OK, I've read a little and understand we have NMEA listener devices and NMEA talker devices, and some that do both. Transmit on a talker must go to receive on the listener so you can't just hook all the transmit wires in one bundle and the recieve in another. There are at least three conductors needed if a device does both listening & talking (receive, transmit, and ground). Their ground looks to be seperate from the negative power grounds on the devices and my VHF has seperate grounds for receive and transmit.

I have a Standard Horizon chart plotter (with 2 sets of receive-transmit wires), a JRC Radar, a Standard Horizon VHF, and a Humming Bird depth, speed log and am left scratching my head as what is the best way to wire it all together.

It seems I might need a multiplexor.

Any links to a good treatise on wiring NMEA out there?

I am pretty sure I tied the ground of my Apelco sounder/nav device to power ground. It listens to position info being fed by a Navman chart plotter. What I think you may wish to do is have your depth sounder talk to the chart plotter for starters. Does the radar feed info or does it ingest data from another unit such as the chart plotter? If that's the case, feed it the output (xmit) from the chart plotter.

I also assume that the VHF has a DSC (digital calling) feature that will take position info and automatically broadcast it in case of emergency. That would be the only reason to tie it to another instrument. I am guessing (only a guess) that you could feed it from the charting device (which is also feeding the radar). Standard Horizon should be able to confirm that or suggest a multiplexer.

(I just checked out Standard Horizon's site and looked at one manual (don't know which unit you have) and it appears to be able to handle more than one interconnection)

I assume you have a lot of the NMEA 183 devices (Rs-422) serial bus stuff. Buy the Opto-isolated version. see the noland stuff at nolandeng.com or http://www.navstore.com/detail.aspx?ID=1812 or Actisense http://www.navstore.com/detail.aspx?ID=1819 - Muxes and autoswitches handle the combining of data sources (multiple talkers). A Mux is needed to resolve data collisions. You some times need a buffer as the data rate is so slow (38K max) and talky. Noland makes a product for legacy (can adapt Chrylser) engines sensors to NMEA 183 (about 500 apiece). http://nolandeng.com/downloads/VS52man.pdf


This NMEA 183 stuff is subject to a lot of interference so install it without ground loops (OptoIsolate). It's easy to do and easy to screw up. Pain to find the problems unless a (you're me) and have a killer scopes (well 5) and PC com tools.

Joe, You might want to adapt part of it to NMEA 2000. For that use http://www.navstore.com/detail.aspx?ID=1631. A hybrid system may give you some nice options (rudder angle, fuel flow). Sorry to be late to respond. For NMEA 2000 Goto the Maretron site, and to SIMRAD and so does Actisense for info. The wiring is simpler than it seems.

There is no really good NMEA 2000 for dummies book yet (some of the Marine Electronics stuff bites also, but you can use COM port knowledge to figure it out (Optoisolate). NMEA 2000 is a bus architecture (sort like ethernet). (Devices negotiate taking turns as Talkers). They have specific addresses and a specific priority scheme. Compliant talkers (when configured correctly) take turns. NMEA is a CAN BUS not unlike (in fact very like) the one in your 2007 or later car - SAE J1939.