|Subject:||Re: LF: Key Clicks|
|From:||Rik Strobbe <[email protected]>|
|Date:||Wed, 25 Aug 2004 12:28:57 +0200|
|References:||<[email protected]> <[email protected]>|
Just look at CW signal as an AM signal.
Assume you have very hard edged "on / off" keying and key an long series of dots at a speed of 12 WPM :
12 WPM = 600 dotlengths per minute (according to the "PARIS" system 1 word = 50 dotlengths), so in fact you modulate an AM TX with a 5 Hz rectangular "audi signal".
The spectrum of this signal will be a carrier with a whole bunch of sidebands in 5 Hz intervals from the carrier. The first sidebands (carrier +/- 5Hz) is useful all the other (higher) sidebands are waste (wasted power + useless bandwidth) and and show up as keyclicks.
As the keying gets softer (longer rise- and falltime of the keying) the higher sideband will become weaker (less keyclicks). In order to have no higher sidebands at all you would have to get modulation (= keying) sinusoidal. In that case the modulation signal has no harmonics and thus keying will be clickless.
So far the theory, because the above assumes a long (a la limite endless) series of dots.
Our real-world CW instead is a rather random sequence of dots and dashes. But regardless how you do the keying the worst condition (largest bandwidth) is a series of dots. This means that the "useful bandwidth" of a CW signal is determined by speed and the maximum "audio component" of the keying can be determined as :
Fmax = WPM/2.4 where Fmax = the highest useful "audio frequency" (in Hz) and WPM = keying speed (in words per minute)So the ultimate way to get a clean CW signal is to filter they keying signal through a good LPF at Fmax.
But in most cases a simple RC filter will give the best "effort vs. result" ratio.
73, Rik ON7YD
At 10:32 25/08/2004 +0100, you wrote:
Good morning all,
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