GPSgraf Problems and Solutions

1. GPSgraf is running but the SkyPlot window does not show satellites.
    
   • Look at the message window right-hand column. If a string of "gibberish" goes across the entire column, followed by many rows of cryptic messages, then everything is working OK. It can take several minutes before the satellite tracks are plotted.
   • Another check is go to "Serial Port Test" Menu and click "Test GPS Board. " Look at the message window right-hand column and watch for "SUCCESS! GPSboard recognized at baud=4800" message. If this message appears everything is working ok.
   • If no strings of "gibberish" are seen or the GPS Board Test results are "GPSboard not recognized" for bauds of 1200, 2400, 4800, or 9600 there is a problem. Check the following:
      
     1. All the GPS hardware connections. See the "Connecting the Garmin GPS II+ Receiver" section.
     2. The GPS receiver data output is connected to the serial modem port or the Stealth serial port
     3. The GPS receiver's "Interface" setting is "NMEA/NMEA 4800 Baud." See the "Garmin GPS II+ Receiver Setup" section
     4. The GPS antenna is connected to the receiver and has a clear unobstructed view of the sky, including the horizon.
     5. The GPS antenna cable has not exceeded the recommended length of 80 feet.
     6. The GPS receiver has been initialized and is reading satellites. Sometimes the GPS receiver will lose the satellite constellation and will need to be reinitialized (there should be a flashing message on the GPS receiver display screen indicating the receiver has lost the satellites). Follow the "INITIALIZING THE RECEIVER" procedure outlined in the owners manual.
         
2. GPSgraf "crashes" when starting up or when SeismoGraf starts up.
    
   • Check the Macintosh Clock. If time is off by a second or more reset the Mac clock manually. See the "Setting the Mac Clock" secton.
   • Increase the memory allocation of the GPSgraf and SeismoGraf software. See "Installing the SeismoGraf System Software" section.
   • The Ohio Seismic Network has found that starting GPSgraf before Seismograf avoids some crashes. After GPSgraf has locked onto satellites and displays them in SkyPlot wait 5 minutes or so allowing GPSgraf to correct and stabilize the Mac clock before running Seismograf. If the Mac clock is not precisely synchronized with the GPS clock, starting Seismograf will crash the software. GPSgraf makes time corrections in small increments, so, if the time differential is on the "large" side adjusting the Mac clock will take awhile.
      
3. GPSgraf and SeismoGraf consistently loses time lock.
   
   • The Ohio Seismic Network has experienced problems with the clocks on Macintosh G4 computers. The time on these clocks tend to drift severely with a drift rate that is greater than GPSgraf can correct for it. Thus, keeping time lock is near impossible. One solution that has worked is having the Mac clock connected to a Network Time Server. If the computer, however, is behind a "firewall" this solution will not work. To use a Network Time Server do the following:
     
     1. Go to the "Date & Time" control panel.
     2. Check the "Use a Network Time Server."
     3. Click "Server Options."
     4. Choose a time server from the drop down list.
     5. Select, under "Update the Time", "automatically, when the system clock is different from the time server."
     6. Click "Set Time Now."
     7. Click "OK."
   • The GPS antenna may have an obstructed view of the sky. Sometimes the GPS receiver will lose the satellite constellation because of nearby obstructions or the satellites are low on the horizon (there should be a flashing message on the GPS receiver display screen indicating the receiver has lost the satellites). Follow the "INITIALIZING THE RECEIVER" procedure outlined in the owners manual.

Last update March 17, 2003
Ohio Seismic Network   http://www.dnr.state.oh.us/OhioSeis