On Oct 5, 2010, at 12:36 AM, David Woolley (E.L) wrote: > The Shannon formula, and in particular the error free condition, is only > valid for gaussian noise.
Yes, the main Shannon Theorem (Theorem 17) mentions "thermal" noise. (In addition to being Gaussian, Theorem 17 also requires that the noise be white.) However, check out Theorem 18 in the same paper. It establishes upper and lower bounds for the Channel Capacity for non-Gaussian and non-white noise. > 56kbps modems don't rely on source coding, except, possibly, in as much as > all modems, other than FSK ones, require scrambling. FSK is of course just a modulation scheme, so it makes no sense to talk about FSK source coding. But if you consider Baudot RTTY, which is FSK+Baudot, then yes, Baudot RTTY does rely on source coding to maximize the number of characters per bit as long as you don't switch often between text and punctuations/numbers. As far as scrambling/interleaving goes (at least with their presence in systems such as MFSK16 and SITOR-B), I prefer to think of them as a form of channel coding (whose primary objective is to minimize channel errors) instead of a form of source coding (whose primary objective is to reduce the average bit rate of data that is sent to the channel coder). 73 Chen, W7AY ______________________________________________________________ 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
