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Demodulator

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  • scott@opentrac.org
    As an experiment, I pulled the 2211 completely on a T2, and routed the analog input to an ADC pin (AC coupled and biased to 2.5 volts). I implemented a
    Message 1 of 5 , Sep 5, 2006
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      As an experiment, I pulled the '2211 completely on a T2, and routed the
      analog input to an ADC pin (AC coupled and biased to 2.5 volts). I
      implemented a simple correlator in software, and it's able to reliably
      distinguish between a 1200 hz and 2200 hz tone.

      So far I'm not having much luck beyond that. I've seen it decode at best 13
      consecutive characters. I'm not sure if I'll be able to get it working
      better than that, but I'll keep tweaking it. There are three main portions
      that need to be tuned - the correlator itself, the low-pass filter on the
      correlator output, and the clock recovery code. If anyone's familiar with
      this sort of thing, I'm welcome to input.

      Scott
    • Jason Winningham
      ... I m not, but Gary (N4TXI) designed the WhereAVR using a ZCD for audio input. Not sure about the actual success rate, but it worked well enough to receive
      Message 2 of 5 , Sep 10, 2006
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        >
        > If anyone's familiar with this sort of thing, I'm welcome to input.

        I'm not, but Gary (N4TXI) designed the WhereAVR using a ZCD for audio
        input. Not sure about the actual success rate, but it worked well
        enough to receive short messages used for cutdown commands.

        http://www.knology.net/~gdion/whereavr.html


        -Jason
        kg4wsv
      • scott@opentrac.org
        Yeah, I ve seen the WhereAVR, and it sounds like it was kind of marginal. I want to be able to do better than that, but I really don t know if it s going to
        Message 3 of 5 , Sep 10, 2006
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          Yeah, I've seen the WhereAVR, and it sounds like it was kind of marginal.  I want to be able to do better than that, but I really don't know if it's going to happen in an 8-bit MCU at 7.3 MHz.
           
          The really interesting thing is that the OpenTracker has the same hardware setup - if I can decode packets with the T2's ADC, I can do it with the OpenTracker as well.  Of course, the OT1 still doesn't have enough RAM to really do much with it, but maybe I could expand the Packet Shooter firmware into a very primitive bidirectional KISS device.
           
          Scott


          From: tracker2@yahoogroups.com [mailto:tracker2@yahoogroups.com] On Behalf Of Jason Winningham
          Sent: Sunday, September 10, 2006 5:55 AM
          To: tracker2@yahoogroups.com
          Subject: Re: [tracker2] Demodulator

          >
          > If anyone's familiar with this sort of thing, I'm welcome to input.

          I'm not, but Gary (N4TXI) designed the WhereAVR using a ZCD for audio
          input. Not sure about the actual success rate, but it worked well
          enough to receive short messages used for cutdown commands.

          http://www.knology. net/~gdion/ whereavr. html

          -Jason
          kg4wsv

        • scott@opentrac.org
          A quick follow-up to this... I spent some time tweaking the performance and still wasn t happy with how it was working, but when I happened to take a look at
          Message 4 of 5 , Sep 11, 2006
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            A quick follow-up to this... I spent some time tweaking the performance and still wasn't happy with how it was working, but when I happened to take a look at the radio I was testing it with I found that it was 5 kHz off frequency, despite having the keypad lock on!  Seems to happen every once in awhile.  Anyway, it *will* decode some packets using the software-based delay line correlator.  I sent it a command from my D7A and it responded appropriately.  I'm still not convinced the performance will ever be great, but it should at least allow some interesting features on the original OT1 hardware.
             
            Scott


            From: tracker2@yahoogroups.com [mailto:tracker2@yahoogroups.com] On Behalf Of scott@...
            Sent: Sunday, September 10, 2006 12:32 PM
            To: tracker2@yahoogroups.com
            Subject: RE: [tracker2] Demodulator

            Yeah, I've seen the WhereAVR, and it sounds like it was kind of marginal.  I want to be able to do better than that, but I really don't know if it's going to happen in an 8-bit MCU at 7.3 MHz.
             
            The really interesting thing is that the OpenTracker has the same hardware setup - if I can decode packets with the T2's ADC, I can do it with the OpenTracker as well.  Of course, the OT1 still doesn't have enough RAM to really do much with it, but maybe I could expand the Packet Shooter firmware into a very primitive bidirectional KISS device.
             
            Scott


            From: tracker2@yahoogroup s.com [mailto:tracker2@ yahoogroups. com] On Behalf Of Jason Winningham
            Sent: Sunday, September 10, 2006 5:55 AM
            To: tracker2@yahoogroup s.com
            Subject: Re: [tracker2] Demodulator

            >
            > If anyone's familiar with this sort of thing, I'm welcome to input.

            I'm not, but Gary (N4TXI) designed the WhereAVR using a ZCD for audio
            input. Not sure about the actual success rate, but it worked well
            enough to receive short messages used for cutdown commands.

            http://www.knology. net/~gdion/ whereavr. html

            -Jason
            kg4wsv

          • Jason Winningham
            ... yay, balloon cutdown with an OT1 - no more DTMF boards! (: -Jason kg4wsv
            Message 5 of 5 , Sep 11, 2006
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              On Sep 11, 2006, at 11:33 AM, <scott@...> wrote:

              > but it should at least allow some interesting features on the original
              > OT1
              > hardware.

              yay, balloon cutdown with an OT1 - no more DTMF boards!

              (:

              -Jason
              kg4wsv
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