# Possible Light Interference with GPS?



## SoCal-Rider (May 25, 2009)

This is a cross-post from the Lights forum. They said to post in here too. 

Update to my original post over there: After a little more testing it's looking like it is the light causing the interference. I like having my time and mileage visible right in front of me on the GPS. Sucks I'll have to move it.

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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.


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## Harold (Dec 23, 2003)

Some lights are known to cause interference with old cyclocomputers. I think the first reports I heard of this were back when HID lights were first introduced to bike lights a decade or more ago. Back then, the interference was causing problems with wireless computers.

so it doesn't surprise me that a light is causing interference with your GPS. It's known (though maybe not expressed much here) that GPS receivers used side-by-side can interfere with each other. Even simple things can cause problems with GPS like your body position (your body can interfere with signal) and the orientation of the antenna (already a discussion covering that in here). And we already know that hills, trees, buildings, and cloud cover can attenuate GPS signal.

If you're using a wheel sensor with your Edge 500, then absolutely, the light definitely can be an issue. Even if not, it could also be interfering with the GPS satellite signal, since it's not all that strong (though it's still stronger than some other satellite signals like TV and sat radio).

You might play with your cable routing before you bail entirely. You say you wrap the light cable around your steerer a couple times? Steel steerer on the fork, right? You could be inducing a magnetic field in your steerer tube in doing that. You could work with your cable routing and see if that's enough to fix your problems.

Alternatively, you could try separating your light and your GPS to see if you can find a distance where you'll get the performance you want. Worst case scenario, I could see putting the light on your helmet with the GPS on the stem, or the GPS in your pack with the light on your bars. I think that's probably the farthest you will be able to get it from the GPS. Now, putting the GPS INSIDE a pack has its own issues with reception, but if you can get the GPS on top of the pack or on top of your helmet so the antenna still has a good view of the sky, you should be okay.

A good long term solution to this would be to shield the light head. I doubt there's any kind of aftermarket shielding that would not ruin the light head's heat dispersal capabilities, but I bet a light head could be built with a built-in EM shield that would eliminate or reduce interference with computers.


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## shiggy (Dec 19, 1998)

NateHawk said:


> Some lights are known to cause interference with old cyclocomputers. I think the first reports I heard of this were back when HID lights were first introduced to bike lights a decade or more ago. Back then, the interference was causing problems with wireless computers.


I had one of the first single LED "be seen" flashy headlights. It would add 15-20mph to my wireless computer. No interference in steady mode.


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## Gundam168 (Dec 19, 2012)

How did "light interfering with a GPS device" suddenly turn into a l"ight interfering with cyclocomputers"?


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## Harold (Dec 23, 2003)

Gundam168 said:


> How did "light interfering with a GPS device" suddenly turn into a l"ight interfering with cyclocomputers"?


Because for one, it establishes a pattern. Second, if the OP is using a wheel sensor for his GPS, it could explain where the interference is causing problems. Get your panties out of a wad.


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## slocaus (Jul 21, 2005)

Just put the troll in your Ignore list. Buh-bye. :thumbsup:


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## SoCal-Rider (May 25, 2009)

Jeez! Now I don't what to trust. I rode last night with my Garmin 500 in my right pocket and my iPhone with Strava going in my left pocket. The mileage was off by 1.5 mi. between the two. The track looked better for the GPS so I'm leaning toward the GPS being the correct one.

Next test: bring my old Garmin 305 on the ride as well. I'll probably get 3 completely different answers and be even more confused.


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## SoCal-Rider (May 25, 2009)

...and I sent an email to Baja Designs to get their thoughts. We'll see if they get back to me.


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## shiggy (Dec 19, 1998)

yfz_duner said:


> Jeez! Now I don't what to trust. I rode last night with my Garmin 500 in my right pocket and my iPhone with Strava going in my left pocket. The mileage was off by 1.5 mi. between the two. The track looked better for the GPS so I'm leaning toward the GPS being the correct one.
> 
> Next test: bring my old Garmin 305 on the ride as well. I'll probably get 3 completely different answers and be even more confused.


Yup, I bet you will. My Edge 305s have always given the most detailed tracks, followed the roads/trails the best, most consistent from ride to ride, and recorded the longest distances. The 800s I had we're the worst, the 200 nearly as bad. 2-3 miles different on a 17mile route.


