Instructables

Connecting a handheld GPS to a Marine VHF radio

Explains how a connected a low cost handheld GPS to a low cost (on sale) VHF marine radio. This supports DSC (digital selective calling) and automated distress calls.

(I'll upload some photos of this tonight)
 
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Step 1: The parts I started with

The VHF radio - I picked this up new, at a really good price due to a sale. In the process I also learned that it can be connected to a GPS and learned how the automated distress signal works. I also learned that with DSC it can send position info to other boats.
(note: at the time of purchase, I didn't know it could work with my handheld GPS)
The ETrex GPS - really cheap haldheld unit that has served well over the last couple of years.
DB9 Serial Connector - from an old computer. You should be able to find this at your local electronics shack.

Step 2: Figure out if it can work

The manual for the radio states that accessories need to implement the NMEA 0183 standard (I later learned what this is).
A google search for NMEA and ETrex shows a site listing GPS units that support the standard. Mine is listed, woohoo.
I later discovered that in the setup menu in the GPS, its a communication option (I should have checked the device first).

Step 3: Wire things up

I hooked up the serial interface cable to the GPS, next, I googled for the pin diagram.
It shows serial communication from pin 2 or 3 and the ground on pin 5.
I fire up the radio and the GPS.
I just stick the bare ground in the number 5 hole in the serial connector, and the other wire in the pin 2, nothing happens. Move it to pin three, a few seconds later, life. Woohoo.
usmmjenny7 months ago
Get yourself an EPIRB (emergency position indicating radio beacon).
I would like a Hand-Held GPS device that allows me to 1) upload the coordinates selected as I walk a property into my PC and a map from MS S&T down into it. Just thoughtto ask if you had any insights into this and could help.
PaulE (author)  charlessenf-gm6 years ago
My particular (I'd assume most) when in NMEA mode continuously send position data over the serial port. So, if your PC is connected, just have it log it somewhere.
Marv20976 years ago
I think VE6-OMG just hit the point, Amatuer radio is what it says it is, for Amatuer use. When dealing with sending of distress signals you should be using equipment that is designed for that purpose and nothing else.

The whole point of using GPS with a Marine VHF and not a HAM or other radio is thats what the Coastguard, RNLI and more importantly every other ship at sea will be listening on ch16. It is also important to note that when using DSC to send a mayday a normal 'Mayday Mayday Maday' should also be broadcast on ch16.

If your VHF and GPS are both submerged both may work but the GPS wont get a good position and the VHF wont be able to transmitt. I think the point of the waterproof kit is that if you drop it in the water or it gets completely soaked it still works afterwords (some of these devices now even float). Can't say i know of too many HAM radios that float very well ;)

As for claims of water resistance, I use a handheld VHF as a backup and this has seen its fair share of dunkings and works perfectly. The GPS is a garmin etrek and is completely sealed. As long as you are not diving with these things I have no doubts they work fine.
VE6-OMG7 years ago
I am sorry to burst your bubble. But now in amatuer radio it is possible to send position, heading, and digital paging through GPS with Ham radios
PaulE (author)  VE6-OMG7 years ago
You are absolutely correct but, some of the reasons that a HAM radio won't meet my specific application are: - that radio can work while submerged under water, a must for emergencys on a 16' sailboat - a single button to automatically hail the Coast Guard with position info (for instance, I get knocked overboard and my non-english speaking wife has to get help). - standard marine VHF freq's and DSC standard compliance - price. That VHF rig cost me $120 + $80 for the GPS. That's not even realistic entry money for a ham rig - the ability to monitor 3 channels at once (a scanner could do this but, add some more money)
WA2ZDY PaulE7 years ago
Paul, you're correct, a ham radio will not serve your needs. But please, don't believe your radio is going to work for you whilst submerged. Height above the water is what gives you distance. A handheld radio at water level is going to get out a couple miles at most. Submerged, if your radio and/or GPS still works (don't tell me about the claims of water resistance,) the transmit range of a submerged VHF antenna can be measured in dozens of feet. Please just don't expect more than your radio can possibly offer.
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