Dave Burrows – Tech / iPhone Blog – Technical Evangelist

There’s a number of things that can affect a bad GPS fix.

• You started your journey without a good quality GPS fix and the iPhone is trying to always ‘catch up’
• You might have an Athermic UV coated Windscreen in your car which dampens radio signals (of which GPS is one of these)
• You might have your heater coil in your windscreen on, and this is sending a small electrical current through the windscreen to keep it from freezing / misting up and this is dampening GPS signals
• You might be unlucky to be driving through an area such as an ‘urban canyon’ which has tall buildings either side of you blocking the GPS signals
• You might be unlucky to be driving through a lot of heavy tree cover blocking GPS signals
• Where you position your device on the windscreen can affect the GPS coverage.  Always ensure it has a good clear view of the sky as close to the windscreen the better
• Heavy cloud cover, rain, snow can affect GPS coverage
• Ionosphere disruption around the earth can also affect GPS coverage

I’ve known all of the above can block your GPS coverage for 10 or so years, but this past week I’ve started to receive very bad GPS signals across all applications that I’ve been using on the iPhone, and I’ve really been scratching my head to work out what was causing it.  Some days it’s fine and some days it’s…. to put it mildly…..Terrible!

Nothing has changed, I’m driving the same car, under the same conditions and the same routes.  I’m using the same iPhone, it’s mounted in the same place on the windscreen, I wait to get a fix before I start driving.  So what has changed other than the weather getting slightly more colder and cloudier?

This weekend I finally found out what was causing the problem.  Now not wanting to keep you all in suspense, but this in hind sight is quite an obvious thing that I haven’t really thought much about in the past…..

This past week I’ve been driving with a case on my iPhone!   I’ve been using the Switch Easy case for some time now, but usually take the case off when I get in the vehicle.  I didn’t think that it fitted in the car-mount that well, but since finding a slightly wider car mount, I’ve been driving with it on for the past week.

I carried out a drive this weekend with the case on and got less than par GPS signal coverage (e.g. lots of GPS fix loss and snapping me to side roads as if the GPS fix quality was sub-par).  Taking the case off and driving the same trip again, I had no problems at all.

This is by no means a conclusive test or an ultimate fix, and I will be carrying out more testing with and without the case over the course of the next few weeks.  If you think about it the GPS receiver is in-built into the iPhone and near the back case, so if you’re adding more plastic/rubber to the back of your iPhone then there’s more chance of dampening GPS signals.  

If you are experiencing GPS problems and have a case on your iPhone, perhaps try taking it off whilst you are in-car and see if this improves your GPS quality and please let me know your experiences!

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