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  1. #1
    Good Citizen
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    Default No Signal on GPS

    Today my GPS took more than 20 minutes to acquire satellites. It really sucks when you're in a rush to get somewhere unfamiliar. So I drove around like an idiot until I got a signal. Any of you had this happened before?

  2. #2
    Speed Demon
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    road conditions? lotsa buildings or what? what kind of gps?, what chip does it have?, cold start?(meaning after sitting in a car all night?), how old?

    lotsa questions before i can even consider an answer

  3. #3
    Captain Insano
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    Quote Originally Posted by VicRod74 View Post
    Today my GPS took more than 20 minutes to acquire satellites. It really sucks when you're in a rush to get somewhere unfamiliar. So I drove around like an idiot until I got a signal. Any of you had this happened before?
    This can happen if all of these conditions are met: Your GPS antenna doesn't have a clear view of the sky, it was a "cold start" for your GPS unit, and you started driving immediately. One of the fastest "cold start" GPS acquisition times is found in the Jupiter 30 GPS chip set. Cold start refers to the GPS chip set being completely powered off and not retaining any ephemeris data for where the GPS satellites are currently located in orbit. Even so, the minimum "cold start" signal acquisition time for the Jupiter 30 is listed in the tech sheet on Navman's web site as "42 seconds."

  4. #4
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    Default

    make sure that the detector is mounted low on the windshield so it can see the sky. If you are high the roof will block the antenna


    Quote Originally Posted by VicRod74 View Post
    Today my GPS took more than 20 minutes to acquire satellites. It really sucks when you're in a rush to get somewhere unfamiliar. So I drove around like an idiot until I got a signal. Any of you had this happened before?
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  5. #5
    Power User
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    Cause of delay may be due to the following:


    "The GPS requires the current time, the orbital position of the satellite and a measurement of signal delay. Calculating accurate co-ordinates of an object primarily depends on three data . To measure the signal delay, the receiver prepares an identical sequence of the Coarse-acquisition (C/A) code and compares it with the sequence received from the satellite. The changes in bit transition can be calculated an approx. of 10 nanoseconds for the code. As the signal travels at a speed equal to the light, the net error can be taken as 3 meters.[/color]
    However, there are several factors that affect directly to the accuracy of the GPS signal and some of them are given bellow.

    Atmospheric effect – Any change in atmospheric condition can affect GPS radio signals as signals travel through the thick layer of the atmosphere. Both ionosphere and troposphere can leave little or more impact on the speed of the radio signals. Dual frequency measurement or comparing the two frequencies L1 and L2 can reduce the error and also define a precise location of the receiver.

    Multipath effects
    – This occurs when signals are get reflected or bounced by coming in contact with surrounding hills, buildings or any kind of hard core object before it reaches the receiver. Thus, increase in travel time of signals cause error. However, with the help of the technique named narrow collector spacing the receiver recognizes the long delay signals and does not take into account while calculating the precise time and location. Also there are some specialized antennas are used to measure the exact data from the signals that are slightly deviated or delayed. But it’s a bit difficult as the fluctuation is very little in atmospheric delay.
    Receiver clock error – The receiver enabled with a clock that is not as accurate as the clock in satellite and so produce a little timing error.

    Orbital error
    – This occurs when the satellite’s orbital location is calculated wrongly. As the right location of the satellites position in the orbit is essential, even a small error can leave a large difference as far as accuracy is concerned.

    Satellite geometry
    - It is the exact position of the satellite at a given period of time. Ideally when satellites are located in wide angles from each other, it becomes easy to measure distance. However, poor satellite geometry occurs when they are in a line or in a tight grouping. [/color]
    Artificial degradation of the satellite signal – The Department of Defense of US recently restricted certain highly accurate GPS signals (military related) from public use as these can be misused and so intentionally degraded. This is called Selective Availability (SA) in which kinds of intentional errors like creating noise in the satellite clock or transmitting some false orbital data to the satellite that can come back to the receiver at the ground. However, receivers of Defense Department have the capability of rectifying those errors."
    Last edited by KnightHawk; 07-07-2008 at 10:31 PM.

  6. #6
    Yoda of Radar
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    I think the biggest problem is when people have a 'Cold start' AND drive immediately after it is turned on... when you turn on your GPS, wait there for a minute or two before you start driving (I wait until it catches signal), especially if your driving in the city where large buildings may make the reception intermittent.



    I live out in the boonies so there is not much to interfere, and with a cold start and staying still (Not driving): I normally get signal within ~1minute. (Normally just over, but sometimes less, its really give or take). If I drive I have noticed It can take upwards of 3/4 minutes or so.

  7. #7
    Scratonicity Groupie
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    I got tired of my garmin nuvi 350 doing this. So now that I've got the TT 920T, I just do a quick sync before I head out the door, and it's got the sats locked and ready as soon as I turn it on

  8. #8
    Yoda of Radar
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    Quote Originally Posted by thestaton View Post
    I got tired of my garmin nuvi 350 doing this. So now that I've got the TT 920T, I just do a quick sync before I head out the door, and it's got the sats locked and ready as soon as I turn it on
    Thats odd... my Cheaper nuvi 200W has never had a problem.



    Just this morning it obtained a 3 bar (green) signal when I was on the floor-level of a parking garage... I was at a docs appoint.

  9. #9
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  10. #10
    Scratonicity Groupie
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    He's the happya$$ of GPS units

 

 
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