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Poor GPS Reception with Certain Car Windshields

Oct
6
2006

I’ve had a few conversations with people recently who were experiencing trouble getting good GPS signal quality in their vehicles. In one case the GPS was new and it was the first time they had used a GPS receiver. Another reader asked why their trusty GPS suddenly didn’t have god reception and their backup GPS suddenly didn’t have good reception either. In both cases it ended up being something about the vehicle that was causing the issue.

Let’s talk just a little bit about how GPS works. Think of your GPS receiver as a little FM radio. The GPS satellites send signals that your GPS receiver can listen to. In fact, the frequency that GPS signals are broadcast over are on a frequency simlar to that of FM radio (1200 MHz and 1500 MHz areas). Anything that might disturb good reception over FM radio can also cause signal issues for GPS receivers.

It turns out that both of our readers were in vehicles where the FM antenna was built into the windshield. In one case the car was new to the reader and thus they didn’t notice that the poor reception had started when they started driving the newer vehicle. In the other case the driver was finding that the GPS could only pickup a good signal when on either side of the dashboard; when it was in the middle it was under the FM antenna and they had a difficult time getting a solid GPS signal.

I’ve also heard sporadic reports that certain tinted windshields can interfere with GPS reception although I haven’t been able to see this happening with my own eyes. So the type of car you drive (or more specifically the type of windshield you have) can interfere with the GPS signal. If your vehicle has a windshield with an integrated FM antenna you might need to locate the GPS receiver away from where the FM antenna is located to get good reception. I even heard from one reader who said their FM radio would no longer work when they turned on the GPS.

6 Responses


  1. Wow…great article! Makes me realize that GPS units that offer an external antenna option may be the way to go(I believe trunk lip-mounted antenna are pretty much the norm).

    Here’s another great reason why I check your website regularly…..great info like this! Keep up the great work. Consumers like me greatly appreciate what you do!

    Stever
    Mesa, AZ

    Stever - October 8th, 2006
  2. Thanks, for the comments, Stever. Yes, sometimes an external antenna option is the way to go. I know a few people who have routed external antennas to other parts of their car to avoid the FM antenna integrated into the windshield.

    Tim - October 8th, 2006
  3. I travel on trains in Germany, and sometimes use my GPS to know when I am closest to a destination, so I can exit the train at the nearest train station.

    Only sometimes can i get any GPS signals at all, even with a curved semi-overhead window ( I always hold the GPS unit directly by the window, with a large window also on the other side ).

    Possible that some of these train windows are double-pane glass or something ? It is surprisingly difficult to find info on reception through clear glass, even on the USAF’s technical GPS specs website. Feedback ?

    Steffen - June 1st, 2007
  4. Steffen, it is certainly possible there is something in the glass of the train that is blocking the GPS signal. What GPS receiver are you using?

    Tim - June 1st, 2007
  5. Hi thanks for your reply.

    I have both a Garmin Etrex ( the simple yellow one without maps ),
    and also a Garmin GPS III Plus, both behave the same way.

    These are double decker trains in Germany, I sit in the upper deck under a curved window to the side and partially overhead.

    Never a problem through auto windshield.

    About 30% of the time I get lucky and it gets a fix.

    I have also first booted up the GPS first outside on the train platform, got a fix, then immediately went into the train to a window. Usually loses the satellites.

    Annoying because i get coordinates of places I want to go from internet, then want to use the GPS to know when I am closest, to exit at the next station.

    Steffen - June 2nd, 2007
  6. I know a few people who have routed external antennas to other parts of their car to avoid the FM antenna integrated into the windshield. I believe trunk lip-mounted antenna are pretty much the norm.

    Stacey - October 21st, 2010



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