A comment on this Icom M506 article pointed out that most people only have one VHF on their boat, and hence the issue I discovered when using two of them has limited impact. He's right, but hold on a minute before you run out and buy an M506 with NMEA2000. I did just that for a small runabout that we recently got, and was in for another unpleasant surprise.
We recently got a Grady White open boat and I picked and installed electronics for it. It's a very simple system - about as simple as you can get - a Furuno TZTouch2 multi function display plus an M506 VHF. As I've said before, I really like the M506 as a VHF, but find the optional NMEA 2000 interface to be pretty seriously broken. But in this super simple, bare bones config of a single MFD and a single VHF, I figured my chances were pretty good that it would all work. Wrong again.
First off, the M506 continues to appear to the TZ2 as a valid data source for just about every imaginable type of data. Take a look at the screen shot below. Really? The M506 is a good source for rudder position, rate of turn, atmospheric pressure, outside temperature, etc? Come on.
|M506 says it's a data source for pretty much everything|
But it gets better. The TZTouch2, like many MFDs, has a built-in GPS. This is very convenient for an open boat where you can get an acceptable signal. The TZ2 and M506 both have N2K, so it's just a matter of connecting them together. The TZ2 provides GPS to the VHF, and the VHF provides DSC alerts back. But when I hooked everything up and powered it on, the M506 was complaining that there was no GPS data. How on earth can something so simple from two very reputable companies not work?
Here's what I found.
The TZ2, once you enable a couple of things, puts out a couple of different GPS data messages (PGNs). Both of them include the basic GPS position info, and one includes additional information that reports the general status of the GPS receiver. The TZTouch2 doesn't fill in that status info, but the M506 expects it, and rejects the message when the info is not there. Or at least that's how it appears. What I know for sure is that when I hooked up an external GPS, the M506 started working fine. And when I compared the messages being sent and their contents, the status info was the only difference.
I sent traces to Furuno since this time is looked like the TZ2 was the culprit. They replied that this was a known issue and that they were working on it.
To add to the confusion, there was an issue a while back between the TZTouch (not the TZ2) and the M506 where AIS data was not passing successfully between the two. I never experienced it myself, but it was widely reported. AIS data received by the M506 was not displaying on the TZTouch. This problem was fixed a while ago by some combination of software updates on the TZTouch and the M506. I'm not sure whether both devices need to be updated to fix the AIS problem, or if updating either of the two will solve it. Regardless, the issue I encountered is completely different, has nothing to do with AIS (my VHF doesn't even have AIS), and I'm running the latest software in both the M506 and the TZTouch2.
Below is a screen shots showing operation with just the TZ2 providing GPS data, and a closeup of the message contents. Then the same thing again with an external GPS. I've circled the missing data in the message from the TZ2 that appears to be the problem.
|Running with TZTouch2 internal GPS (this doesn't work)|
|Missing data in GPS message from TZTouch2 (this doesn't work)|
|Running with external GPS (this works)|
|Notice the data is included in this message (this works)|