Yes, sorry for the confusion. I am reffering to a small black square antenna located under the dash...not the square on the dash itself.

 

Most portable GPS units have an optional mag mount antenna that you can buy and stick on the roof of the vehicle for excellent performance. Since the freq are the same for the in-dash units, you can use one of these portable antennas. Just make sure there is an external antenna socket on your unit and that the connector is the same. Mount the external antenna somewhere on the roof where you can easily hide the wire and then route the wire into the vehicle through the firewall.

That's what I do for my street pilot. Works great.

 

So now that we know where it is, is there a secret menu in the nav system that will tell you information on how many satelites, and how strong their signals are?

There doesn't seem to be any point in getting an external antenna, changing the antenna, etc unless you can measure some difference.

 

Hi All

When I stated I was pretty sure that little square in the middle of the dash was a GPS antenna, it was a guess because the Workshop manual said it was behind the Nav unit. I have never removed the unit to check it out. There is no mention of two GPS antennas, but I found a Ford Patent in 2004 that discusses this issue. Here is part of that patent since this is the subject matter.

A method of measuring dynamic movement of a vehicle by employing multiple GPS satellites and determining velocity based change in the carrier frequency of multiple satellite signals. Two GPS receiving antennas and a controller for processing received GPS signals and monitoring a carrier frequency associated with the GPS signals. The controller determines a change in the carrier frequency of the GPS signals due to Doppler effect. The controller further determines a first inertial velocity vector of each of the receiving antennas based on the change in carrier frequency, and determines angular rate of the vehicle based on the inertial velocity vectors. The controller further determines vehicle longitudinal and lateral velocity and acceleration as a function of the inertial velocity vectors.

http://www.freepatentsonline.com/6671587.html

GaryG

 

Amazing that they could patent that. That's the way GPS works.

I read this thread because my (factory-installed) GPS just bit the dust (yesterday it put me in the middle of a lake, but I'm sure it was wrong), and I thought it might be something I had done to the antenna. Apparently not.

Anyway, has anyone else had the factory GPS leave the land of the living after about a year of loyal service?

Hal

 

When the in-dash system looses its satellites, it switches to something call "dead reckoning". With that, the Nav system will attempt to continue guiding you by roughly estimating your position based on your last GPS position, the direction you are traveling, and how fast you are going. I guess it could be rough enough, that enough error creeps in that you end up shown to be in the middle of a nearby lake.

I know that my hand-held Garmin will just stop guiding you, and state "satellite signal lost".

Have you tried it again today?

 

Oh yes, it's been doing this for a week, so it's a real problem. It isn't a complete system failure, it just puts me where I am not, like under water.

As for dead reckoning, all good tracking systems use it, and mariners have been doing it for millennia. During WW II our radar systems had it, since the Japanese aircraft would otherwise fly behind a ship, blocking the signal. With an extrapolated track (dead reckoning) we were able to pick them up as they came out of the radar shadow.

Thanks,
Hal

 

I've had this happen twice in 2 years. Always goes back to normal.

I attribute it to environmental conditions, and/or poor satellite geometry, by law of averages, happens once in a while.

Are there any nuclear tests going on in your area, or does your neighbor use HAM radio? While probably not, there could be 1000 other activies we haven't thought of causing "interference".

 

I've had it happen once where it thought I got on a highway when I was about 1/2 mile away. It took about 5-10 minutes to actually figure out where I was. I think it got confused at the on-ramp and lost the signal on the underpass. I think if you eject the disc or turn off the unit it may re-locate your position. If not, you can try either disconnecting the battery cable for a few minutes to "hard" reset the system or pull out the unit and unplug the power harness from the back for a few minutes.

 

Knock on wood..... 3 TIMES IN 2 YEARS.....

Just tonite my GPS moving map was 1/2 mile to 1 mile off of my actual position. Happend at 7pm out in the open country with clear views of the skies, then I tried again at 10pm in Denver's downtown with the same result.
By 1am it was back to being very accurate.

Let's not discount the fact that the U.S. Government, wholly responsible for the GPS system can perform experiments, upgrades, downgrades, calibrations, and "selective availability" at any time, without notice. In times of war or national security, it (GPS) can be disabled at any time. I'm not saying that is the cause tonite, but it is very possible.