GPS Start / Finish Line help

[FoxSTI]

Guys, I have setup a "Fake" start finish line down the street from where I keep my car just to test the system a few weeks ago. I drove through it several times and it seems to work fine.

however, I noticed that from time to time that my times will register me driving through the "start line" although I really haven't. Yes I am in close proximity but did not cross it. I am going to be taking the car to the track next weekend for the first time since installing my Motec dash. I would like to have it work properly. Should I maybe set the "detection" radius to a smaller distance?

Thanks

[David Ferguson]

My advice is that a detection radius between 20 - 80 feet (6 - 25 meters) works well at most car tracks.

If you are getting odd lap times, check your settings under Calculations->Lap Time & Number... -> Lap Time tab,

[adrian]

When you say close proximity, how close exactly?

Do you have some data logging showing this happen that you could send through?

[FoxSTI]

I do not have a log. But earlier this week I purposely drove by my S/F line when leaving. then all the sudden my laptimer registered a lap count and time in a different part of town aprox 10 miles or more.

The GPS antenna is inside the car getting exposure via the back window. I ideally I think I would want it inside the car, or am I wrong? what is going to be the best place?

[adrian]

Having the GPS antenna inside the car is not ideal. This could be part of the problem as the accuracy of your position may not be very good. The best place to mount a GPS antenna is always on the roof and as far from any other antennas as possible.

[FoxSTI]

I am not sure... today I drove away from the S/F line. about 4 miles away, the GPS thought it had crossed it and it started the timer. I have an event this friday (yes friday). Its going to suck is this very expensive device doesn't time my laps properly.. =(

[adrian]

It is a bit hard to work out what is going on without any logging.

How many Satellites is the GPS seeing? What values do you get for the DOP channels?

Having it in the back window is never very good, especially if it has a rear demister, which I assume it does being a road car.

[FoxSTI]

I will trouble shoot tomorow and report.
I need to find a way to put the GPS on the roof, at the center line of the car right above the windshield. OR,
maybe on the dash (so it doesn't get stolen or something) I would love to see where people are putting their GPS on their track cars.

[the_bluester]

My previous (non MoTec) dash I had the gps on the trim at the front of my cars dash (which was metal so it stayed put) and I did not see any reception issues. It would have been easier to externally mount as the receiver was in the dash and the external part was only an antenna on a flying lead with a small connector on the end.

[FoxSTI]

yeah with a "tin roof" car, I would probably have a wire coming out the side of the door somewhere. not ideal.