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Re: T2 demod questions

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  • Hank
    ... Tim, Take a look at t2protoc-schematic.png , Schematic for Proto C revision in the files section and you ll see the EQ jumper and C25 (.1) that gets put in
    Message 1 of 8 , Dec 4, 2007
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      > I was looking at the schematic in the YahooGroups file area to try
      > and see what the EQ jumper actually does.

      > I can't find the EQ jumper in the schematic to see what it's
      > supposed to do.

      Tim,

      Take a look at

      t2protoc-schematic.png , Schematic for Proto C revision

      in the files section and you'll see the EQ jumper and C25 (.1) that
      gets put in parallel with C1 (.01).

      > I'm looking at audio on both sides of the EQ jumper with and without
      > the jumper and see no difference in how the mark/space tones are
      > handled.

      That filter is a high pass. Without the jumper, the response
      rises and flattens out around 4.5 KHz.

      With the jumper, it's already flattened by 1 KHz, so both modem
      tones are treated just about equally (at about -5.7 dB average
      referenced to a 1k Ohm source unloaded).

      Without the jumper, 2 KHz is about 4.5 dB stronger than 1 KHz
      (both frequencies still on the skirt of the filter). There is
      also a higher passband loss without the jumper.

      Note that the passband loss of the filter is sensitive to the
      audio source impedance, and an input resistance of much over
      2k Ohms starts to show up in a progressively higher passband
      loss (chiefly due to the shunt 4.7 K Ohm resistor, R8).

      Without assessing the filter properly using a signal generator
      and level sensor (scope or meter), these response differences
      between jumper settings may not be evident.

      Hank
    • Tim Smith
      ... Thanks Hank...that sheds some light on the input circuit, but I m still having problems with the T2 being either a little deaf or not decoding a number of
      Message 2 of 8 , Dec 7, 2007
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        > Take a look at
        > t2protoc-schematic.png , Schematic for Proto C revision
        > in the files section and you'll see the EQ jumper and C25 (.1) that
        > gets put in parallel with C1 (.01).

        Thanks Hank...that sheds some light on the input circuit, but I'm
        still having problems with the T2 being either a little deaf or not
        decoding a number of packets for other reasons. I do not see much of
        a difference in EQ jumper impact, either in decoded packets or what I
        see on the scope in terms of mark/space levels. Both radios I have
        tried are discriminator-tapped (Icom and Alinco)...which are fixed
        level, but also tried full audio chain as well. In all cases, the
        software TNC is hearing much better than the T2.

        Scott...I did some side by side tests when deploying the T2 at our
        digi site. In comparing with two different radios using AGWPE with a
        SBII sound card, I was seeing the expected packets being decoded.
        However, when replacing the sound card TNC with the T2, I'm missing
        about 20% of the packets. I tried a wide range of levels from 50mv to
        2v ptp. There is one station that the T2 will not receive at all
        despite EQ settings, audio levels, etc (which happens to be an
        adjacent wide area digi).

        I began to notice this at home when letting the trial run in prep for
        the wide digi installation.

        Anyone else seeing problems with T2 deafness?

        Thanks,

        Tim
      • Scott Miller
        I ve had a couple of reports, but nothing consistent. You re always welcome to send it back for testing, and I ll run a full decode test against it to see how
        Message 3 of 8 , Dec 7, 2007
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          I've had a couple of reports, but nothing consistent. You're always
          welcome to send it back for testing, and I'll run a full decode test
          against it to see how it compares to the baseline - that'd tell us if
          there's a problem with your specific unit.

          Also, what is your power setup? I've had at least one report of bad
          decode performance that was caused by a noisy power system. Switching
          to battery power made the problem go away.

          I've had at least a couple of people report specifically that their T2
          did BETTER than AGWPE, and while I won't guarantee that'll always be the
          case it ought to be close.

          Scott

          Tim Smith wrote:
          >
          >
          >
          > > Take a look at
          > > t2protoc-schematic.png , Schematic for Proto C revision
          > > in the files section and you'll see the EQ jumper and C25 (.1) that
          > > gets put in parallel with C1 (.01).
          >
          > Thanks Hank...that sheds some light on the input circuit, but I'm
          > still having problems with the T2 being either a little deaf or not
          > decoding a number of packets for other reasons. I do not see much of
          > a difference in EQ jumper impact, either in decoded packets or what I
          > see on the scope in terms of mark/space levels. Both radios I have
          > tried are discriminator-tapped (Icom and Alinco)...which are fixed
          > level, but also tried full audio chain as well. In all cases, the
          > software TNC is hearing much better than the T2.
          >
          > Scott...I did some side by side tests when deploying the T2 at our
          > digi site. In comparing with two different radios using AGWPE with a
          > SBII sound card, I was seeing the expected packets being decoded.
          > However, when replacing the sound card TNC with the T2, I'm missing
          > about 20% of the packets. I tried a wide range of levels from 50mv to
          > 2v ptp. There is one station that the T2 will not receive at all
          > despite EQ settings, audio levels, etc (which happens to be an
          > adjacent wide area digi).
          >
          > I began to notice this at home when letting the trial run in prep for
          > the wide digi installation.
          >
          > Anyone else seeing problems with T2 deafness?
          >
          > Thanks,
          >
          > Tim
          >
          >
        • Tim Smith
          ... Thanks Scott...going to try a couple of more things and if no progress, I ll take you up on your offer. -Tim
          Message 4 of 8 , Dec 9, 2007
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            --- In tracker2@yahoogroups.com, Scott Miller <scott@...> wrote:
            >
            > I've had a couple of reports, but nothing consistent. You're always
            > welcome to send it back for testing, and I'll run a full decode test
            > against it to see how it compares to the baseline - that'd tell us if
            > there's a problem with your specific unit.

            Thanks Scott...going to try a couple of more things and if no
            progress, I'll take you up on your offer. -Tim
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