[TG] [TG11] ST5000+. NO DATA error.

[Tom - Raymarine - Moderator]

Hello davenz,

Do you know that what the NMEA mux is transmitting is exactly (character for character) what iSailor is sending? If so, it would be good to attach one of those NMEA logs.

Some common problems with NMEA0183 data:

• Voltage tolerances. Signalling voltage levels have changed with later revisions of the 0183 spec and older devices tend to be less sensitive to lower signalling voltage levels than newer ones.
• Single-ended versus differential signalling. 'Modern' (ha ha) NMEA0183 is differential, that is voltage is applied positively to one wire and negatively to the other and the signal must be measured as the difference between the two, whereas older devices use/expect a single transmitting wire and a common (0V) reference potential. The ST5000+ is old-style non-diff. What does the mux use?
• many NMEA0183-ish devices use NMEA0183-formatted data over the RS232 electrical signalling layer, which is not strictly 0183 compliant.
• data content: is everything the pilot needs there, and are the Data Valid (A, V) flags present and correct?
• checksums - must be present and correct
• ... I'm sure there are some more I've forgotten from my days handling 0183 regularly.
  

To really see what's happening, you would need to read what was coming into the ST5000+ with a PC and serial terminal (I use Teraterm on Windows or Moserial or Cutecom on Linux) and check the signalling with an oscilloscope.

What the pilot needs to see will be at least bearing-to-waypoint, distance-to-waypoint and cross-track error (later pilots also need waypoint name.) These can come from any combination of the supported NMEA0183 messages which you will find in the ST5000+ handbook. RMB should provide all that's required as long as all fields are present and valid.

Regards,
Tom