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Garmin 942xs to Icom 502 NMEA help

Old 11-13-2020, 07:48 AM
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jlr
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Default Garmin 942xs to Icom 502 NMEA help

I am trying to output position speed and time from my Garmin 942XS chartplotter to my Icom M506 VHF. Contrary to the Icom manual, there is no RCA connection on the back of the Icom. Icom says to use the green wire (neg) and the yellow wire (pos). Garmin appears to use the gray wire(neg) and the blue wire(pos). However, when I connect it this way, using NMEA 0183, I receive no data or at least cannot display the data on the Icom. The baud rate on the Garmin is set to standard, not high speed. Any help with this NMEA 0183 wiring would be greatly appreciated.

Last edited by jlr; 11-13-2020 at 09:05 AM.
Old 11-13-2020, 08:07 AM
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According to the Garmin manual, on the 942, NMEA 0183 transmit is TXA+ (blue wire) and TXB- (gray wire); the Icom has an RCA connector which requires you to use an RCA male to wire adapter and connect the center wire (+) to the Garmin blue wire and the outer wire to the Garmin gray wire.
Old 11-13-2020, 08:33 AM
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Unfortunately, the Icom manual online is inaccurate according to Icom. There is no RCA jack and Icom said to use the green and yellow wires, with green being negative and yellow being positive. However, after I did so, connecting the green Icom to the gray Garmin and the yellow Icom to the blue Garmin, it did not work.
Old 11-13-2020, 09:04 AM
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You may need to configure the NMEA 0183 output settings of the 942. The instructions for this can be found on page 60 and 61 of the manual.
Old 11-13-2020, 09:04 AM
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Sorry. My error. Same questions but I have an Icom 506 not 502. Any help much appreciated.
Old 11-13-2020, 09:21 AM
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Double check the that 942 is set correctly on its output ports. I believe it defaults to Garmin and it needs to be set at NMEA Std. To check this go into the menu >Settings >Communications >NMEA 0183 Setup and then select NMEA Std. and see if that solves the problem.
Old 11-13-2020, 09:35 AM
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Wiring appears to be okay. Since you checked the baud rate, I assume you also checked for the correct output sentences.
Have you run 0183 diagnostics? Settings > Communications > NMEA 0183 Setup>Diagnostic
Old 11-15-2020, 05:43 AM
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Originally Posted by jlr View Post
Unfortunately, the Icom manual online is inaccurate according to Icom. There is no RCA jack and Icom said to use the green and yellow wires, with green being negative and yellow being positive. However, after I did so, connecting the green Icom to the gray Garmin and the yellow Icom to the blue Garmin, it did not work.
Now that we know it is a current M506 instead of a 20 year old M502, the wiring is simple: Garmin NMEA 0183 transmit is TXA+ (blue wire) and TXB- (gray wire); Icom NMEA 0183 Receive is RX+ (yellow wire) and RX- (green wire), so blue to yellow and gray to green. That appears to be the same as what Icom told you on the phone concerning the yellow and green wires (see p.101 of the Icom M506 manual).
If you are going to use DSC on the Icom M506, you also need to connect the NMEA 0183 output (white wire is TX+ and brown wire is TX-) from the Icom M506 to the Garmin - or you could just use the NMEA 2000 system and make the job easier.
From there you need to configure the Icom to use NMEA 0183 in the configurations menu.
Old 11-17-2020, 05:10 AM
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All working now. I needed to turn on some extra NMEA 0183 sentences. Thanks for the help.
Old 11-22-2020, 01:50 AM
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While I am now getting the information from my Garmin to my VHF, I noticed yesterday that the course information is showing on the VHF as true rather than magnetic. I cannot find a setting on the VHF to change that nor can I find a setting on the Garmin to change the NMEA output sentence(s) to magnetic rather than true. Any help still appreciated. Thanks.
Old 11-22-2020, 06:09 AM
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I am unaware of any way to capture magnetic headings over NMEA 0183 outputted from a chartplotter - most GPS units (chartplotters, autopilots - not sure about VHF) will receive sentence "HDM" which is heading magnetic, but as far as I have seen only heading sensors output that sentence. Chartplotters output "VHW", which is heading actual or true.
Old 11-22-2020, 08:18 AM
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Thank you. Surprised that the Garmin will not output a magnetic heading over 0183.

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