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Re: Decoding performance

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  • rt_tclay
    ... not ... decoders ... seen I don t know for sure, but I think the program just uses the green bar setting for the audio output filter width. I can copy
    Message 1 of 19 , Apr 26, 2008
      --- In dxatlas_group@yahoogroups.com, "bill_w4zv" <w0zv@...> wrote:
      >
      > Thanks Pete and Tor! Yes Tor, I simply had not discovered how to
      > increase the window size on the display.
      >
      > How do you feel about Skimmer's ability to decode weaker signals in
      > QSB and QRN? I'm somewhat unimpressed so far but it could be I'm
      not
      > doing something right. Does the DSP filter width affect all
      decoders
      > or just the one displayed with the green bar? Based on what I've
      seen

      I don't know for sure, but I think the program just uses the green
      bar setting for the audio output filter width.

      I can copy better than Skimmer on weak signals. If you watch it
      trying to copy a weak signal, it usually gets a few letters correct
      each time, but has a hard time putting together the full correct
      callsign. That's where the brain obviously has an advantage, when you
      are copying you can say definitely if you copied a particular letter
      and mark that mentally as "good copy".

      If on your computer Skimmer is reaching 100% cpu, then yes, it is
      having to reduce the number of decoders. I don't know the algorithm
      used to do that, but yes, it might do that based signal strength. Try
      reducing the bandwidth. My old 1GHz Athlon can't keep up with 96 KHz,
      but is ok at 48 KHz if the band isn't too busy.

      Tor
      N4OGW
    • Pete Smith
      ... Hi Bill - I think you may need to do some experimenting to maximize Skimmer s weak-signal performance. I may have mentioned this already, but a great deal
      Message 2 of 19 , Apr 26, 2008
        At 09:20 AM 4/26/2008, bill_w4zv wrote:
        >How do you feel about Skimmer's ability to decode weaker signals in
        >QSB and QRN? I'm somewhat unimpressed so far but it could be I'm not
        >doing something right. Does the DSP filter width affect all decoders
        >or just the one displayed with the green bar? Based on what I've seen
        >so far, Skimmer would be great for identifying strong stations CQ-ing
        >or in a pileup but it doesn't work very well for weaker signals, which
        >would likely be the very ones you want to know about. But this could
        >be due to my not setting Skimmer up correctly or due to my weak
        >computer.

        Hi Bill - I think you may need to do some experimenting to maximize
        Skimmer's weak-signal performance. I may have mentioned this already, but
        a great deal depends on the dynamic range of the line input of your
        soundcard. Whichever card you use, you need to make sure that the input
        gain is set just short of clipping, in order to get the closest possible
        approximation of the sensitivity of the receiver alone. and of course, you
        are comparing it with one of the best receivers ever made - no fair hi.

        73, Pete N4ZR
      • Pete Smith
        ... One of the most effective tricks is to uncheck the Adaptive decoder box, and set a specified maximum number of decoders. Hitting 100% isn t so
        Message 3 of 19 , Apr 26, 2008
          At 02:01 PM 4/26/2008, rt_tclay wrote:
          >If on your computer Skimmer is reaching 100% cpu, then yes, it is
          >having to reduce the number of decoders. I don't know the algorithm
          >used to do that, but yes, it might do that based signal strength. Try
          >reducing the bandwidth. My old 1GHz Athlon can't keep up with 96 KHz,
          >but is ok at 48 KHz if the band isn't too busy.


          One of the most effective tricks is to uncheck the "Adaptive" decoder box,
          and set a specified maximum number of decoders. Hitting 100% isn't so
          important, in my view, as eliminating most of the junk you get from
          Skimmer's trying to decode on RTTY signals. If you set a maximum number of
          decoders, Alex says that Skimmer accommodates that by narrowing the band of
          frequencies that it attempts to decode, centered around the center
          frequency of the waterfall display. Experimentally, I discovered that 150
          decoders seemed pretty much to eliminate anything above about 14060 on a
          normally busy weekend band, when I set the waterfall on 14030. Today,
          running 300 decoders, I'm getting a lot of "AA4EE" type "callsigns" in the
          14070 and above range. During a major contest, you might have to set it to
          a higher number to get the same approximate frequency coverage.

          73, Pete N4ZR
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