Wiring VHF w/ DSC to Garmin 740S

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localboy

New member
Trying to clean up some wiring and hook things up that have been lagging. I have a ICOM M304 VHF w/ DSC. Trying to hook up the DSC to a Garmin 740S. Here's the question:

ICOM instructions has yellow wire that says "NMEA IN (+)" and a green wire that says "NMEA IN (-)".

GARMIN's instructions do not say (+) or (-). They say "NMEA 0183 Tx (out)" and "NMEA 0183 Rx (in)". There are two sets of the same; just labeled port 1 and port 2.


So what wire attaches where?


:?
 
Well, the Garmin 740s has a prefix of GPSMap, so I would think that you want to connect the GPS data to your VHF radio, so that when you panic and hit the RED button, the rescuers will know from whence you panicked.

So, you want the data OUT of the Garmin, IN to the radio. I'd connect Garmin NMEA 0183 Tx (out) to VHF NMEA IN (+).

Looking at the Garmin 740 installation manual (page 5) the NMEA Tx wire, (blue in the manual) goes to the Rx in the radio. The Garmin uses the power ground as the low/return line, so make sure you're grounding the units to the same point.

Let us know how it works out.

Boris
 
The Garmin uses the power ground as the low/return line, so make sure you're grounding the units to the same point.
Click to expand...

So Boris, if I'm understanding correctly, the NMEA IN (-) on the Icom radio is the ground you're referring to above. I attach the Icom NMEA IN (-) to the ground buss that the Garmin is attached to. Correct? :?
 
When you get ready to use, you probably will have to set the com port of the Garmin properly. (I hooked mine up to SH and Uniden radios), The NMEA 0183 for the position to the radio, high speed AIS in to the Garmin. I used the ground as the common point.
 
Well, you're trying to interface 2 different manufactures, which is always a problem trying to figure out what is what.

Apparently the Garmin uses a single ended line for transferring NMEA data and uses power ground as a reference. Since the ICOM radio has a diffferential input (+ and -) for NMEA data INPUT, try leaving the GREEN line floating and see if that works. If not, and I'm betting not, hook the GREEN lead to power ground (not chassis ground.)

Standards is standards, and everybody translates them different.

I found an article that shows the above with pictures: Garmin output to ICOM input. So the GREEN line is connected to Garmin power ground.

Note what Bob said above. Make sure the correct output/com port is selected, since Garmin has 2 ea. Also, you may have to select the correct NMEA sentences for the ICOM. The ICOM manual should tell you what sentences it reads and the Garmin manual should tell you how to select the output sentences.

Good luck and let us know how it came out. You'll be proud when it's over.

Boris
 
DONE! And they appear to be "communicating". "GPS" shows on the VHF screen and when I tested it per the Icom instructions, it showed lat/long on the radio.

Funny thing Boris is I found the same website you posted by Googling different variations of what I needed to do. Thank you all for your help! This place rocks!!

I basically completed all the electrical/wiring issues I needed to do, but had put off; complete radar install, wired the Icom to the Garmin (DSC), moved the compass away from the GPS per Garmins' instructions and hooked it to power for the light, cleaned up all the new, non-factory wiring by enclosing it all in white mesh sleeving, installed a remote speaker for the Icom...I even marked all the new wires w/ labels. 8)

Now to just learn how to use/read the radar. :lol:
 
You'll find the radar fairly straight forward to use. Just run it a few days when it's clear outside and you'll soon be able to correlate what you see on the screen with what you see with your own eyes. You'll probably be surprised at how some boats have very small radar signatures and don't show up until you're very close while others look "big" on the screen from quite a ways away.
 
That is the plan, Roger. Going out crabbing next weekend and hopefully the weather will be clear enough and I can play w/ the new toy. My lower back hurts from all the contorting that was necessary, but I'm glad it's all done.
 
Also on the radar do not leave it on "auto tune" Experiment with the gain, sea clutter and rain settings. Try the different ranges. Also be sure it is aligned with the heading of the boat.

Good job on the wiring--it will pay off down the line!
 
localboy,

Doesn't it feel great when you've worked your way through how the wires connect, you wire the things up AND THEN EVERYTHING WORKS. Congratulations.

Let me echo Roger's advice on the radar. You have to use it when you can see outside, otherwise it's useless when you really need it. There's a JRC on Journey On, and I have to re-learn that thing every year. One year I didn't bother, and I damn near hit a fishing boat coming out of Ventura in the fog. Judy and I had quite a discussion. Use it or lose it took on a new meaning!!!

Boris
 
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