Garmin/Icom Interface

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richardbrennan

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I have recently upgraded my old Garmin 2010 and fitted a Garmin 5012 which tells me it will receive DSC information by NMEA 0183. I have rather a mix of electronics on Board, the radar, sailing instruments and autopilot are Raymarine, the radio is an Icom M505 and the plotter, as I already said, is a Garmin 5012. I have a Seatalk/NMEA 1083 interface box and everything talks to everything else except I do not appear to be getting the NMEA signal from the Icom into the plotter.

The NMEA out wire from the radio is a white lead with a single wire giving the NMEA Out + and sheaving giving the NMEA out -. I have connected this to receiving port 2 on the 5012 which has a brown wire for RX+ and a brown and white wire for RX-. I have the NMEA Output selector in the Icom selected to "All Stations" and the NMEA RX port on the Garmin I have tried in both NMEA Standard and NMEA High Speed as the Icon transmits on NMEA 0183 ver3.01 which I believe is high speed.

I had various DSC calls and position requests made to me, but although they are coming through on the radio, there is nothing showing on the plotter screen although the awful Garmin manual does not make it very clear what I am expecting to see. Also, if I go into the diagnostics on the Garmin it shows a "not being received" message next to DSC.

I have tried wiring to different ports on the Garmin and wiring the - side to earth but all to no avail, the plotter is definitely talking to the Icom as the position of the boat is displayed on the DSC screen but this does not appear to be happening the other way round.

I really do not know where to go from here except long calls to both manufacturers, but it seems to me that there is simply no NMEA output coming from the Icom and I wonder if I can check this with a multimeter, does anybody out there know what I am likely to see. Any other suggestions are welcome and if anybody has the same or a similar setup that is talking both ways I would be grateful to hear from them.
 
I have a similar icom radio and a Garmin 5012. As far as I can remember the only thing you can get to pass between them is a position, and that's from the 5012 to the VHF.

I stand ready to be corrected, but what were you expecting to pass across?

Just to add to that, I am pretty sure that the 5012 will only accept dsc stuff from a Garmin VHF. You could check with their UK tech support though as they are easy to get hold of and very knowledgeable.
 
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Dear SolentBoy

If you look at page 49 of the Garmin Manual there is a table and apart from the plotter sending the GPS position to the radio, it states:

The chartplotter can receive DSC distress and position information from the radio.

The chartplotter can track the positions of vessels sending position reports

I am not quite sure what this looks like but it does illustrate the signal from a distress call over the page. This is for any DSC radio not a Garmin which has a seperate column
 
richardbrennan said:
I had various DSC calls and position requests made to me, but although they are coming through on the radio, there is nothing showing on the plotter screen although the awful Garmin manual does not make it very clear what I am expecting to see. Also, if I go into the diagnostics on the Garmin it shows a "not being received" message next to DSC.
Click to expand...

The way I read page 55 of the manual for your radio this output appears to be restricted to Position acknowledments....

It might be worth a chat to Icom service dept as they are usually helpfull.
 
richardbrennan said:
Dear SolentBoy

If you look at page 49 of the Garmin Manual there is a table and apart from the plotter sending the GPS position to the radio, it states:

The chartplotter can receive DSC distress and position information from the radio.

The chartplotter can track the positions of vessels sending position reports

I am not quite sure what this looks like but it does illustrate the signal from a distress call over the page. This is for any DSC radio not a Garmin which has a seperate column
Click to expand...

You learn something new every day. I shall have a play with that next week on my boat and see if it works. Good luck..
 
SolentBoy said:
You learn something new every day. I shall have a play with that next week on my boat and see if it works. Good luck..
Click to expand...

Beware.....In order to do this it needs the DSC to actually transmit the correct info as recieved from the DSC alert. However the Icom 505 suggests it only transmits position info from position acknowledgments....If this is true it might not not be sending from DSC alerts . MInd you it could just be bad japanese english which is why I suggested the OP speak to Icom.

I would listen to the Nmea output using a high imedance earpiece but not everone has one:)
 
On my previous boat I had a Icom 505 that did talk to a Standard Horizon CP300 plotter. So I do believe the ICOM does put out DSC calls. As I remember only the 505 and the 605 model have this capability.
What might be an issue is that Icom uses the supply negative as NMEA (-) wich can be a problem if the receiver expect a true RS422 signal. You can use a multimeter to see if any data is sent from the radio. Just measure on a 12 volt DC setting and you should see the some voltage hiccups when it receives a DSC call. Mind you the message is quite short, so it will only show for a second or so, best to use a analogue meter. You could also connect the radio output to the serial port of a laptop to analyze the message in more detail. In my setup the ICOM was connected to the plotter via a NMEA multiplexer that may have been a bit more easy on the signal characteristics.
 
