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9167Re: [wsjtgroup] JT65/JT4 - Max sync values + frequencies

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  • Joe Taylor
    Oct 1, 2012
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      Hi Bo,

      OZ2M wrote:
      > I wonder what is the highest possible "sync value" in JT65 and JT4 respectively? Even if I connect two PCs directly to each other I have not seen values above say 28. E.g. shouldn't it be 63 for JT65?

      The sync value is a relative indicator only. It's not calibrated in any
      particular units, and is necessarily linear. Its sole purpose is to
      help establish whether a signal of the relevant mode is present at
      particular time and frequency offsets DT and DF.

      > Frequencies
      > I have seen several values for the highest tone in JT65. For JT65C I have seen values from 685 Hz to 711 Hz. However, using the math from "The JT65 Communications Protocol, March 9, 2005" I cannot get anything else than ~700 Hz (JT65C) above the sync tone.
      >
      > Tone_N = Multiplier * (N+2) * 11025/4096, were
      >
      > Multiplier: ~A = 1, ~B = 2 and ~C = 4
      > N: 0 to 63
      >
      > Thus for JT65C:
      > Tone_0 = 4 * 2 * 11025 / 4096 = 21,533203125 Hz above sync
      > Tone_63 = 4 * 65 * 11025 / 4096 = 699,8291015625 Hz above sync

      Your numbers are correct. The figure 711 Hz is a good approximation for
      the total occupied bandwidth of a JT65C signal, which is 66*4*11025/4096
      = 710.5957... Hz (one tone spacing more than the figure 699.829... that
      you calculated).

      -- 73, Joe, K1JT
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