Hi Ian, I tested an early B400 in 2017 and had similar troubles. Here's part of what I reported to EmTrak at the time:

"When I installed the B400 on my boat's main N2K network, it could see three Heading sources, but only use one without generating a invalid heading error. The successful source is a True Heading Compact satellite compass (a Hemisphere now sold by Si-Tex, Navico and others). Rejected were a Lars Thrane LT-500 and Airmar PB200, both of which display True Heading on multiple displays. I'll do more experimentation soon, and I can log the PGNs in the network, but I have not seen other Class B transponders as fussy about Heading source."

Eventually they said they had a software fix for this (though I never tried to decipher the PGNs coming from the various heading devices) but it could only be applied to my early unit at the factory. So I didn't try the fix and the B400 was returned. However, I have a SiTex MDA-5 Class B/SO testing on my boat now -- made by SRT like the B400 is -- and it's working fine even though the satellite compass is no longer installed. It doesn't have its own display but its output is displayed without problem on various MFDs and to apps via WiFi.

This is a confusing area as I didn't even think that Class B transcievers or AIS displays were required to have Heading input, though maybe that changed (and having it is a good thing). Also the current B400 manual shows supported NMNEA 2000 input as "PGN 127250 Vessel Heading" or "HDT" via 0183. There's no mention of THS except in the abbreviation list.

Meanwhile, NMEA defines 127250 thusly: "Heading sensor value with a flag for True or Magnetic. If the sensor value is Magnetic, the deviation field can be used to produce a Magnetic heading, and the variation field can be used to correct the Magnetic heading to produce a True heading."

Hopefully other readers can shed some light on all this, and I may have a chance soon to see what my various Heading sensors are actually putting into their 127250 PGN (though maybe you're using NMEA 0183?)

127250

Thanks Ben for your quick response.

i have had various issues with the B400 all of which have now been resolved with this one exception. As you say, it seems incredibly fussy over what heading source it receives, and frankly I have not had great experience with Em-Trak when it comes to resolving issues.

I understand that my Airmar H2183 can be configured to output HDT, although it is not set up at the factory to do so. I have just ordered the Airmar 0183 to USB converter which hopefully will allow me to change the configuration of the H2183 through the Weatherstation program.

I have found the B400 functions without the heading input when underway but I get the constant “no heading input” warnings, and when stationary it looses orientation.

I guess I’ll try the H2183 re configure and see how that works out.

My previous boat I had fully equipped from New with a full Furuno navigation suite, all NMEA 2000 based. Having somehow got bitten by the Classic Boat Bug I sold that N47. Now my current boat is a 72 ft 1948 Wood Motoryacht that was re-fit in 2001 with a NMEA 0183 based system. I have considered replacing all the kit with new, but as the existing kit works fine I’ve elected to struggle with the 0183 learning curve!