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Re: [MT63] What am I missing

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  • Tom Consodine ND5Y
    I have occasionally seen MT63 stations that I was not able to copy and never figured out why. Make sure the MixW sample rate is 8000 or 11025 Hz. I accidently
    Message 1 of 5 , Oct 11, 2003
      I have occasionally seen MT63 stations that I was not able to copy and never
      figured out why.

      Make sure the MixW sample rate is 8000 or 11025 Hz. I accidently changed mine
      once and some modes would not work properly.

      Use the sound card clock adjust function in MMSSTV
      (an excellent SSTV sound card software in case you have never heard of it)
      to determine if the sound card clock is off frequency.
      If it is way off, it might affect copy.

      MMSSTV has an excellent feature that measures the sound card clock error in
      parts per million while receiving WWV/WWVH. You then enter that value into MixW's
      sound card settings. It is much easier to use and see than the calibration
      function in MixW.

      I'm surprised that Navy MARS allows you guys to use advanced
      sound card modes like that.

      Tom ND5Y

      >
      > All,
      >
      > I trying to help a freind who is having trouble copying MT63. He gets
      > mostly garbage with occasionallty a word or two. Signals that others
      can
      > copy on MARS nets he has trouble with. He has the same problem with
      > IZ8BLY
      > MT63 and MixW.
      >
      > We have been communicating via radio, email and telephone. Here is
      the
      > list
      > of I have checked but still no joy;
      >
      > He has used two different computers. I know one of them, his primary
      one,
      > is a Pentiurm III.
      >
      > All radio filters are wide.
      >
      > He has a simple receive only set-up and copies soundcard Amtor and
      PSK31
      > with no problem.
      >
      > He is getting a strong waterfall pattern placed exactly between the
      lines.
      >
      > All operations have been on USB.
      >
      > "Paper" is on in IZ8BLY
      >
      > He mostly get an "Out of synch" and low confidence readings (with
      IZ8BLY).
      >
      > Mode is set correctly- we have tried 1000 and 2000Hz (on the MARS
      > frequencies) with long interleave.
      >
      > I am out of ideas. Here it is hard not to get solid copy on MT63
      > signals....even with a laptop with no interface (just sound from the
      radio
      > speaker), and signals over 100 Hz off freq.......so what am I missing.
      I
      > would really like to help him with this mode which is ideal for MARS
      FEC
      > traffic handling under poor conditions.
      >
      > Thanks
      >
      > de Bill
      > KB4IJ/NNN0TJC
    • Tomi Manninen
      ... MT63 is _very_ sensitive to samplerate errors. It doesn t need to be way off to completely destroy performance. Pawel s original notes mention needing
      Message 2 of 5 , Oct 11, 2003
        On Sun, 2003-10-12 at 03:34, Tom Consodine ND5Y wrote:

        > Use the sound card clock adjust function in MMSSTV
        > (an excellent SSTV sound card software in case you have never heard of it)
        > to determine if the sound card clock is off frequency.
        > If it is way off, it might affect copy.

        MT63 is _very_ sensitive to samplerate errors. It doesn't need to
        be way off to completely destroy performance. Pawel's original
        notes mention needing better than 0.01% accuracy.

        Nowadays, it's not uncommon to see soundcards that are >1% off.

        So, like Tom says above, samplerate compensation is needed. On
        windows, I think MMSSTV and MixW at least have the tools to do this.

        --
        Tomi Manninen / OH2BNS / KP20ME04
      • jsb@digistar.com
        ... I ve had similar problems. I have tried plugging the output into the input of my soundcard(s) to send and receive at the same time from the same source
        Message 3 of 5 , Oct 13, 2003
          On Sat, 11 Oct 2003, Bill Ayer wrote:

          > I trying to help a freind who is having trouble copying MT63. He gets
          > mostly garbage with occasionallty a word or two. Signals that others
          > can copy on MARS nets he has trouble with. He has the same problem with
          > IZ8BLY MT63 and MixW.

          I've had similar problems. I have tried plugging the output into the
          input of my soundcard(s) to send and receive at the same time from the
          same source but it still fails. Other computers that I have used have
          worked fine.

          I have narrowed my problem down to my computer - I got a new Turtle Beach
          soundcard and that didn't fix the problem either.


          I believe this is caused by RF noise inside the computer case coming from
          the CPU or some other motherboard component - I can't figure what else
          might be causing it.


          It's also worth trying different wall outlets on different breakers.


          hope this helps,
          Jason
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