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Reviving my OT2M - Sensitivity and noise issues

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  • awaschka@bellsouth.net
    I traded trucks a year ago and am just now getting around to re-installing my setup, which is as follows: Garmin Nuvi 350, powered from separate switching
    Message 1 of 3 , Dec 30, 2012
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      I traded trucks a year ago and am just now getting around to re-installing my setup, which is as follows:

      Garmin Nuvi 350, powered from separate switching regulator, connected with ARgent data cable to:
      OT2M V1.0
      Connected to Kenwood TM-221, Tx through mike connector, Rx through external speaker jack

      I would prefer not to use the speaker jack, but found (in my previous installation), that I was not getting good decode performance using the mike connector Rx audio which is only about 0.1 Vpp into 10K, per Kenwood manual. I am using the Eq jumper. I found the note about the wrong value of C2, and I suspect that my unit is wrong, but since I'm using the Eq jumper, that would not seem to matter.

      Question: What level is required to drive the receive input of the Ot2m?

      When I connect up the mike connector with everything else hooked up, the radio stops receiving, I hear a high-pitched squeal (I think from the 350 speaker). When I disconnect either the mike connector, the port A connector to the Garmin or the FMI cable on the GArmin itself, everything goes back to normal. I suspect a ground loop of some kind as this setup was working in my other truck, but at the moment its got me baffled.

      Question: Any ideas on what might be going on here?

      Thanks,

      Al
    • awaschka@bellsouth.net
      A correction to my previous post. When fully connected, the Tm-221 does NOT stop receiving. And the intermittent warbly squeal is coming from the 221
      Message 2 of 3 , Dec 30, 2012
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        A correction to my previous post. When fully connected, the Tm-221 does NOT stop receiving. And the intermittent warbly squeal is coming from the 221 speaker, not the 350. It is very quiet, and seems to be synchronized with the blinking green light (GPS received?) on the OT2M. I still suspect some kind of a gorund loop. Looking on the OT2M schematic in the vicinity of the RS-232 port, I see all 4 data lines but I can not find a ground. Are the digital and analog grounds isolated in the OT2M?

        Thanks,

        Al


        --- In tracker2@yahoogroups.com, "awaschka@..." <awaschka@...> wrote:
        >
        > I traded trucks a year ago and am just now getting around to re-installing my setup, which is as follows:
        >
        > Garmin Nuvi 350, powered from separate switching regulator, connected with ARgent data cable to:
        > OT2M V1.0
        > Connected to Kenwood TM-221, Tx through mike connector, Rx through external speaker jack
        >
        > I would prefer not to use the speaker jack, but found (in my previous installation), that I was not getting good decode performance using the mike connector Rx audio which is only about 0.1 Vpp into 10K, per Kenwood manual. I am using the Eq jumper. I found the note about the wrong value of C2, and I suspect that my unit is wrong, but since I'm using the Eq jumper, that would not seem to matter.
        >
        > Question: What level is required to drive the receive input of the Ot2m?
        >
        > When I connect up the mike connector with everything else hooked up, the radio stops receiving, I hear a high-pitched squeal (I think from the 350 speaker). When I disconnect either the mike connector, the port A connector to the Garmin or the FMI cable on the GArmin itself, everything goes back to normal. I suspect a ground loop of some kind as this setup was working in my other truck, but at the moment its got me baffled.
        >
        > Question: Any ideas on what might be going on here?
        >
        > Thanks,
        >
        > Al
        >
      • awaschka@bellsouth.net
        Even with radio squelch activated I am getting a very high FCS to RCV ratio. Searching for OT2 and 2211 I find a lot of messages indicating poor performance
        Message 3 of 3 , Jan 1, 2013
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          Even with radio squelch activated I am getting a very high FCS to RCV ratio. Searching for OT2 and 2211 I find a lot of messages indicating poor performance with the 2211 which, I supose was a key contributor to te OT2 being replaced with the OT3. Are there any mods to improve OT2 prformance, or do I just have to buy an OT3 on faith that it will do better?

          Sorry to re-hash this old subject but I have been off the APRS air for a year or more due to changing vehicles and I was just getting a hint of the problems when I traded my truck.

          Thanks,

          Al
          --- In tracker2@yahoogroups.com, "awaschka@..." <awaschka@...> wrote:
          >
          > I traded trucks a year ago and am just now getting around to re-installing my setup, which is as follows:
          >
          > Garmin Nuvi 350, powered from separate switching regulator, connected with ARgent data cable to:
          > OT2M V1.0
          > Connected to Kenwood TM-221, Tx through mike connector, Rx through external speaker jack
          >
          > I would prefer not to use the speaker jack, but found (in my previous installation), that I was not getting good decode performance using the mike connector Rx audio which is only about 0.1 Vpp into 10K, per Kenwood manual. I am using the Eq jumper. I found the note about the wrong value of C2, and I suspect that my unit is wrong, but since I'm using the Eq jumper, that would not seem to matter.
          >
          > Question: What level is required to drive the receive input of the Ot2m?
          >
          > When I connect up the mike connector with everything else hooked up, the radio stops receiving, I hear a high-pitched squeal (I think from the 350 speaker). When I disconnect either the mike connector, the port A connector to the Garmin or the FMI cable on the GArmin itself, everything goes back to normal. I suspect a ground loop of some kind as this setup was working in my other truck, but at the moment its got me baffled.
          >
          > Question: Any ideas on what might be going on here?
          >
          > Thanks,
          >
          > Al
          >
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