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4298Re: [wsjtgroup] Optimization of MS Fresnel zones vs. bit rate & error correction?

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  • Joe Taylor
    Feb 1, 2008
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      Hi Ross and all,

      Ross (N0GSZ) wrote:

      > Do any of the WSJT modes use bit rates and error correction coding
      > optimized to compensate for signal fluctuations due to constructive and
      > destructive interference of specular reflections along a meteor trail?
      > If so, at what frequency are Fresnel oscillations presumed to occur?
      > 73,
      > Ross N0GSZ

      The simple answer is no.

      The modes intended for meteor scatter and ionospheric scatter, namely
      FSK441 and JT6M, do not include forward error correction.

      As for periodic (or quasi-periodic) fading, although they sometimes
      occur I have seen no evidence that a modulation scheme could be readily
      optimized so as to compensate for it. The fading rate depends on
      wavelength and on reflection geometry, so a single solution would be a
      compromise at best.

      My experience over 8 years of playing with these signals is that a fast
      data rate is more important than anything else. FSK441 is thus designed
      to use the fastest data rate consistent with the bandwidths of our SSB
      transceivers.

      -- 73, Joe, K1JT
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