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Adapting a Garmin Traffic Receiver to car antenna?

Discussion in 'Electrical Engineering' started by DaveC, Feb 23, 2010.

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  1. DaveC

    DaveC Guest

    Garmin makes an "integrated" FM traffic info receiver for some models of GPS
    that allows connection to the car's AM/FM antenna. But not my model (Nuvi
    660); I must use only the GTM20, a cigarette-lighter-powered model:


    Benefits of using the car's antenna are mostly stealth: the
    cord-that-is-the-antenna between the cigarette lighter (which will be
    relocated inside the glove box) and the GPS plug that lays on the dashboard
    makes for an advertisement to crooks. And the car's antenna would, arguably,
    work better.

    What are my options re. adapting the GTM20 to work with the car's antenna?
    Could this be as simple as splicing in a motorola antenna plug to the cable?


  2. DaveC

    DaveC Guest

    The car's antenna probably won't work better.
    Maybe I should explain a little...

    The FM Traffic service is a supplementary broadcast subscription service
    using some sub-carrier of the FM broadcast band (88-108 MHz). It carries
    traffic "events" information (accidents, roadwork, etc.). The receiver is
    located within the cigarette-lighter power adapter, and the antenna is in the
    6-foot cable between the adapter and the plug that attaches to the GPS

    So we're talking broadcast band here, not GPS band.
  3. Rich Webb

    Rich Webb Guest

    I think he's looking for a solution to the "live traffic update" option
    and not the GPS signal itself. Traffic info (at least in CONUS) is
    carried on the FM spectrum as a side channel to one or more local

    I've got one of these gizmos also (came with the GPS) and from the looks
    of it I'd hesitate to slice into it. It might be enough to just wrap a
    few turns of wire around it and connect the free end of the wire to the
    car's antenna lead. You're only interested in traffic info from local
    stations, which are probably strong enough to work with this.
  4. ps56k

    ps56k Guest

    huh ?

    The "integrated" FM antenna (for traffic info)
    is located inside the power adapter module,
    and does not connect to anything else besides the GPS mini-USB.

    Exactly what product connects to "the car's FM antenna" ?

    In case you think the GPS receives location info via that FM module,
    it does not.... it is only for traffic info from the radio stations.

    If you are looking for using an external GPS antenna - that is a totally
    different question.
  5. Rich Webb

    Rich Webb Guest

    Belay my last... It looks like the newer GTM-20 models do in fact have
    a receptacle for a connector to an external antenna. Mic'ing it out, the
    diameter looks like it takes a 1/8" plug (3.5 mm is too large). The
    (fuzzy) picture in the manual shows just a tip/ring configuration
    (reasonable for an antenna) and claims that it's available at the Garmin
    store. Their store search is abysmally bad, though, so if it's even
    there it'll take patience finding it.
  6. ps56k

    ps56k Guest

    Where is the antenna connector you are talking about ?

    This photo shows the 12v DC tubular connector - with the 12v center pin
    contact -
    and going to the special 18-pin flat connector for the GPS
  7. ps56k

    ps56k Guest

    All of these receivers have the Traffic FM receiver module embedded in the
    DC adapter, on inline on the power cable -

    AND - as per the manuals -
    some DO HAVE a special connector for an external antenna
    which in the manual appears to be located directly on the inline module...

    In looking over this list - and actually downloading the manuals,
    it's hard to tell the difference between them -
    and the "18-pin flat plug" is for those special CRADLE mounts,
    while others are for the mini-USB on the GPS itself...

    It is a bit confusing - even have the GTM-20 listed twice,
    but with different hardware features...
  8. DaveC

    DaveC Guest

    The "integrated" FM antenna (for traffic info)

    The different pigtail connectors (scroll down) adapt the receiver to the
    car's antenna.
    Yes I know.
  9. DaveC

    DaveC Guest

    I wired the receiver for my 680 to an accessory jack that's switched
    My original question is how to tap the FM traffic receiver into the car's
    radio antenna.
  10. DaveC

    DaveC Guest

    All of these receivers have the Traffic FM receiver module embedded in the
    As far as I could find, only the GTM10 is listed as requiring "professional
    installation" (ie, having capability of using the car antenna and/or power
    from other than the cigarette lighter):


    All others use some kind of cigarette-lighter power adapter and have it's own
    It's the cradle-mount FM receiver / power adapter that is unique to the 660
    and is found only in the GTM20.
    In a conversation with Garmin tech support, I learned that there are 2 GTM-20
    receivers: pn 010-00544-01 and pn 010-00544-13. The only difference is that
    the -13 comes with lifetime traffic service and the -01 comes with a trial
    service (6-months or 10 months -- both were offered).
  11. ullim

    ullim Guest

    Where is the antenna connector you are talking about ?

