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Re: [wsjtgroup] sound cards

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  • jeff millar
    ... Digital radio design has very different requirements whether trying to digitize IF or digitize audio. When digitizing IF, the dynamic range includes
    Message 1 of 3 , Nov 8, 2005
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      Peter L. Jackson wrote:

      >If the card is placed external as in the case of a USB sound card, wont the
      >chance of internal injected hum, inter mods etc. be greatly reduced
      >than if residing internally in the PC.
      >Wouldn't S/R also be improved whether one is using WSJT or monitoring on a
      >waterfall looking at weak signal's in general ?
      >
      >Also can low latency ASIO audio drivers that allow high speed cw and
      >fast TR transition be also be of benefit ?
      >This seems to be the holy grail that the sdr-1000 flex radio forum
      >members are seeking to achieve.
      >
      >
      Digital radio design has very different requirements whether trying to
      digitize IF or digitize audio. When digitizing IF, the dynamic range
      includes strong signals in the passband and amplitude variations not
      handled by the AGC. When digitizing Audio, the dynamic range only needs
      to exceed the required signal to noise ratio by 10-15 dB. Radios that
      use digital filtering at IF to knock out the last few close in
      interferrers need maybe 80 dB dynamic range. But radios that digitzize
      WSJT audio can make due with about 40 dB dynamic range because the
      radio's IF filters take out the adjacent channel interferrers. Even the
      worst sound card probably has more than 60 dB dynamic range, so it's not
      critical.

      WSJT doesnt' need fast, low latency audio processing because the Tx/Rx
      cycle takes 30 seconds. Low latency would help with break-in CW or
      fast turnaround digital modes. Since Joe's software mostly deals with
      long integration time to improve weak signal performance, it's unlikely
      that T/R speed will ever drive the requirements.

      jeff, wa1hco
    • Joe Taylor
      Peter -- ... There is no reason for any well made sound card to introduce hum or distortion just because it is located inside a PC. Hum is almost always
      Message 2 of 3 , Nov 10, 2005
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        Peter --

        Peter L. Jackson wrote:
        > Hello Joe and fellow group members,
        >
        > I have been following this debate about sound cards with interest as its
        > a popular theme at the moment that crops up on various forums.
        > In your email to the group Joe ...
        >
        > />>>>The noise that the WSJT decoders must cope with is a combination of
        > cosmic noise, atmospheric noise, and receiver noise; sound card noise is
        > many tens of dB's weaker, and entirely negligible.<<<<</
        >
        > I take it that the referral to sound card noise is reference to the
        > particular chip set used along with associated components making up the
        > particular sound card.
        >
        > If the card is placed external as in the case of a USB sound card, wont the
        > chance of internal injected hum, inter mods etc. be greatly reduced
        > than if residing internally in the PC.
        > Wouldn't S/R also be improved whether one is using WSJT or monitoring on a
        > waterfall looking at weak signal's in general ?

        There is no reason for any well made sound card to introduce hum or
        distortion just because it is located inside a PC. Hum is almost always
        indicative of a ground-loop problem, and can usually be resolved with an
        audio isolation transformer between radio and computer. In addition,
        WSJT is relatively immune to hum because 50/60 Hz and the first
        half-dozen harmonics are well below the WSJT frequency range.

        > Also can low latency ASIO audio drivers that allow high speed cw and
        > fast TR transition be also be of benefit ?
        > This seems to be the holy grail that the sdr-1000 flex radio forum
        > members are seeking to achieve.

        No significant benefits to WSJT, which does not need extremely low latency.
        -- 73, Joe, K1JT
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