (clicks) at all. 

If you modulated the signal 100% with a pure sine wave, you'd only have two
sidebands at discrete frequencies above and below the carrier separated by
the frequency of the modulating signal. The issue with CW is that we don't
use a sine wave. No matter how we look at it, we distort the keying signal
by stopping it at the point the carrier is full on during the rise and full
off at the fall. That distortion produces further sideband energy beyond the
sideband produced by the keying waveform. 

Advanced shaping techniques such as those used in the K3 minimize that
energy in the sidebands, but it's still there.

Poorly designed and operated rigs can produce keying sidebands far in excess
of what's needed for good communications, just as poorly designed and
operated AM or SSB rigs produce sidebands far in excess of what's needed. It
sounds like you've run into one of those. I think anyone who spends enough
time on the CW bands will find them. They come from two sources.

One is the design of the rig itself. You are quite right that some rigs are
better than others. Considering that just about any transmitter built since
the demise of spark in the 1920's is perfectly legal on our bands today,
sometimes it's a limitation of the design. Among current designs, some are
better than others.  

The other is operator error. In these days of mostly factory-designed and
built rigs, it's usually caused by over-driving an amplifier in the mistaken
belief that linearity isn't important in CW. Linearity is very important to
retain the keying waveform of the rig driving the amplifier, just as it's
very important to preserve the waveform of an SSB signal. It's also why it's
bad practice to turn the POWER knob on a K3 or K2 full clockwise, even on
CW. IMD (distortion) increases as you go past the rated 100 watts output. On
CW distortion is heard as clicks as Jim notes. 

Indeed, for over half a century that I know of, we've always defined
"clicks" as excessive CW sidebands, recognizing that normal sidebands are
always present. Until fairly recently, it was not possible to listen to the
sidebands in a CW signal using a typical communications receiver without
hearing the carrier too. They were just too close together. Nowadays our
advanced receivers can split the sideband off of the keyed signal, just as
for years we've been able to split the sidebands off of an AM signal. 

On CW those sidebands sound like clicks. 

Ron AC7AC



-----Original Message----- 

And I strongly DISAGREE with Ron's statement that clicks are an essential 
part of CW. Clicks are a function of a FAST RISE TIME and DISTORTION, not 
keying speed. There's a KH6 contester who moved from K4 with a monster 
signal, monster clicks, monster SSB splatter, and monster attitude to go 
with it. I've told him about his clicks and splatter several times,  but 
the clicks, splatter, and attitude are still there. 

73,

Jim K9YC


______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Reply via email to