Marine Electronics Forum - NMEA data ground?
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05-01-2011, 10:42 AM
I am installing an ICOM412, and interfacing with Raymarine 50D.
Instructions explain how to properly connect the leads, however, the leads from the Raymarine do not have data ground or shield wires.
Have never attempted to solder wires so small.
I see 3M has a nice quick connect, but have found that they are sold 100 per box....I need 2
NMEA +(red wire) to NMEA/DATA out
NMEA -(red wire shield) to NMEA/DATA ground(no shield on these leads)
05-01-2011, 11:07 AM
The NMEA connection on the A50D is the yellow wire which is your data + output and the brown wire is the data negative wire that is connected to your Icom input.
05-01-2011, 12:10 PM
NMEA in + (red wire) → NMEA / Data out
(red wire shield) → NMEA / Data ground
NMEA out + (white wire)
→ NMEA / Data in
NMEA out (white wire shield) → NMEA / Data ground
RAYMARINE told me:
ICOM RED to RAYMARINE YELLOW(data out)
ICOM WHITE to RAYMARINE GREEN(data in)
pos to pos, neg neg, data in to data out..understood.
BUT, the ICOM wires are a COAXIAL CABLE, the RAYMARINE leads are not.
See above ICOM table for my confusion
What is this DATA GROUND?
What is the purpose of a COAXIAL on a COAXIAL cable I guess???
Thank you very much for the reply
05-01-2011, 12:17 PM
The shield wire on the Icom is the negative data wire on your inputs and outputs.
05-01-2011, 12:36 PM
The yellow output wire from the A50 is connected to center conductor of the red wire on the Icom. The brown ground wire on the A50 is connected is connected to the shield wire of the red lead. It's not a pretty connection, but that's how they're paired.
05-01-2011, 12:40 PM
I think I get now
So splitting/seperating the coaxial wires from the ICOM will be necessary
05-01-2011, 12:46 PM
Yes, that is correct, the center conductor and the shield are wired to the A50 as separate leads.
05-01-2011, 12:52 PM
THANKS Team Rugby!
The Raymarine rep was questioning why there were only two leads coming from the ICOM.
I believe he was unaware that the ICOM leads are coaxial.
05-01-2011, 01:04 PM
To my knowledge, Icom is the only manufacturer of VHF's that uses coax for NMEA connections. The manual is not abundantly clear and the drawing is not all that good either on what you're supposed to do. I do a lot of installations and the first Icom I ever looked at was a bit of a head scratcher, so I know where you're coming from. Good luck.
05-01-2011, 02:42 PM
On a boat there is only one "ground" and that is the battery negative terminal. NMEA serial data signals can be either differential (balanced) or single-ended (unbalanced). It is typical that the NMEA OUTPUT signals are single ended and are referenced to the device chassis, which is typically tied to battery negative. It is typical that NMEA INPUT devices are differential or balanced devices. These devices have two inputs, a NON-INVERTING input that is often marked with a (+) and an INVERTING INPUT, often marked with a (-). The (+) and (-) are not polarity indicators.
The typical situation for connecting a single-ended OUTPUT to a differential INPUT is to connect the output conductor to the non-inverting input, and to connect the inverting input to battery negative.
It is rare to have a differential OUTPUT. If you do, in almost all cases the NON-INVERTED output, usually marked with a (+), is connected to the NON-INVERTING input. The INVERTED output, usually marked with a (-), is connected to the INVERTING input. If there is a single-ended input, you should not connect the INVERTED output to chassis.
Of course, this is much too much electrical nonsense for the average boater, and it is a shame. The manufacturers and their association, the National Marine Electronics Association (NMEA) have done a miserable job with all of this. If it took this much explanation and science to connect a mouse to a PC then 90-percent of PC's would not have a working mouse. For some reason NMEA and boat electronic manufacturers all think the typical boater is just an electrical engineer on his vacation. They should have engineered a solution to this so it was much simpler to interconnect devices.