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SignaLinkUSB freq response and S/N

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  • Peter Frenning [OZ1PIF]
    Has anyone else tried to characterize the SignaLinkUSB frequency response and S/N properties? I Have, and, to put it mildly, I m underwhelmed. Compared to my
    Message 1 of 3 , Sep 3 2:55 AM
      Has anyone else tried to characterize the SignaLinkUSB frequency response and S/N properties?

      I Have, and, to put it mildly, I'm underwhelmed. Compared to my old homebrew interface combined with an aged SoundBlaster16 PCI it sucks as far as pure data is concerned (I have spectralab dumps to document my statements; if anyone are interested mail me directly)

      The real interesting question here is: how important is this in real life? Both interfaces work fine doing everyday PSK31, RTTY, SSTV etc, but how critical does it become when working signals near the detection limit as in WSJT JT65, FSK441 and very weak HF PSK31?

      Why not just continue with the old setup? well, my new LapTop doesn't have serial ports and my radio (FT-847) no VOX; I do need more than one Soundcard, and I need something that'll work with Linux. All in all the SignaLinkUSB sounded attractive judged from reviews and blurbs....
      -- 
      Vy 73 de OZ1PIF/5Q2M, Peter
      
      ** CW: Who? Me? You must be joking!! **
      email: peter(no-spam-filler)@...
      http://www.frenning.dk/oz1pif.htm
      Ph. +45 4619 3239
      Snailmail:
      Peter Frenning
      Ternevej 23
      DK-4130 Viby Sj.
      Denmark
      ***********************************
      
      
      
    • Joe Taylor
      Hi Peter, ... I would be interested in seeing your data for the SignaLink device. The soundcard frequency response that s important for digital modes (at
      Message 2 of 3 , Sep 3 11:22 AM
        Hi Peter,

        Peter Frenning [OZ1PIF] wrote:

        > Has anyone else tried to characterize the SignaLinkUSB frequency
        > response and S/N properties?
        >
        > I Have, and, to put it mildly, I'm underwhelmed. Compared to my old
        > homebrew interface combined with an aged SoundBlaster16 PCI it sucks as
        > far as pure data is concerned (I have spectralab dumps to document my
        > statements; if anyone are interested mail me directly)

        I would be interested in seeing your data for the SignaLink
        device.

        The soundcard "frequency response" that's important for
        digital modes (at least as I have coded them in WSJT) is
        *not* the digitized amplitude as a function of frequency.
        It's also unimportant for the soundcard to have a very low
        noise figure (high dynamic range) -- as long as the
        essential selectivity against strong unwanted signals is
        established by the SSB filter in your radio. This is nearly
        always the case.

        What *is* important is that the soundcard's sample-rate,
        both input and output, is reliably what the calling program
        wants it to be. For WSJT this is 11025 Hz. Many of today's
        cheap sound systems always sample at 48000 Hz; the data are
        then "resampled" by the driver to (supposedly) give the
        requested rate. Some drivers do an amazingly bad job of
        this, and that's where the biggest problems lie. It's why
        WSJT needs to have those annoying "sample-rate correction
        factors".

        > The real interesting question here is: how important is this in real
        > life? Both interfaces work fine doing everyday PSK31, RTTY, SSTV etc,
        > but how critical does it become when working signals near the detection
        > limit as in WSJT JT65, FSK441 and very weak HF PSK31?

        JT65 transmissions have 126 symbols. Therefore, to avoid
        significant symbol-synch errors the sample rate must
        therefore be known to better than 0.1%. Similar
        requirements apply to the other WSJT modes. This is why the
        WSJT User's Guide states on page 5:

        "7. Take note of two numbers in the first panel of the
        status bar at lower left of the main screen. After WSJT has
        been running for a minute or so they should stabilize at
        values close to 1.0000. If both numbers are between 0.9995
        and 1.0005, the input and output sampling rates of your
        soundcard are close to the nominal 11025 Hz. If either
        number is outside this range, enter it as Rate in (first
        number) or Rate out (second number) on the Options screen.
        WSJT will then make necessary adjustments for the incorrect
        hardware sampling rate or rates."

        -- 73, Joe, K1JT
      • Peter Frenning [OZ1PIF]
        ... I ll not repeat my my message here, just indicate which message it s about. I have been accused of damaging Tigertronics reputation and possibly their
        Message 3 of 3 , Sep 3 3:23 PM
          Peter Frenning [OZ1PIF] skrev:
          Has anyone else tried to characterize the SignaLinkUSB frequency response and S/N properties?

          .....
          I'll not repeat my my message here, just indicate which message it's about. I have been accused of damaging Tigertronics reputation and possibly their business with my statements. If indeed so, it was not my intention, and I sincerely apologize.

          My questions are still valid (even if my data are bogus, in which case I need to learn why), and I hope to get to the bottom of this. The fact still remains that my particular combination of Radio, Interface and computer, put together as recommended by the manufacturer, does exhibit a data transfer which does, on the evidence of my data, have some disturbing characteristics. Whether this is even significant, due to my errors or faulty equipment remains to be determined.

          I will report back to the groups, when I'm in the clear with this.
          -- 
          Vy 73 de OZ1PIF/5Q2M, Peter
          
          ** CW: Who? Me? You must be joking!! **
          email: peter(no-spam-filler)@...
          http://www.frenning.dk/oz1pif.htm
          Ph. +45 4619 3239
          Snailmail:
          Peter Frenning
          Ternevej 23
          DK-4130 Viby Sj.
          Denmark
          ***********************************
          
          
          
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