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DSP Squelch

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  • Tim Sawyer
    ... Unsquelched rx audio is a given (else there d be no noise) and very common on radios in repeater service. Pre-emp/de-emp thing could be a problem as that
    Message 1 of 3 , Aug 30, 2006
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      As for PL decode/squelch:

      1) Yes it is possible, BUT, the problem is that the input audio would have
      to be send straight from the receiver (pre-emphasized and unsquelched).



      Unsquelched rx audio is a given (else there'd be no noise) and very common on radios in repeater service. Pre-emp/de-emp thing could be a problem as that would effect how much noise gets to the DSP chip.


      2) Anything to do with software DSP decoding is processor intensive, and
      requires full access to the sound card.



      Yeah, and I have no idea if the embedded motherboard has enough processor for that sort of thing.


      3) Why replace a perfectly good squelch ciruit in the MASTR-II :)


      Because not everybody has a MSTR II. Your embedded system could add that much-sought-after motorola squelch to any japtrack. Plus you could do things like tighten or loosen the squelch remotely, you could change the hysteresis to 3, 6, or 10db, and the timing could be fine tuned. In short, you could have better squelch than motorola.

      I'm just thinking that more the embedded node can do the more attractive and cost-effective it becomes. As it is now it makes a pretty good basic repeater controller. I'm seriously thinking about replacing one of my older controllers with the node.


      :wq
      Tim



    • David Cameron - IRLP
      The motherboard has tons of unused power. I just dont have the knowledge or time to program the DSP functions.... There may be a way that you could split the
      Message 2 of 3 , Aug 31, 2006
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        The motherboard has tons of unused power. I just dont have the knowledge
        or time to program the DSP functions....

        There may be a way that you could split the left and right inputs of the
        sound card, one to feed pre-emp, one to feed de-emph, and process the two
        signals separately... In other words you would do DSP and PL detect on the
        pre-emp audio, and gate the de-emph audio.

        I dont know how one would write code to split the two channels into
        separate DSP streams in linux, but I am sure it could be done.

        Then you could control the audio mixing of the de-emph channel. The mixer
        is very versatile.

        Good ideas, but well out of the scope of what I can do now, sorry.

        Dave Cameron


        On Wed, 30 Aug 2006, Tim Sawyer wrote:

        >> As for PL decode/squelch:
        >>
        >> 1) Yes it is possible, BUT, the problem is that the input audio would have
        >> to be send straight from the receiver (pre-emphasized and unsquelched).
        >>
        >>
        >
        > Unsquelched rx audio is a given (else there'd be no noise) and very common on
        > radios in repeater service. Pre-emp/de-emp thing could be a problem as that
        > would effect how much noise gets to the DSP chip.
        >
        >
        >> 2) Anything to do with software DSP decoding is processor intensive, and
        >> requires full access to the sound card.
        >>
        >>
        >
        > Yeah, and I have no idea if the embedded motherboard has enough processor for
        > that sort of thing.
        >
        >
        >> 3) Why replace a perfectly good squelch ciruit in the MASTR-II :)
        >>
        >
        > Because not everybody has a MSTR II. Your embedded system could add that
        > much-sought-after motorola squelch to any japtrack. Plus you could do things
        > like tighten or loosen the squelch remotely, you could change the hysteresis
        > to 3, 6, or 10db, and the timing could be fine tuned. In short, you could
        > have better squelch than motorola.
        >
        > I'm just thinking that more the embedded node can do the more attractive and
        > cost-effective it becomes. As it is now it makes a pretty good basic repeater
        > controller. I'm seriously thinking about replacing one of my older
        > controllers with the node.
        >
        >
        > :wq
        > Tim
        >
        >
        >
        >
      • Ted Maczulat
        Hi Dave Not that I want to add to your overload. There is some stream splitting code in the listener package I use to record radio traffic for the volunteer
        Message 3 of 3 , Sep 1, 2006
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          Hi Dave

          Not that I want to add to your overload.

          There is some stream splitting code in the listener package I use to record
          radio traffic for the volunteer fire department here.

          In the source file "lsp.c" is simple but effective code to split the left
          and right channels into separate streams.
          http://www.vanheusden.com/listener/listener-1.7.2.tgz

          Just FYI

          Keep up the good work...and thanks...
          Ted, VE7TFM


          ----- Original Message -----
          From: "David Cameron - IRLP" <dcameron@...>
          To: <irlp-embedded@yahoogroups.com>
          Sent: Thursday, August 31, 2006 9:17 AM
          Subject: Re: [irlp-embedded] DSP Squelch


          > The motherboard has tons of unused power. I just dont have the knowledge
          > or time to program the DSP functions....
          >
          > There may be a way that you could split the left and right inputs of the
          > sound card, one to feed pre-emp, one to feed de-emph, and process the two
          > signals separately... In other words you would do DSP and PL detect on the
          > pre-emp audio, and gate the de-emph audio.
          >
          > I dont know how one would write code to split the two channels into
          > separate DSP streams in linux, but I am sure it could be done.
          >
          > Then you could control the audio mixing of the de-emph channel. The mixer
          > is very versatile.
          >
          > Good ideas, but well out of the scope of what I can do now, sorry.
          >
          > Dave Cameron
          >
          >
          > On Wed, 30 Aug 2006, Tim Sawyer wrote:
          >
          >>> As for PL decode/squelch:
          >>>
          >>> 1) Yes it is possible, BUT, the problem is that the input audio would
          >>> have
          >>> to be send straight from the receiver (pre-emphasized and unsquelched).
          >>>
          >>>
          >>
          >> Unsquelched rx audio is a given (else there'd be no noise) and very
          >> common on
          >> radios in repeater service. Pre-emp/de-emp thing could be a problem as
          >> that
          >> would effect how much noise gets to the DSP chip.
          >>
          >>
          >>> 2) Anything to do with software DSP decoding is processor intensive, and
          >>> requires full access to the sound card.
          >>>
          >>>
          >>
          >> Yeah, and I have no idea if the embedded motherboard has enough processor
          >> for
          >> that sort of thing.
          >>
          >>
          >>> 3) Why replace a perfectly good squelch ciruit in the MASTR-II :)
          >>>
          >>
          >> Because not everybody has a MSTR II. Your embedded system could add that
          >> much-sought-after motorola squelch to any japtrack. Plus you could do
          >> things
          >> like tighten or loosen the squelch remotely, you could change the
          >> hysteresis
          >> to 3, 6, or 10db, and the timing could be fine tuned. In short, you could
          >> have better squelch than motorola.
          >>
          >> I'm just thinking that more the embedded node can do the more attractive
          >> and
          >> cost-effective it becomes. As it is now it makes a pretty good basic
          >> repeater
          >> controller. I'm seriously thinking about replacing one of my older
          >> controllers with the node.
          >>
          >>
          >> :wq
          >> Tim
          >>
          >>
          >>
          >>
          >
          >
          >
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          >
          >
          >
          >
          >
          >
          >
          >
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