While the impact on a receiver might cause "clicks" to be heard, that's a failing of the receiver, not the transmitter.
The real issue about the CW keying waveform is the production of sidebands around the CW signal at the transmitter. All amplitude-modulated signals, which CW is one type, have sidebands. The only way to prevent them entirely is to not modulate the signal. Since the rate of the modulation is much less with CW than it is with a spectrum of voice covering, say, 300 to 3000 Hz, the sidebands produced by CW keying are much, much smaller than those produced by voice modulation. But that doesn't mean the sidebands produced by CW keying can be ignored, especially in today's world of very selective receivers that allow signals to be much closer to each other than in the past. Without the sidebands, the CW would be unreadable. It's a question of how wide the sidebands must be and how the energy is distributed in them to produce an easy-to-copy signal that is not wider than necessary. "Easy-to-copy" is a value judgment. There are no absolute values. Exotic computer-controlled keying circuits with linear RF amplifiers have given designers the ability to control the keying waveform and the energy distribution in the sidebands to a degree never contemplated only a few years ago. But the underlying question is unchanged: what is the best tradeoff between bandwidth and readability of a CW signal? It's still a judgment call. Ron AC7AC -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Monday, March 31, 2008 9:16 PM To: [EMAIL PROTECTED]; elecraft@mailman.qth.net Subject: Re: [Elecraft] CW rise time mod It's not that 3ms is a lot of time in terms of human scale. But, it is the rise time of an electronic pulse. This can have a lot of impact on the transient waveform that results in an audio demodulator - i.e. receiver. The difference is noticeable enough to make the difference in a crowded band weak signal situation when the receiving station is differentiating what he hears. That's why a banjo sounds different than a guitar or violin. Al WA6VNN ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + In a message dated 3/29/2008 5:34:22 P.M. Pacific Daylight Time, [EMAIL PROTECTED] writes: People, 8 ms.- 5 ms.= 3 ms., does it matter in any practical sense? I would really like to know who cares, and why? Can anyone hear the difference? Three-thousanths of a second? Not my old brain. 73, John, W2GW K3 #384 ----- Original Message ----- From: "Lyle Johnson" <[EMAIL PROTECTED]> To: "Elecraft Reflector" <elecraft@mailman.qth.net> Sent: Saturday, March 29, 2008 5:21 PM Subject: Re: [Elecraft] CW rise time mod >> Or do Rev A RF boards have a lower value for C222 than that shown on >> the >> schematic? > > Early production K3 RF boards have a 1 uF capacitor instead of a 0.1 > uF > capacitor installed at C222. Yes, the published schematics show a 0.1 uF > capacitor. The effect of the larger capacitor is to increase the TX > waveform rise time to about 8 ms instead of 5 ms. > > Rev B RF boards have the correct 0.1 uF value installed. Sometime > during > Rev A RF board production, the value installed on the board was changed > from 1 uF to 0.1 uF. > > Surface mount ceramic capacitors are not marked with a value, so you > cannot tell which you have by visual inspection. > > You can determine if you have a 1 uF rather than a 0.1 uF by: > > 1) Measuring the capacitance if you have a capacitance meter. > > 2) Looking at the Tx output RF envelope on an oscilloscope or > "station > monitor" scope. If the fall time and the rise time look very similar in > duration, you have the 0.1 uF cap. If the rise time is about 50% longer > than the fall time, you have the 1 uF capacitor. You don't need an > oscilloscope with an accurate time base to make this comparative > measurement. If your oscilloscope has a low bandwidth (2 to 10 MHz), use > the 160 meter band. > > 3) If you are concerned that your unit may have the 1 uF capacitor > and you > have no way to determine it otherwise, you can just replace it with the > 0.1 uF part and sleep better at night :-) > > If you don't change it, you will not damage anything. Your K3 will > just > have slightly softer keying and an upcoming firmware adjustment of the > keying time will be less accurate. > > 73, > > Lyle KK7P > > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com **************Create a Home Theater Like the Pros. Watch the video on AOL Home. (http://home.aol.com/diy/home-improvement-eric-stromer?video=15&ncid=aolhom0 0030000000001) _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
