I am having issues with my autopilot (Comnav Commander) declaring “Invalid Heading” from my NMEA 0183 GPS compass (1st gen Comnav G2) . The errors are sporadic with no clear pattern. My navigation computer (Surface Pro 7) running CE also receives its heading from the GPS compass via a NMEA multiplexor (Actisense NDC-4) that adds the AIS data. When I am having a period of the “Invalid Heading” messages from the AP, I look at the data stream of NMEA 0183 messages coming into CE on the “Electronics” tab. I see nothing out of the ordinary in that data stream and the heading data shown in CE looks normal.
I am wondering whether I am getting checksum errors in the NMEA 0183 HDT sentence which causes the AP to alarm. How does CE handle a checksum error in a NMEA 0183 sentence? Does CE ignore it, log it anywhere or flag a warning?
Sentences with invalid checksums (or other problems) are silently ignored by Coastal Explorer.
Showing problems like this on the port page is on our to-do list, but has been at a pretty low priority. There is a feature that could help you determine if a checksum is correct, though. NMEA 0183 talker port pages have a “Send an NMEA 0183 Sentence” box on them. You can type one of the suspicious sentences into the box but leave off the checksum. Coastal Explorer will display the full sentence with the correct checksum next to the Send button.