Standard-Horizon GX2200 to Garmin 546S AIS noise problem

Nov 22, 2011
1,192
Ericson 26-2 San Pedro, CA
I recently purchased a Standard-Horizon GX2200 VHF radio that has built-in AIS receive capability. I decided to wire this up to my Garmin 546S chartplotter in order to display the AIS targets on the charplotter screen. I did so based on instructions I found on this site. Unfortunately, there is an error in the wiring shown on this site, but it is one that is subtle and did not appear obvious at first blush.

Based on these instructions, I wired the gray lead on the GX2200 (DSC Output +) to NMEA (in) on the Garmin (violet, because I was using Port 2). I also wired the brown lead on the GX2200 (DSC Output -) to power ground. Note that on the Garmin, power ground serves double duty as NMEA ground. Everything worked just fine from the standpoint of showing AIS targets on the chartplotter. So I figured all was right with the world.

Then I began to notice a scratchy noise I had not observed prior to this. The noise would go away when I removed the brown lead from ground. The presence of the gray lead on the GX2200 had no effect one way or the other.

I thought that perhaps there was some piece of equipment on board generating the noise that was somehow being picked up, so I disconnected the battery from the panel and also removed the shorepower cord. I then wired the radio directly to the battery with no other equipment on the boat running. The noise was still there with the DSC Output - wire grounded. I hooked in my old non-AIS GX1700 just for comparison and there was no noise on it. Clearly this noise was being generated within the radio itself.

Here is what I discovered (and subsequently confirmed through Yaesu tech support. Note that SH is owned by Yaesu.)

In going through the GX2200 manual I found this note on p. 19. "Note: Some GPS chart plotters have a single wire for NMEA signal ground. In such a case connect the NMEA input (-) to the GPS chart plotter's single NMEA signal ground wire, and leave the NMEA output (-) open. In case the assignment of power supply and ground of a GPS chart plotter to be used is different from that of the radio, connect the signal ground wire of the GPS chart plotter to the ground terminal (GND) on the rear panel of the radio."

To me, the wording of this note was a bit confusing. But what this means in practical terms is the following:

  • I wired DSC Output + (gray wire) on the GX2200 to the NMEA in on the Garmin 546S (violet, for Port 2 NMEA in). That is the same as before.
  • I wired the GREEN wire on the GX2200, which is NMEA GPS Input (-), to power ground.
Note that the last sentence of the note is not applicable to my case because my Garmin is connected through the same panel as the GX2200.

Yaesu tech support concurred with my interpretation of that paragraph. In fact, at that point they had the radio in their possession for troubleshooting when I came across the note in the manual and e-mailed it to the tech. They were thus able to bench test it using this info and did see the noise with the brown lead to ground but not when the green lead was grounded.

Now I no longer have the noise but still see my AIS targets, as before.

Hopefully this will be of help to someone.

P.S. The wiring I discuss in this post definitely applies to the GPS546 and most if not all Garmins of that vintage. For all I know it may apply to current models as well, but you would need to confirm that for yourself.
 
Last edited:
Nov 22, 2011
1,192
Ericson 26-2 San Pedro, CA
Thank you for the information
You are very welcome. Troubleshooting these kinds of issues can be maddening, especially when things "sort of" work. Hopefully my sharing this info might prevent someone from sending in a perfectly good radio for an unnecessary "repair."
 
Nov 21, 2012
587
Yamaha 33 Port Ludlow, WA
Thanks for providing this, it's what makes this site so useful. I have a Garmin 741xs and the SH 2200. I wired it up as described in the article referenced above and have not had any issues.