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Connecting your GPS to you DSC VHF radio

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Voyager
Master Marine Consultant

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USA
5236 Posts

Initially Posted - 08/27/2017 : 10:00:14

Many people have VHF radios with a DSC (digital selective calling) Panic Button and I'd bet most people understand how DSC works.
What it provides is an automated way to alert the USCG or other local first responders to a life threatening situation on or near your boat, equivalent to a MAYDAY or PAN-PAN call.

The system works by digitally broadcasting your unique identifier called an MMSI and other information associated with your radio on your boat. You can obtain an MMSI by going to the BOATUS website and registering at https://www.boatus.com/mmsi/
Another piece of information is the local time of the incident and your GPS coordinates. These two pieces of information are key to first responders.

Time and GPS data are supplied by your onboard GPS wired using the NMEA basic interface. A little more that 2 cans and a string, the interface consists of a traditional 3 wire serial interface where info from the GPS is received as "sentences" of data including date:time:latitude:longitude and other info. A newer version of NMEA is available that is IP based. Newer chartplotters and radios will use the IP interface.

Once you hit the panic button the radio transmits the data and switches to Ch16 with a loud tone. This would alert everyone on board.

The benefit of DSC is that anybody on board can use it in case of an emergency. You can still, however, get on Ch16 and say "MAYDAY-MAYDAY-MAYDAY Vessel "Quid Pro Quo" has been struck and is taking on water. We're located 3 mm south of Pontious Point in 25 feet of water. MAYDAY".

But if grandpa goes overboard with the young kids onboard many of them will not have the know-how to call for help on the radio. They can however press the panic button and await instructions from the USCG. It's not idiot proof either, since nature continually produces more effective idiots. But it is worth knowing about.

I found out that my DSC works. One day I was running through all the settings on my radio - there are plenty. A little while later my phone rang, it was my daughter. She told me the coasties called the house. They asked for me. They gave her their local phone number and asked me to call them. I did.

The Coast Guard safety officer told me that I did not issue a false alarm, instead I inadvertently sent a test message of some sort. It was the first time they'd received this message so they wanted to check it out.

There are several other uses for DSC, like identifying nearby commercial shipping and their locations (good for fog) or pinging one other specific boat whose MMSI you know.

Has anyone set up or used this feature? It would be interesting to get together to write a short blurb on it.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Stinkpotter
Master Marine Consultant

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Djibouti
9016 Posts

Response Posted - 08/27/2017 : 11:16:45

I have never succeeded in making the connection from my GPS to my DSC radio work. The documentation for the two units don't seem to coincide, so I've tried several combinations... I could still push the panic button, the identities for me and my boat will appear to the USCG via the MMSI, and the radio will switch to 16 to communicate... I'll have to know where I am (and can get lat/lon off the GPS or phone quickly).

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 08/27/2017 11:19:41

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 08/27/2017 : 17:20:38

I saw a good article on connecting two units that predate standardization of wire color codes, but I'm not sure where. It might have been BOAT/US or Practical Sailor. I'll have to do some research when I get a chance.

I did hang a laminated card with instruction next to the radio for newbies.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

Edited by - Dave5041 on 08/27/2017 17:21:46

Stinkpotter
Master Marine Consultant

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Djibouti
9016 Posts

Response Posted - 08/27/2017 : 19:13:07

Likewise, I have a 2-sided, one page sheet in a zip-lock letter-sized case with instructions for calling on the radio on one side, and running the boat on the other. Everything is a simple as I could think of, but hopefully effective if ever needed. (Laminating is even better, but I figured I'd probably think of an improvement...)

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

sethp001
Mainsheet C-25 Tech Editor

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814 Posts

Response Posted - 08/28/2017 : 17:14:55

Folks who are not members of BoatUS can get an MMSI for free from the US Power Squadron here: http://www.usps.org/php/mmsi_new/index.php

In one of my few forward-looking decisions, I bought a Standard Horizon Explorer GX-1700 with built-in GPS. I don't think DSC is important on our relatively small inland lake, but I finally acquired a trailer and now can go to the coast!

The GX-1700 is a good radio with a small form factor. It also picks up a GPS signal without any problem despite being mounted below deck. Its also waterproof, so you could mount one in the cockpit with its flush mounting kit, sold separately. There is also a face cover sold separately. http://www.standardhorizon.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=83&encProdID=8E6B84CBCC75E5A9C52CA71AA33BA6F5&DivisionID=3&isArchived=0

Standard Horizon's Explorer GX-1600 is the same model, but requires an external GPS. Standard Horizon makes a compatible external GPS antenna that can be mounted on deck.

Also a word of caution about the GX-1600: it will continuously blare error messages about not having GPS coordinates if you enter an MMSI without connecting a GPS feed. My buddy ran into this problem and had to send his radio back to Standard Horizon to have his MMSI removed, cost $15 plus shipping.

Seth
"Outlier" 1987 Catalina 25 SR/SK/Traditional Interior #5541
"Zoo" 1977 Morgan Out Island 30
"Nomad" 1980 Prindle 16
"Lost" 1988 Catalina Capri 14.2 (sold - yay!)
"Marine Tex 1" Unknown Origin POS 8' Fiberglass Dinghy
https://whichsailboat.com/2014/07/27/catalina-25-review/

Edited by - sethp001 on 08/28/2017 17:22:14

Voyager
Master Marine Consultant

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USA
5236 Posts

Response Posted - 08/28/2017 : 20:04:32

Just to comment on Dave Stinkpotter's comment, setting up serial communications can be one of the most frustrating exercises known to humankind. There are several gotchas:
1. Electrical compatibility. With three wires your chances are 1/3. With two three wire interfaces here's what I do. Find negative ground (GND) on both sides - connect them. Then each side has a transmitter (TXD) and a receiver (RXD). You can use a voltmeter to find the TXD versus GND because it usually has a +12VDC or -12VDC on it. RXD should have no discernible voltage relative to GND. So connect the TXD or the HF to the RXD of the GPS and vice versa.
2. Set baud rate or data rate. The radio expects 4800 bits per second (bps) or baud with no parity. Set your GPS to 4800 baud.