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## Nutball (Oct 11, 2008)

I have a Baja Design Double Stryk and a Garmin Edge 500 (using the GSC-10 wheel sensor) and have never had any issues. Moreover, I mount the Garmin on my stem which makes it very close to the light head.

Like several other posters, I did have multiple issues (99 mph speeds, screen flickering, etc) with my previous HID light and one of my old cyclocomputers.


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## Harold (Dec 23, 2003)

Nutball said:


> I have a Baja Design Double Stryk and a Garmin Edge 500 (using the GSC-10 wheel sensor) and have never had any issues. Moreover, I mount the Garmin on my stem which makes it very close to the light head.
> 
> Like several other posters, I did have multiple issues (99 mph speeds, screen flickering, etc) with my previous HID light and one of my old cyclocomputers.


now this is interesting.

do you wrap the cable around the HS spacers like the OP? steel or aluminum steerer?


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## Nutball (Oct 11, 2008)

NateHawk said:


> now this is interesting.
> 
> do you wrap the cable around the HS spacers like the OP? steel or aluminum steerer?


No, I leave the cord slack (aluminum steerer). I used to route it under the stem but I had an incident where the cord got hung up on the stem and disconnected the light in the middle of a ride. The routing is a little nicer on my other bike (Jet 9) as the cord doesn't stick out since that frame permits better battery placement.


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## Harold (Dec 23, 2003)

OP, please report back.

I am wondering if the cable wrap might be the problem but we need you to run some tests.


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## Gundam168 (Dec 19, 2012)

yfz_duner said:


> This is a cross-post from the Lights forum. They said to post in here too.
> 
> Update to my original post over there: After a little more testing it's looking like it is the light causing the interference. I like having my time and mileage visible right in front of me on the GPS. Sucks I'll have to move it.
> 
> ...


What do you mean by *"around the time change"*.

Reason I asked is because when I was doing night rides between 11PM and 1AM, my GPS would *stop*(Update: corrected) tracking for about a few minutes during midnight. I was still on Endomondo using my 520 MHz Huawei smartphone GPS device. I brought up this issue to Endomondo CS and all I got from them was a wiseass "Cinderella" response. I just had a simple AAA battery operated LED flasher and a wired cyclometer.

Haven't been doing midnight rides lately and I've quit Endomondo. But I will check again maybe the next few nights.


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## SoCal-Rider (May 25, 2009)

I mean the switch from daylight savings time. I'm no longer able to get home from work and ride in daylight.



Gundam168 said:


> What do you mean by *"around the time change"*.
> 
> Reason I asked is because when I was doing night rides between 11PM and 1AM, my GPS would top tracking for about a few minutes during midnight. I was still on Endomondo using my 520 MHz Huawei smartphone GPS device. I brought up this issue to Endomondo CS and all I got from them was a wiseass "Cinderella" response. I just had a simple AAA battery operated LED flasher and a wired cyclometer.
> 
> Haven't been doing midnight rides lately and I've quit Endomondo. But I will check again maybe the next few nights.


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## SoCal-Rider (May 25, 2009)

So after my experimenting I'm 99% sure it's the light messing with the GPS. It sucks I can't run my GPS on the stem in my line of sight at night. Oh well. That's electronics for you.


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## Harold (Dec 23, 2003)

yfz_duner said:


> So after my experimenting I'm 99% sure it's the light messing with the GPS. It sucks I can't run my GPS on the stem in my line of sight at night. Oh well. That's electronics for you.


Did you try changing your cable routing to something like Nutball's? I am wondering about the possibility of your cable wrapped around the steerer (is it alu or steel?) inducing a magnetic field that is actually causing the GPS to act wonky. you also didn't say if you're using a wheel sensor or not. I would think that induction of a magnetic field on the steerer would be more likely to affect a wheel sensor than the GPS satellite signal, but I'm not an expert. I'm just thinking out loud.


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## SoCal-Rider (May 25, 2009)

I did try changing the cable routing from wrapping around the steerer to around my carbon frame. GPS track was still all wonky. 

No I don't have a wheel speed sensor. Just the Garmin 500.


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## Harold (Dec 23, 2003)

yfz_duner said:


> I did try changing the cable routing from wrapping around the steerer to around my carbon frame. GPS track was still all wonky.
> 
> No I don't have a wheel speed sensor. Just the Garmin 500.


can you post some example tracks?


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