Loading ...
Sorry, an error occurred while loading the content.
 

Re: [wsjtgroup] Do you think a sound card interface can make a difference?

Expand Messages
  • Joe Taylor
    Bob -- ... When something sounds too good to be true, it usually is. Specifications of sound cards that refer to the S/N of the card are completely
    Message 1 of 13 , Nov 7, 2005
      Bob --

      > RigExpert is not a program but it is more than an interface box. It
      > contains both an interface AND an external sound card. It is this
      > external sound card that provides a 10db S/N improvement over internal
      > sound cards.

      When something sounds too good to be true, it usually is.

      Specifications of sound cards that refer to the "S/N" of the card are
      completely irrelevant to use of the card with WSJT -- or indeed just
      about any other ham radio software. The reason is that the
      signal-to-noise ratio that matters for MS or EME (with WSJT), or for HF
      use of PSK31, is determined far upstream of the device interfacing your
      radio to your computer.

      A sound card would have to be EXTREMELY poor -- so poor that it would be
      unacceptable for "normal" computer uses such as recording/playing music,
      etc. -- before its S/N rating would significantly degrade the decoding
      ability of WSJT and similar programs.

      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 dBs weaker, and entirely negligible.

      As it happens, there is one way in which poor sound cards can adversely
      affect WSJT signals. It's not S/N, but rather inaccuracies in sampling
      rate. WSJT uses a sample rate of 11025 Hz for both input and output.
      All sound cards claim to support this rate, but some do it by
      interpolating rather poorly from another sampling rate.

      The Rig Expert may be a convenient way to do your radio-computer
      interfacing, but it will NOT gain you 10 dB (or even 1 dB) in detecting
      weak meteor pings or EME signals.

      -- 73, Joe, K1JT
    • Bob Poortinga
      ... Doesn t sampling jitter also introduce noise? Wouldn t a highly-stable sampling clock produce a lower noise floor resulting in better decodes? ...
      Message 2 of 13 , Nov 8, 2005
        Joe Taylor K1JT <joe@...> writes:

        > As it happens, there is one way in which poor sound cards can adversely
        > affect WSJT signals. It's not S/N, but rather inaccuracies in sampling
        > rate.

        Doesn't sampling jitter also introduce noise? Wouldn't a highly-stable
        sampling clock produce a lower noise floor resulting in better decodes?

        > The Rig Expert may be a convenient way to do your radio-computer
        > interfacing, but it will NOT gain you 10 dB (or even 1 dB) in detecting
        > weak meteor pings or EME signals.

        Thanks, Joe, I was simply looking for a definitive answer in response to
        the claims of others.

        73 de
        --
        Bob Poortinga K9SQL
        Bloomington, Indiana US
      • Joe Taylor
        ... Yes, but for any plausible amount of jitter that noise will cause negligible degradation of the WSJT audio signals sent from your radio to the sound card
        Message 3 of 13 , Nov 8, 2005
          Bob Poortinga wrote:
          > Joe Taylor K1JT <joe@...> writes:
          >
          >>As it happens, there is one way in which poor sound cards can adversely
          >>affect WSJT signals. It's not S/N, but rather inaccuracies in sampling
          >>rate.
          >
          > Doesn't sampling jitter also introduce noise? Wouldn't a highly-stable
          > sampling clock produce a lower noise floor resulting in better decodes?

          Yes, but for any plausible amount of jitter that noise will cause
          negligible degradation of the WSJT audio signals sent from your radio to
          the sound card input.

          The "inaccuracies in sampling rate" that I mentioned are not jitter, but
          rather a sampling rate that is constant but offset from the nominal
          value by a significant amount. WSJT always requests a sampling rate of
          11025 samples per second. The actual sample rate can be somewhat
          different. Some recent sound cards are "off" by as much as 75 Hz,
          sampling at about 11100 Hz instead of 11025. If uncorrected, this means
          that the WSJT tone spacing will be off by about 0.7% in both time and
          frequency, causing a loss of sensitivity up to about 2 dB.

          The next WSJT version to be released will have the ability to correct
          for errors in sound card sample rates.

          >>The Rig Expert may be a convenient way to do your radio-computer
          >>interfacing, but it will NOT gain you 10 dB (or even 1 dB) in detecting
          >>weak meteor pings or EME signals.
          >
          >
          > Thanks, Joe, I was simply looking for a definitive answer in response to
          > the claims of others.
          >
          > 73 de Bob, K9SQL

          Happy to help!

          -- 73, Joe, K1JT
        • Paul Whatton
          Hi Joe Do you have any examples so we know which sound cards to avoid? For example at the moment I m using a cheap OEM PCI soundcard. I also have an external
          Message 4 of 13 , Nov 8, 2005
            Hi Joe

            Do you have any examples so we know which sound cards to avoid? For
            example at the moment I'm using a cheap OEM PCI soundcard. I also have
            an external Soundblaster USB card so I wonder if there would be a real
            advantage in using that instead?

            Paul G4DCV

            PS the facility to click on and decode pings & bursts in real time in
            5.8.6 is wonderful!

            Bob Poortinga wrote:
            > Joe Taylor K1JT <joe@...> writes:
            >
            > > As it happens, there is one way in which poor sound cards can adversely
            > > affect WSJT signals. It's not S/N, but rather inaccuracies in sampling
            > > rate.
            >
          Your message has been successfully submitted and would be delivered to recipients shortly.