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Re: [tracker2] Correct RX audio level for OT2m modem?

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  • James Ewen
    ... Just in case you haven t run across this in the Wiki yet. http://wiki.argentdata.com/index.php/OT-Moto The audio level at pin 11 is acceptable. I feed the
    Message 1 of 3 , Jun 2, 2011
      On Thu, Jun 2, 2011 at 2:07 PM, hannihe <hessu@...> wrote:

      > Going to try it out as a KISS modem on a digipeater with a Motorola Radius radio.

      Just in case you haven't run across this in the Wiki yet.

      http://wiki.argentdata.com/index.php/OT-Moto

      The audio level at pin 11 is acceptable. I feed the TX audio into the
      flat audio input on pin 5. There is no preemphasis on the signal, so
      it doesn't meet spec, but I haven't run across anything that is
      barking about not being able to decode the tones after deemphasis.
      Besides, Kenwood doesn't meet spec with their gear either!

      It would be nice to be able to adjust the individual tone levels as in
      the TT4, but it seems to be working fine around here, with the unit
      being our main digipeater.

      If you feed the audio into the mic input on pin 2, you won't be able
      to get enough drive level, even if if you short out the resistor on
      the OT2 output circuit. I have another digipeater running with the
      audio fed into pin 2, and the levels maxed out. It only does about 2
      kHz deviation, but I can decode it about 45 km away. Maybe with a bit
      more drive I would get a better copy, but I need to go out to the site
      and change the pin and settings. It's only about 3 hours east of here,
      so it will be a couple days before I get a chance to get out there
      again.

      These OT2 units are sure nice!

      James
      VE6SRV
    • Gary Sanders
      ... Before I left for Dayton (I STILL haven t gotten back home yet!) I ran into this exact same problem with a Motorola Spectra and an OT1+. I batted my head
      Message 2 of 3 , Jun 2, 2011
        On 6/2/2011 9:48 PM, James Ewen wrote:
        >
        > If you feed the audio into the mic input on pin 2, you won't be able
        > to get enough drive level, even if if you short out the resistor on
        > the OT2 output circuit. I have another digipeater running with the
        > audio fed into pin 2, and the levels maxed out. It only does about 2
        > kHz deviation, but I can decode it about 45 km away. Maybe with a bit
        > more drive I would get a better copy, but I need to go out to the site
        > and change the pin and settings. It's only about 3 hours east of here,
        > so it will be a couple days before I get a chance to get out there
        > again.
        >
        > These OT2 units are sure nice!
        >
        > James
        > VE6SRV

        Before I left for Dayton (I STILL haven't gotten back home yet!) I ran
        into this exact same problem with a Motorola Spectra and an OT1+. I
        batted my head against the wall trying to fix it. When I'd crank up the
        OT1 tx audio level, the distortion on the scope was horrible, and I
        still had only about 2 khz of deviation. The twist was all screwed up also.

        I finally got a Velleman K1803 "Universal Mono Pre Amplifier" kit for
        around 12 bucks. It's just a simple 1 IC mono preamp that could be
        breadboarded in a few minutes, but the kit eliminated the hassles of
        rounding up parts, making a board, etc.

        I put it between the OT1 and the Spectra Mic In, cranked down the OT1
        audio output, which greatly improved the distortion, and set the
        deviation with the preamp. I now have plenty of drive, and the twist is
        perfect.

        The Motorola mic inputs seem to demand a LOT of audio drive, I guess
        that's a relic of the carbon mic days.

        Gary WB0BZR
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