    Hmm the GTM-25 shipped with my 1490T has a stereo mini-jack plug for antenna
    cable (included in the package) on the side of the receiver.
  12. Rich Webb

    Rich Webb Guest

    From what I can tell, the two parts that are labeled GTM-20 are also
    physically different. The original, with the 6/10 month trial, had a
    uniform cord between the 12 V plug and the GPS-side connector. The newer
    one, with the lifetime subscription, has a molded section near the GPS
    terminus which includes the receptacle for an external antenna
  13. DaveC schreef:
    Is the VIB11 from Garmin the solution for you? It uses the carantenna
    for receiving the traffic messages.
  14. Steve Stone

    Steve Stone Guest

    A few days ago I picked up a Garmin NUVI 285WT for $100 from
    I was configuring it indoors and trying to activate the MSN traffic
    service 9 month trail.
    I could not get a good enough signal indoors so I connected a piece of
    coax to the wall jack leading to our outdoor TV antenna, put a jumper
    wire with an alligator clip on the inner wire of the coax and wrapped
    the jumper wire around the NUVI power cord (which includes the traffic
    receiver) and the signal strength increased to 100 percent, all bars lit
    green, allowing me to activate the traffic software. I wonder if a
    similar technique would work with a car radio antenna?

  15. Because that's not what they are talking about. As stated in the posts
    and in the subject line, they are talking about the traffic receiver,
    which uses FM radio signals.
  16. krw

    krw Guest

    You have to understand AlwaysWrong. He's *always* wrong.
  17. He posted a reply to my post about the same time you did. I am beginning to
    see what you mean.

    Also, I hadn't looked at his headers before - a serious misstep on my
  18. Steve Stone

    Steve Stone Guest

    Bart, you old fart.....

    This is not a GPS frequency.
    Traffic data is piggy backed on broadcast band FM frequencies.
    An external GPS antenna won't do squat to fix this issue.

    You need more fiber in your diet.
    Have a nice day!
  19. Steve Stone

    Steve Stone Guest

    It should but it does not.
    It plugs into the USB port on the back of the GPS.
    The USB port is used to data signal and power to recharge the built in

    the cable is wired like this

    12 VDC power plug,

    A couple of inches of DC power cord to an approx. 2 inch oblong FM receiver

    From the FM receiver 2 cables go to the GPS USB port, one is data/power,
    the other is used as a broadcast band FM antenna , hanging inside your car.

    Hacking the assembly would require cracking open the sealed FM receiver
    without damaging the device, figuring out where the antenna wire input
    is located, and soldering in an antenna input jack and an A/B switch ,
    sealing up the unit (voiding any warranty).

    Do you suggest I put the device in my shop vice,
    apply pressure till it cracks open or turns to shrapnel, or dig out the
    dremel tool?

    I prefer inductive coupling to hacking a device still under warranty.

    73 de N2UBP
  20. Rich Webb

    Rich Webb Guest

    You must be new here. This month the kill-file log shows that he is
    using the following aliases, sorted by number of entries. Better to just
    ignore him. Don't feed the trolls and all that...

    1: CellShocked <>
    1: VioletaPachydermata
    2: Abbey Somebody <>
    2: SoothSayer <>
    2: TralfamadoranJetPilot
    3: ""
    4: Bungalow Bill <>
    4: Pieyed Piper <>
    6: UltimatePatriot <>
    8: Lil Red Riding In The Hood
    8: TheJoker
    11: Son of a Sea Cook <>
    15: Mycelium <>
    17: AwlSome Auger <>
    17: Bart! <[email protected]_The_Sheriff_Is_A_Nig***!.org>
    21: "Herbert John \"Jackie\" Gleason"
    21: Capt. Cave Man <>
    25: StickThatInYourPipeAndSmokeIt <>
    34: Archimedes' Lever <>
    40: FatBytestard <>
    413: life imitates life <>
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