GPS/NMEA Trouble Shooting

There are a number of reasons why Navmaster may be unable to receive data from GPS or any NMEA output device, and you need to carry out several checks to locate your specific problem.

Initial Action

1. Ensure the NMEA cable is firmly plugged into the COM port (serial port) on the PC. If you have more than one serial port, the NMEA cable should be plugged into COM1, the default for Navmaster. In Windows XP, you can check your available ports from System Properties (press Windows Key + Break), Hardware Tab, Device Manager/Ports.
   If you have a USB/serial converter, see USB/Serial converter issues below.
   
   
2. In Navmaster select the Monitor side panel. If the top of the panel is blank or <NMEA inactive> is shown in blue, data is not being received at the selected COM port. If you have more than one COM port, check which one is selected from the Navigator/Options/GPS menu. Navmaster by default uses COM1. If DR is shown in red, Navmaster has switched to Dead Reckoning mode in the absence of valid positional data.
   

   Checking for data in Navmaster and independently of Navmaster

3. Open Navigator/NMEA Window/COM x Receive. This will display any data being received. If the window is blank or the data frozen, there is no connection.
   
   
4. Close Navmaster and check via Windows HyperTerminal. With your NMEA cable connected to GPS, go to Start\Programs\Accessories\ Communications\ Hyperterminal. Double click Hypertrm.exe to start the program. When prompted for a 'Connection Description' type "Test". When prompted for 'Connect to' select Direct to COM1 (or appropriate port for testing). When prompted for 'COM1 Properties' set Bits per second to 4800 and click OK.
   You should now see a stream of text messages on the screen, each line beginning with a $. The lines will probably start repeating after a few seconds.
   If nothing appears on screen, the problem almost certainly lies in your serial port allocation, in which case check your other COM ports via HyperTerminal until you locate where data is being received. If the text is garbled, the usual reason is that the baud rate is wrongly set - it should be 4800. If no data is coming into any COM port, there is a problem in the connection to GPS.
   
   
5. A common cause of NMEA data not being received by Navmaster is that your serial or USB port is already allocated to another application. Since Navmaster by default uses COM1, if you have other applications installed that also use COM1, no NMEA data will be available to Navmaster. Typical examples of other applications that might be set to COM 1 are: modems, weatherfax, programs like "Autoroute" which also use NMEA data. You can find out if COM 1 is 'busy' from Navigator/Option/GPS, where only available (free) COM port(s) will be shown under the COM Port, Receive combo box. If COM 1 is not listed, then it is busy.
   If your PC has a single serial port, you will need to re-configure your other application to run on COM2 or COM4, so that Navmaster can use COM1. If you have more than one serial port, you can set Navmaster to another port: go to Navigator\Options\GPS tab. Arrow down the COM Port, Receive combo box and select another COM port for Navmaster to receive GPS signals.
   
   
6. Another possibility is that your COM1 may have been configured for use with infrared devices (such as an infra-red printer). You will need to re-configure the infra-red device. Choose Settings from Windows Start menu, and select Control Panel. Double-click on Infra Red. Select the Options tab. If the infra-red COM port conflicts with Navmaster, change it to another port. Or if you don't use it, disable it entirely by unchecking all boxes.

   Other checks

7. Check that the necessary NMEA sentence output has not been 'switched off' at the GPS.
   
   
8. The baud rate may be incorrect at the GPS. Baud rate should normally be set to 4800 (the exception is AIS which needs 38,400).
   
   
9. Your GPS data may not be in NMEA 0183 format (eg "Seatalk"). You will need a NMEA converter unit to convert the manufacturer's proprietary format into the universal NMEA 0183 format. Please check with your GPS manufacturer.
   
   
10. Do you have more than one device connected to your GPS output? This can reduce the signal level available to the computer.
    
    
11. Incorrect wiring. See Appendix F of the User Guide, "NMEA Cable Installation".
    
    
12. Select the Satellite tab on the Monitor panel (press F9). If information is being received from the GPS, a quality indicator and the number of satellites in use will be shown. This may be below the level necessary for valid position information.
    
    
13. If data is still not being received correctly, and the above have been checked and are correct, disable any power-saving features used by the computer.

    USB/serial converter issues

14. If using a handheld GPS, check that the handheld is actually outputting data. It may not do so if you are inside a building (poor reception), or if in "Simulate mode", or with "NMEA out" inactive.
    
    
15. If your GPS is receiving & outputting data, go to Windows Control Panel, System, Hardware, Device manager, expand Ports and identify which ports have been added by the USB-serial converter (there will be a list).
    
    
16. In Navmaster allocate each port in turn to Navmaster to check the data stream. If you cannot see data coming in to any port, then you should close Navmaster and run Hyperterminal on each port to see if there is any data coming in to the PC. See Point 4 above for how to use Hyperterminal.

    Talker IDs

    Data from marine instruments are prefixed by Talker IDs which identify data type. Talker IDs are the second and third characters of each sentence (the first character is always $). By default Navmaster reads the standard IDs for each instrument type, eg GP for GPS, WI for Wind. Non-standard or proprietary IDs can be added so that if Gyro or compass data is channelled through the GPS and is prefixed by GP rather than HE (for heading), Navmaster can read the non-standard prefix. Another example is where data is fed via an integrated instrument system, whereupon 'II' will precede GPS data.
    To identify what data is coming in, a COM port diagnostic program is included on the PC Maritime CD in D:\ Diagnosics\ MTTTY.exe. Copy the MTTTY program to C:\Program Files. Then right mouse click on MTTTY.exe and select Send to Desktop (create shortcut). Click on the MTTTY icon on your desktop. In the MTTTY program select the COM port you wish to test and the baud rate, usually 4800. Select File\ Connect and NMEA data should be visible on screen. Select File\ Disconnect to stop the data and now you can identify the Talker IDs present.
    
    To add Talker IDs In Navmaster go to Navigator\Options \NMEA tab and select the Sentences tab. Select instrument type from the drop down list (ARPA, Autopilot, GPS etc). Click the New button (). A blank entry box will appear. Type the required ID and press Enter, then OK. Choose Workspace from the File menu and click Save so that your settings will be remembered. IDs can be deleted by highlighting an ID and clicking the Delete button.
    Connect your NMEA device which should now be able to display the appropriate output.