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

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  • 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 1 of 3 , Jun 2, 2011
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      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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