Kevin, AC0H, wrote:
How do the rise and fall times of the SSB and CW waveforms compare? Isn't SSB, even with VOX delay turned all the way down, a lot slower than CW? If the SSB rise and fall times are slower than CW how do you get clicks? I would agree that nobody in their right mind would cut loose with 800wpm HSCW on the HF bands becasue of the bandwidth used. I can't remember the old formula for figuring the bandwidth for CW signals of any arbitary speed. ------------------------------------ With proper waveform shaping, the CW bandwidth in Hz that is required is approximately 4 times the speed in WPM. So a 20 wpm signal needs about 80 Hz to pass the on/off transitions without stretching them out and impairing the readability. SSB allows 2.5 kHz or more bandwidth which would support about 800 wpm. That is, of course, way too much for the CW bands. As others have pointed out, that takes being careful about the nature of the driving signal, possible noise introduced by the oscillator-rig connection, and a clean audio waveform, as well as proper keying waveform. A number of SSB rigs used that technique to produce CW in years past. Some early SSB transceivers had no ready means to key the RF source, so they provided a keyable sidetone oscillator that also fed the TX chain. As a brass pounder 99% of the time, I didn't follow the transition from audio-injection to keyed RF sources in the newer transceivers, but I suspect it had to do with the issues of keeping the signal clean with adequate sideband and carrier suppression. Current rules require such spurious emissions to be at least 40 dB below the peak carrier for transmitter > 5 watts (with a 50 mW limit no matter the power) or at least 30 dB down for a QRP transmitter (up to 5 watts). Elecraft spec's the carrier suppression at -40 dB (typical) for a K2 with the SSB adapter. I suspect that's very conservative, and allows for some sloppiness in setting the carrier null. Still, I'd check the actual level from my K2 if I tried that scheme running QRO. The opposite sideband rejection should be no concern considering the K2 OPT1 filter characteristics. I would not expect the VOX to be at all useful in such CW. Actually, a lot of the HSCW is done like we used to do ALL CW just a few years ago: no QSK! For scatter work, one doesn't know what one received for a period of time anyway. It has to be played back slowly while the op tries to hear the fragments of CW in all the noise. It's about as far from QSK as one can get. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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