Two additional issues could create problems.
� This assumes your devices use NMEA0813 serial protocol. If you have NMEA 2000 on one then you're out of luck.
� If you can't set baud rates you're also dead
It's great when it works though.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 08/28/2017 20:09:49

TakeFive
Master Marine Consultant

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2269 Posts

Response Posted - 08/29/2017 : 16:22:58

My GX2150 radio is interfaced with a Garmin 18xLVC GPS puck to provide proper DSC/panic button operation. Some of their newer radios have GPS built in, which is great as long as electrical noise from your 12v panel does not interfere with GPS (mine did, requiring me to move the GPS puck several feet away from the radio.

I was interested in having my laptops able to share the GPS and AIS signals, so I also attached Bluetooth transmitters to broadcase both. Now any onboard computer can pick up GPS and AIS and display them using chartplotter software.

I wrote some of this up in Mainsheet about 5 years ago.

Rick S., Swarthmore, PA
PO of Take Five, 1998 Catalina 250WK #348 (relocated to Baltimore's Inner Harbor)
New owner of 2001 Catalina 34MkII #1535 Breakin' Away (at Rock Hall Landing Marina)

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 08/29/2017 : 17:07:37

I've been using the same old bluetooth gps puck forever. $39 more than a decade ago.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

TakeFive
Master Marine Consultant

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2269 Posts

Response Posted - 08/29/2017 : 17:58:42

quote:
Originally posted by Dave5041

I've been using the same old bluetooth gps puck forever. $39 more than a decade ago.

How do you get it into your VHF radio for DSC?

Rick S., Swarthmore, PA
PO of Take Five, 1998 Catalina 250WK #348 (relocated to Baltimore's Inner Harbor)
New owner of 2001 Catalina 34MkII #1535 Breakin' Away (at Rock Hall Landing Marina)

HerdOfTurtles
1st Mate

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USA
68 Posts

Response Posted - 08/31/2017 : 13:17:11

I haven't found an appropriately priced GPS solution so no, I have not hooked up the DSC to my VHF and just deal with the annoying alarm that goes off when you power it on.

1978 Standard Rig
Fin Keel
L-Dinette

Voyager
Master Marine Consultant

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5236 Posts

Response Posted - 09/02/2017 : 10:22:16

It's important to distinguish between three-wire serial ports (transmitted data, received data and ground) and USB ports (shared bus for data packets, plus +5VDC and ground).
Older handheld GPSs, including most older pucks, use the former three wire interface.
Newer GPSs and pucks provide a USB interface. The Standard Horizon radio I have is a GX1000S that uses the three-wire NMEA 0183 interface. With newer USB pucks, you'd need an adapter or a computer to convert from USB to three wire serial.
The protocol is important too. Here's an article that discusses the protocol and GPS sentences. My guess is that the radio only needs position, speed and time from the GPS. Many other pieces of data are available.
The setup need not be overly complicated, just basic data. The biggest problems most people encounter are:
1. Figuring out the wiring (txd, rxd, gnd)
2. Setting the bit rate at 4800 baud
3. Determining the sentences for latitude, longitude and time.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 09/02/2017 10:34:15

TakeFive
Master Marine Consultant

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2269 Posts

Response Posted - 09/02/2017 : 10:45:26

Garmin 18x LVC meets all the required specs for interfacing with VHF on NMEA0183 protocol. $60-70 is not too much to spend for a critical safety feature that could save your life. Optionally, splice in a USB-serial adapter and you can plug it into your laptop and run navigation software on your laptop.

Rick S., Swarthmore, PA
PO of Take Five, 1998 Catalina 250WK #348 (relocated to Baltimore's Inner Harbor)
New owner of 2001 Catalina 34MkII #1535 Breakin' Away (at Rock Hall Landing Marina)

Stinkpotter
Master Marine Consultant

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Djibouti
9016 Posts

Response Posted - 09/02/2017 : 13:29:53

quote:
Originally posted by HerdOfTurtles

I haven't found an appropriately priced GPS solution so no, I have not hooked up the DSC to my VHF and just deal with the annoying alarm that goes off when you power it on.

If your saying you haven't put in an MMSI into your radio, there's no requirement for a GPS connection in order to have the USCG know about your boat, you, your contacts, etc., and be able to bring it up when you press the red button. You'll have to tell them where you are when they hail you, which will inform other boats in the area.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Voyager
Master Marine Consultant

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USA
5236 Posts

Response Posted - 09/02/2017 : 16:56:21

Getting an MMSI ID is free. Takes about 10 minutes to register.

I originally registered on BoatUS' website for free back in the day, but now I see they get you for $25.00. If instead you go to SeaTow, they will register you for free.

Maybe I missed it, but I saw lots of info on the USPS.org website, but no way to register for and MMSI. Here's the SeaTow site: http://mmsiregister.seatow.com/Account/Register If you have a DSC radio, even if you don't have your GPS connected, you should have an MMSI for your boat and it should be programmed into your VHF.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

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