Dear Aluijten

I am afraid you have lost me with reference to "a true RS422 signal" if you could explain this in simple terms it would be appreciated.

Also can you tell me what indications you got on the SH CP300 from the Icom?

Many Thanks
 
I have none of the equipment mentioned in this thread so this may be a completely spurious response.

However, it occurs to me that the ICOM may only output NMEA position info when there is a genuine DSC distress call received that includes position info. It could well be that no such DSC distress call has been received while you are checking the kit.

I have no idea how you could test this theory - the Coastguards do not like 'test' DSC red button calls!
 
I'll watch any developments on this with interest, as I have an Icom M505 connected to a Garmin 4008, and I too do not get DSC information on screen. It is difficult to test the system, as Playtime suggests, you can only see if what you have done by way of installation has been effective, when there is a DSC alert.
 
galadriel said:
It is difficult to test the system, as Playtime suggests, you can only see if what you have done by way of installation has been effective, when there is a DSC alert.
Click to expand...

According to the manual, if set on the menu, the M505 outputs NMEA position when receiving position acknowledgement. A test should be possible by asking for just a position report from another boat. An alert isn't necessary.
Mine isn't so connected, so can't test this.
 
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earlybird said:
According to the manual, if set on the menu, the M505 outputs NMEA position when receiving position acknowledgement. A test should be possible by asking for just a position report from another boat. An alert isn't necessary.
Mine isn't so connected, so can't test this.
Click to expand...

I've also now taken a quick look at the M505 manual and agree that, if it works as described in the manual , it should be possible to test NMEA output from the ICOM to the Garmin by requesting a position and receiving a position acknowledgement from another boat. This does, of course, need the other boat to be in VHF range with both it's VHF and GPS turned on (and properly connected!) and you need to know its DSC ID.
 
Richard,

RS422 is the basis behind NMEA 1.0 upto 3.whatever. NMEA-2000 uses CANbus (high-speed).
RS422 is almost the same as RS232. RS232 is what used to be on every PC until USB came around. The difference between RS232 ans RS422 is the voltage used. More specific, RS232 is based on 0 Volt and 12 Volt, RS422 is a current-loop system. For RS422 it's not the voltage that is important, but the current though the wires. Obviously there is a relation between the both. But if you have very long cables, current-loop is more robust as the sender needs to increase the voltage to get above the current threshold (because long cables have higher resistance and V=IxR, Volt is Amps times Ohm). Because quite often you are able to drive a RS232 receiver with a RS422 sender, there is a lot of mix up even by manufacturers.
So to make a long story short :-) , a RS232 connection has a signal ground and a signal line, a RS422 has a signal positive line and a signal negative line. If you would use a voltmeter you would see the voltage of RS422 swinging between -12 volt and +12 volt (between the two lines) and RS232 between 0 and 12 volt.
By the way, many systems only use 5 volt these days. Most equipment is tolerant enough for this.
What could be the case is that your plotter expects -5 volt for a logical 0 and +5 volt for a logical 1 (computers work with zeros and ones). The Icom sends out 0 volt for a logical 0 and +5 volt for a logical 1 (could be +12volt as well, I'm not sure). So your plotter sees the 0 Volt as a undefined state and not a logical 0 => no communication.

So how to solve this? I had this situation myself once and could solve it with some resistors and capacitors but in all honesty I forgot how :-(
What could do as well is is make use of a NMEA buffer or repeater. These tend to have very wide acceptance levels for serial signals (RS422 or RS232).

To your second question:
My ICOM 505 repeats the response to location requests and the origin of DSC distress calls (position) through the NMEA port. So if your friend sends a location datagram to your VHF (via DSC), the ICOM will output the location via the NMEA port.
I had this working with a friend that used a Raymarine VHF for this.

Cheers,

Arno
 
Stork III the port on the Garmin is set for NMEA, there is a choice of standard, hi-speed or Garmin, I have tried both NMEA settings and will now, with the information from Playtime, make sure it is set to standard. I will try and get a test position request call made next time I am down on the boat, I was amazed on Saturday how few people around had DSC radios and the odd one that had one did not know how to make an individual call or had put in any other boats into the directory. Makes me wonder how many of us out there are actually using DSC other than to have the reassurance of the little red button!
 
I have now spoken to both Icom and Garmin Technical Support. It would appear that the Icom will only send a signal when it receives either a distress call or a position request either to or from another vessel. This would explain why the Garmin is showing "DSC not received" when simply wired up but with out these calls being made. I am assured by both manufacturers that connecting NMEA out on the Icom to a receiving port on the Garmin should enable the plotter to show the position of vessels in distress and position of vessels making position reports and that it will plot the latter, this is covered, but not too clearly, in the Garmin Manual on pages 50 & 51. Hopefully when I am next on the boat I will be able to find someone with whom to exchange such calls. I will report back.
 
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