Losing GPS Signal After Sometime…

11 thoughts on “Losing GPS Signal After Sometime…

  1. Hi,

     

     

     recently i am facing a strange problem, i lose the GPS signal after power up of  the modem,,,,,sometimes after 30 min and sometimes after a few hours.

     

    restarting the modem will solve the issue.

     

    could you please advice

     

    P.S. I am using the

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    GM862GPS731T022

    1. Tarek please give us more info:

      – GPS sw. version (AT$GPSSW)
      – GPS antenna characteristics (datasheet can help)
      – internal or external application (Python or external host)

      – NMEA sentences log showing the problem

      – include also GPS&antenna status AT$GPSAV, AT$GPSAI, AT$GPSP, AT$GPSPS

       

      Thanks!

       

  2. Hi Cosmin,

     

    sorry i was on business trip, i passed the information to the programmer please find below the answer.

     

     

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    AT$GPSAV?<CR>AT<CR><CR><LF>$GPSAV:3912<CR><LF><CR>OK<CR><LF>

     

    AT$GPSAI?<CR>AT<CR><CR><LF>$GPSAI:11<CR><LF><CR><LF>O<CR><LF>

     

    AT$GPSP?<CR>AT?<CR><CR><LF>$GPSP
    1<CR><LF><CR><LF>O<CR><LF>

     

    AT$GPSPS?<CR>AT?<CR><CR><LF>$GPSPS:
    0,1800<LF><CR><LF>OK<CR><LF>

     

    AT$GPSSW?<CR>AT?<CR><CR><LF>$GPSSW:
    GSW3.50Telit_.5.00.0-C23P2.0a <CR><LF>OK<CR><LF>

     

     

    we are developing our own hardware & software we are not
    using python.

     

    regarding the GPS Antenna we are using a generic one from
    the local market if you have any suggestions please advise…

     

     

    by the way we are able to get the GPS signal back by either
    restartnig the modem or resetting the parameters using the code below….

     


               
    ldi acc0,0

               
    sts UBRR0H,acc0

               
    ldi acc0,103

               
    out UBRR0L,acc0

               
    ldi acc0, (0<<USBS0)|(1<<UCSZ01)|(1<<UCSZ00)

               
    sts UCSR0C,acc0

     

               
    $PSRF100,1,38400,8,1,0*3D",13,10

     

               
    ldi acc0,0

               
    sts UBRR0H,acc0

               
    ldi acc0,12

               
    out UBRR0L,acc0

               
    ldi acc0, (0<<USBS0)|(1<<UCSZ01)|(1<<UCSZ00)

               
    sts UCSR0C,acc0

     

               
    $PSRF103,00,00,00,01*24",13,10

     

               
    $PSRF103,02,00,00,01*26",13,10

     

               
    $PSRF103,03,00,00,01*27",13,10

     

               
    $PSRF103,04,00,00,01*20",13,10

     

               
    $PSRF103,00,01,00,01*25",13,10

     

               
    $PSRF103,05,01,00,01*20",13,10

     


    1. Tarek, it is still not clear what do you mean with "I lose the GPS signal after power up".

       

      – Do you see a degradation of the GPS signal received or the NMEA sentences disapear?

       

      – Are you acquiring NMEA sentences from AT serial port with AT$GPSACP/ AT$GPSNMUN or GPS_NMEA port?

      1. Also if you have a chance to test other antennas as well, with a Telit EVK, just to be sure and validate the hardware, would be very helpful.

         

      2. HI Andrea,

         

        below are the answer from our R&D engineer.

         

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        Yes we are acquiring the following two NMEA sentences

         

        "$PSRF103,00,01,00,01*25",13,10

         

        "$PSRF103,05,01,00,01*20",13,10” from AT Serial Port….

         

        Every one second one NMEA sentence….

         

        Our problem is sometimes no reply from the Modem for the NMEA
        Sentence "$PSRF103,00,01,00,01*25",13,10….

         

         

        1. is there any reason to not enable GGA and VTG for a 1Hz constant output instead of polling them constantly?

          e.g.

          "$PSRF103,00,00,01,01*25",13,10

          "$PSRF103,05,00,01,01*20",13,10

  3. Are you 100% the string is not coming back, maybe is only skipped by your application for a reason? Ie try to read only the sentences in the other order; try to read only one sentence, try to read other 2 sentences, try to read the same from a PC etc.

    How often do you see the failure/missing answer?

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      I already thought and tested those things before…..and am
      sure 100% modem not giving any reply….but after resetting GPS am getting….

       

      For this missing there is no fixed interval…..anytime it occurs…

      1. Hi Tarek,

         

        does a repeating of the query "$PSRF103,00,01,00,01*25",13,10…." can fix the issue or does the GPS receiver stops to respond to any $PSRF query or command?

         

        Do you use AT$GPSR=x to reset the GPS? It could be that an hotstart with AT$GPSR=3 is enough to restart it without losing too much time.