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*Subject*: [amsat-bb] Re: SSTV Algorithms?*From*: Curt Nixon <cptcurt@xxxxxxxxx>*Date*: Fri, 17 Oct 2008 08:52:26 -0400

Hi Joe: I beg to differ with you on the sampling information. Having been a digital signal acquisition and instrumentation specialist for a number of years, I'm quite familiar with the nyquist criteria and all. Sampling at 2f, you know the frequency and something about amplitude of the signal and thats about all. That stuff about knowing ALL about it is just not true--"if" you knew ahead of time, that the signal in question was nothing but sinusoidal, then yes, you are correct--but how often is that the case. That is what has driven highly oversampled AD conversion. If you meant twice the maximum frequency COMPONENT of the signal, then thats close, but is still based upon sin theory (fourier series) and leaves alot of detail out of non-sinusoidal parts of the signal unless one considers all of the harmonic content of the source. For investigative or diagnostic work, especially characterizing waveshape leading edges of clocks, etc, we used to recommend sample rates of 5-8 times the highest frequency component of interest. I wasn't so interested in the actual SSTV algorithms as I was in seeing if there is any visible difference in the result of different algorithm use--or is everyone using the same decoding kernel? Thank you Sir, I suspect you know all this anyway--thought I would clarify it as I came to understand it. Curt KU8L Joe Fitzgerald wrote: > Curt Nixon wrote: >> I expect that the faster the soundcard samples, the better? >> >> > It's counterintuitive, but through the magic of sampling theory, once > you sample at twice the maximum frequency of the signal you are > interested in you know _everything_ about it! As a practical matter, > most ham gear audio rolls off sharply above 3 kHz (and SSTV is lower > than that) , so sampling at a measly 8 or 11.025kHz rate is plenty. > Howard Long wrote: >> Do you know of detailed texts that are public domain? If >> so let's have 'em! >> >> > > And it's not public domain, but it is available as free software: > check out QSSTV for source code. > > If you are interested in sampling theory, check out > http://www.dspguide.com/ch3/2.htm > > -Joe KM1P > _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

**Follow-Ups**:**Re: SSTV Algorithms?***From:*Simon \(HB9DRV\)

**References**:**SSTV Algorithms?***From:*Curt Nixon

**Re: SSTV Algorithms?***From:*Joe Fitzgerald

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