I used to think that the rise and fall times of the CW pulse didn't really matter much to the sideband levels; I believed that it was more a function of the waveshaping, especially at the corners of the pulse.
But I just ran a quick simulation of a pulse train going through both a raised cosine and then a sigmoid filter (because those two have been mentioned in this thread) and the rise time definitely does affect the pulse sidebands. The reduction in the sideband levels (what some folks here called 'clicks'... not sure that's a good name for this) varies depending on where you measure it, but in general the sidebands will drop anywhere from 0 to 12 dB-- sometimes less, sometimes more-- when you go from 2 msec to 8 msec rise/fall times. For instance, arbitrarily choosing an offset of 500 Hz from the carrier, the sideband drops by 11 dB for the longer rise time. That turns out to be a fairly typical value. And by the way, in general the sigmoid does a better job than a raised cosine. Arbitrarily defining the occupied bandwidth as the -60 dBc points of the spectrum, and using the sigmoid function with an exponent of -1, the bandwidth of the rise time = 8 msec pulse is 420 Hz versus 640 Hz for the pulse with 2 msec rise time. It's not an enormous difference, but it is something. Anyway, there's another data point for the discussion. R, Al W6LX ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
