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  1. #1
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    Possible Light Interference with GPS?

    A couple of months ago, around the time change, I got a new Garmin Edge 500 GPS and Baja Designs Stryker II light. The GPS I mount on my stem and the light goes on the bars next to the stem (with the extra wire wrapped a few times around the stem spacers). For the first half dozen or so rides I noticed my GPS data would sometimes be off both in mileage and track...to the point that I started to also carry my Garmin 305 in my Camelbak as a backup. I contacted Garmin about it and they recommended I do a satellite realignment, which I did. That seemed to fix things and I haven't had any trouble for the past couple of weeks.

    Then last night I went for a ride and my Garmin 500 had a lot of trouble locating satellites. It took 10+ mins before it finally linked up. During the ride it was losing reception with the satellites and on the final hill back to my car I noticed my speed was showing 15-20 mph, when I know I was sub-10 mph. That got my thinking and I realized for the past couple of weeks I've been on vacation and only doing day rides. I decided to turn off my bar light and noticed that the speed reading seemed to drop back to normal and stabilize.

    So is this just a coincidence or could the light be interfering with the GPS signal and/or internal electronics? I've got a couple of lights and two GPS I can do some testing with, but I figured I'd throw the question out here to see what the interwebs thought.

  2. #2
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    Are you using a speed/cadence sensor? I'd guess that before the GPS signal. Check things out on a day ride.
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  3. #3
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    Nope. No speed or cadence sensor.

  4. #4
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    It seems quite possible that the light could produce some RF that when placed close to the GPS would hurt its ability to receive satellite reception. Try giving some space between them and see if that helps.
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  5. #5
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    Quote Originally Posted by yfz_duner View Post
    A couple of months ago, around the time change, I got a new Garmin Edge 500 GPS and Baja Designs Stryker II light. The GPS I mount on my stem and the light goes on the bars next to the stem (with the extra wire wrapped a few times around the stem spacers). For the first half dozen or so rides I noticed my GPS data would sometimes be off both in mileage and track...to the point that I started to also carry my Garmin 305 in my Camelbak as a backup. I contacted Garmin about it and they recommended I do a satellite realignment, which I did. That seemed to fix things and I haven't had any trouble for the past couple of weeks.

    Then last night I went for a ride and my Garmin 500 had a lot of trouble locating satellites. It took 10+ mins before it finally linked up. During the ride it was losing reception with the satellites and on the final hill back to my car I noticed my speed was showing 15-20 mph, when I know I was sub-10 mph. That got my thinking and I realized for the past couple of weeks I've been on vacation and only doing day rides. I decided to turn off my bar light and noticed that the speed reading seemed to drop back to normal and stabilize.

    So is this just a coincidence or could the light be interfering with the GPS signal and/or internal electronics? I've got a couple of lights and two GPS I can do some testing with, but I figured I'd throw the question out here to see what the interwebs thought.
    Possibly the fact that the Stryker being mounted close to the GPS is causing the problem. Some lamps use a PWM circuit ( Pulse width modulation ) to vary the output of the lamp for the different modes. If the driver on the lamp is not properly shielded the high frequency emissions of the driver might be picked up by the GPS receiver which in turn can cause a problem with how the GPS is operated.

    I suggest you post up on the sub forum the deals with GPS electronics ( on MTBR ) as the people who post there will likely have better answers. I'm also interested in this problem because I plan to by a Garmin later this year.

  6. #6
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    Very likely that a light could interfere with a GPS. The receiver in the GPS is pretty sensitive and almost any current light will have a PWM circuit to control it (dimming etc). If close, I'd actually be surprised if they didn't screw up the GPS in some manner. Switching power electronics and sensitive rf just aren't ever all that compatible.

  7. #7
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    Not the same thing but FYI my Go Pro stops my wireless computer from working properly. Only when it's recording video though, not in standby.

  8. #8
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    Went for a daytime ride yesterday and the Garmin recorded data just fine. Tonight I'll put the Garmin in my pocket and see how it does.

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