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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Connecting a GPS to your DSC capable VHF?

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Initially Posted - 05/24/2008 : 13:06:10

OK, I've been trying to make this work for a couple of hours now, and can't seem to figure it out. Both the Garmin instructions as well as Uniden's instructions seem deliberately vague. It would seem that you should hook up one data out cable to a data in cable on the receiving device (VHF), and the same for the data in to out, but apparently it's not that simple.

Do I need to connect two or four wires to make the GPS talk to the VHF? Has anyone done this who can provide instructions or assistance? It's driving me crazy.

Next I need to figure out the same thing for my auto-pilot, but I'm more concerned about the VHF for safety.

TIA for any assistance you can render.

David
C-250 Mainsheet Editor

Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 05/24/2008 : 13:48:44

They will probably use the 'NEMA 0183' standard to connect.
A minimal connection is 3 wires if you use a common ground, or there may be 4 wires if you run
seperate negative leads between the 2 units.

Positive In (In +) connects to Positive Out (Out +)
Negative In (In –) connects to Negative Out (Out – or Gnd)
Positive Out (Out+) connects to Positive In (In +)
Negative Out (Out -) connects to Negative In (In – or Gnd)

The rest of the problem is finding the pin-outs from the mfg's to connect the in's and out's together.

Edited by - on

Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 05/24/2008 : 22:26:16

David, if you still have trouble after Bruce's advice let us know. I hooked up a Garmin chartplotter and an iCom VHF last year. I recall the directions were vague. I may have made notes in the manuals that would be helpful and can check the wires where they come together. Once connected, the DCS capability works great.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 05/25/2008 : 11:41:21

Randy,
If you have any notes, that'd be great. I figured out one stupid thing I'd done, I didn't have the GPS set to connect NMEA-NMEA, so I've fixed that but still no joy yet. However, I'd convinced myself that I only needed one pair of NMEA input/output connected and it would work. I had cut short all the wires that I <i>thought </i>I wouldn't need and attached the ones I thought I did to a 4-wire connector (same as the mast deck connector on my boat). Apparently that's not going to work, so I'm going to strip all the wires and hook up all four to the radio. I figure at worst I can only be wrong 15 times (only 16 possibilities). Once I get that figured out, then I have to figure out the hookup to the autopilot, which only has two NMEA connections. The instructions for my AP are even more vague, they never refer to a GPS unit, instead they refer to a "navigator".

I wonder why they make this so vague?

Have you applied for your MMSI? I have not yet.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/25/2008 : 12:19:51

David: I believe if you only want your GPS to give your position to the VHF to transmit with a DSC distress signal, you only need to connect the Out pair (+/-) from the GPS to the In pair on the radio. The other connection allows the radio to tell your GPS the position of another DSC distress call to place a symbol on your screen. I would try hooking up the former connection first, make sure your GPS is configured to transmit a NMEA "sentence" (generally a setting in the GPS software), and see if you get a lat-lon displaying on the VHF. The latter connection will be hard to verify unless somebody is issuing a Mayday via their DSC radion nearby.

Edited by - Dave Bristle on 05/25/2008 12:22:44

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 05/25/2008 : 14:18:01

Dave,
That was the trick. I'd wrapped my head around the connections like they were connecting a load, so you'd want an in with an out (from the GPS) to go to an in/out pair on the VHF. Once I looked at it from the proper point of view (out/out to in/in), the first connection I made worked. Phew! I was beginning to doubt that I'd ever been an electrician in a former life! Now I'm off to WM to find another style of connector and some small gauge cabling.

Thanks for the help guys, and I'll post my cabling connection pairs later on so if someone else comes up against this they'll have a place to start from.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 05/25/2008 : 20:11:54

So, now that I have the GPS -> out part working, is it possible to test whether GPS <- in is working (bearing in mind that I'm 20+ miles from the water). How do I simulate a DSC call? Anyone know if this is possible? Before I make up my cables, I want to know that I've got them hooked up the right way.

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Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 05/25/2008 : 23:42:21

You should see your coordinates in the VHF screen when both the GPS and VHF are on. That's how my iCom M304 works.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/26/2008 : 00:22:27

David: As I said, I know of no "test" for the "Out" connection from the VHF--it requires a Mayday DSC transmission from another boat, and "radio checks" are not legal for this purpose. Just hook it up as documented--you will <i>probably</i> get the data from a vessel in distress.

Edited by - Dave Bristle on 05/26/2008 00:24:33

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 05/26/2008 : 10:55:46

I've done a bit of research on this, it looks like you can test this using Windows Hyperterminal...somehow. My current plan is to connect the outs/ins to a terminal block. I already know I've got the outs figured out, and I can only be wrong once with the ins, so at worst I have to swap connectors on the terminal block if it doesn't work when I get my neighbor in the marina next to mine to shoot me a DSC call.

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