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Thread: GE MDX Mobiles

  1. #1
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    Post GE MDX Mobiles

    I'm just looking for some input here because the way I am looking at it, it seems to easy.

    I have two GE MDX mobile radios that I want to put together to use as a repeater.

    The pin out on the logic board is as follows.

    1 A- (Ground)
    2 Speaker Lo
    3 Speaker Hi
    4 External Mic Hi
    5 Switched A+ (+12 volts)
    6 G Star (Serial Request) (active Lo)
    7 External Push-to-talk (active Lo)
    8 Channel Guard Disable (active Lo)
    9 Switched Speaker Hi
    10 Audio Mute (active Lo)
    11 Volume-Squelch Hi
    12 Mic Lo
    13 Relay (active Lo)
    14 N.C.
    15 Display Serial
    16 Keypad Serial

    I basically want to piggy back the two radios with out using a controller for now, I just want to keep it simple at this point as I'm trying to learn how this stuff works and I don't want to get too crazy and go way over my head.

    so this is what is going on in my head

    RX Radio TX Radio
    Pin 2------------------>Pin 12
    Pin 3------------------>Pin 4


    No where I am lost is at the External PTT
    Im thinking Pin 13 on rx to Pin 7 on the TX radio.


    any input or help would be appreciated, I know using two maxtracs would probably be easier, but I'm always up for a challenge and willing to learn.


  2. #2
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    That should work with the fllowing modifications. What you will need is a pin that goes low on recieving a correct signal (carrier and pl). Pin13 may do this if its selectable in the software. This pin will go to pin 4 on the Tx radio. You may want to isolate this line line with a diode (1n4005) to prevent loading.

    The speaker hi line will have way too much audio on it I recommend a isolation capacitor in line (10 microfarad) plus a series resistor (10-100k) and a variable pot (470K) top to the 10-100k resistor mentioned, center to the mic hi line and bottom to ground (pin1) to drop the level to something the mic input can handle. You can scope pin 11 to see if the level is more usable but check to see if its only active when recieving the proper signal.

    If your more technically inclined I would look at connecting inside the radios rather than externally, there are better points to connect to.

  3. #3
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    I knew I am going to have to add some components I wasn't sure what the correct values would of been, I kinda figured that the speaker audio was going to be too much for the Mic Hi. The pins on the logic board on this series radio are actually in side the radio. I will post a photo.

    As far as the pins being selected in programming. I believe that what GE set the pins too that is what they are. Natarola thanks for you response is was very helpful
    Attached Images Attached Images

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    If you can locate them I would suggest the ceterpin of the deviation pot for the tx audio piont, the top of the volume control for the rx audio point. The ptt point is good unless the radio acts differently when this PTT is selected., The carried detect can be the Rx led indicator point on the front display. I believe that it only lights up when the proper carrier/tine is present. if the polarity is wrong (active high) you can run it through a 2n2222 transistor to "invert" the polarity. base input, emmiter to ground and collector to the ptt. use a 4.7 k to the measured high voltage on your rx indictor (ie on= 5v then the pullup goes to 5 volts) and the base and a 10k pullup to the collector. Once again you can add a 1n4005 diode from the collector to the ptt for isolation.

  5. #5
    vxo No Longer Registered

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    I'd also run a nice ground wire between the chassis of both radios. I've seen some disgusting ground loops before... don't wanna pop two perfectly good MDX's.

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    Quote Originally Posted by vxo View Post
    I'd also run a nice ground wire between the chassis of both radios. I've seen some disgusting ground loops before... don't wanna pop two perfectly good MDX's.
    Ya know I have been thinking. I've decided not to use the MDX's because they are really nice radios and I do not see too many of the UHF ones out there. I'm going to go with to maxtracs I picked up one of them cheap cables off ebay that plugs into the 16 pin jack on the back. Will see how that works. Its a same I have a R100 and a TK820R. The R100 doesn't want to work and the TK820 I can't find a programmer for it.

  7. #7
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    I have used tons of maytracs in the repeater mode with the patch cable. They work exellent. There is no need to play with rx/tx levels or anything. Just set up the option jack to phonepatch and connect the csq output (12) to the ptt (3) (active low) and the rx output (11) to the mic hi (2) and your all set to go.

  8. #8
    ka2fwn No Longer Registered

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    i use mdx's for just that and they work great.
    the mute line = cor , ptt=ptt,mic hi = tx audio in, vol sq hi = rx audio out. you dont need to program anything in the radio to make it work but freq n ctcss

  9. #9
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    I have the TKR820 programmer if you want to spend some money shipping the station back and forth, I can program it for you.