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Author Topic:   VHF Marine Band Radios with Integral GNSS Receiver
Hoosier posted 10-26-2013 10:11 PM ET (US)   Profile for Hoosier   Send Email to Hoosier  
Why don't all fixed mount DSC radios have a built-in GPS receiver? My DSC handheld does but my brand new Lowrance Link 8 DSC radio doesn't. Hell, you can get a digital camera with internal GPS so you know where your pictures were taken.

[Initially posted as a sidebar to another discussion in which the low rate of use of GPS-position aided DSC calls was being lamented, this article has been moved to its own thread.--jimh]

jimh posted 10-26-2013 10:43 PM ET (US)     Profile for jimh  Send Email to jimh     
There is no guarantee that a VHF Marine Band fixed-mount radio will be installed in a manner that permits an integral GNSS receiver to have a good view of the sky. For example, my VHF Marine Band fixed mount-radio is installed on the lower shelf below my helm station, and its view of the sky is quite restricted.

The notion that a communication device ought to have its own dedicated GNSS receiver is also used in the case of a vessel's AIS transmitter. I was initially surprised to find that a Class-B AIS transmitter would include its own GNSS receiver. I was thinking that the AIS transmitter would just connect to the main GNSS receiver on the vessel and use that source for sending its position. But it appears to be a requirement that the AIS transmitter have its own, dedicated GNSS receiver. In giving some thought to that requirement, I can see that it makes some sense. Having a dedicated GNSS receiver for the AIS transmitter makes the system independent of the rest of the vessel electronics.

I do agree with your observation that many modern electronic devices now contain their own GNSS receiver, and the incremental cost of these GNSS receivers does not seem to be very much. It is also ironic that many of these new devices have better GNSS receivers than you find on most marine chart plotters. The new gadget devices tend to have GNSS receivers, while many marine devices are stuck with GPS-only devices.

Perhaps the best approach might be for the FCC and USA Coast Guard to promote the manufacturers to provide VHF Marine Band DSC-rated fixed-mount radios with external GNSS receivers that could be easily attached to the radio with a simple plug or connector. This would allow the antenna for the receiver to be located in a good position.

Hoosier posted 10-29-2013 09:18 AM ET (US)     Profile for Hoosier  Send Email to Hoosier     
Not to beat this to death but my Link 8 has NMEA 2000 capability so it can get location information from either chartplotter or the rooftop antenna, all of which are on the network. It actually has a feature to automatically select the best signal. The general problem is that there aren't many N2K capable radios and older ones in the installed base may have NMEA 0183, at best. NMEA 0183 is not easy to hook up, and it's point to point, not networkable.

As for needing a clear view of the sky, that depends on what's obsuring the sky. I've found that my Sirius Weather Radar receiver works just fine from inside the console of my Outrage. The signals go right through the fiberglass, I expect GPS signals would too. Also there's the multipath factor, my handheld GPS works fine inside of my car where it doesn't have "a clear view of the sky" in a dashboard pocket between the seats.

jimh posted 10-29-2013 09:25 AM ET (US)     Profile for jimh  Send Email to jimh     
Radios with NMEA-2000 were the topic of a prior discussion. See

The number of boats with NMEA-2000 networks is probably much smaller than the number of boats with VHF Marine Band radios.

These days the gizmo we still call "a radio" is really more of a computer with a radio as part of a sub-system. That is what a modern VHF Marine Band radio actually is. The computer part:

--digital selective calling features, MMSI, messaging, polling, monitoring, etec.,

--serial data communication to other devices, either NMEA-0183 or NMEA-2000

--front panel information display and user interface for operating radio, and

(oh, yes)

--a radio receiver and transmitter.

With all that other stuff already in "the radio", we might as well throw-in a GNSS receiver, too. And, then, while we are at it, let's have an AIS receiver, as well.

K Albus posted 10-29-2013 11:51 AM ET (US)     Profile for K Albus  Send Email to K Albus     
My VHF radio also has a rudimentary chart plotter display. Can we please add a bigger screen with better, more colorful graphics?
jimh posted 10-29-2013 01:44 PM ET (US)     Profile for jimh  Send Email to jimh     
Standard-Horizon tried that with some chart plotter and radio combination devices.
6992WHALER posted 10-29-2013 10:24 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
Sounds like you guys want one unit to do everything. I am afraid it might be a "Swiss Army Knife" it can do everything but it does not do any one thing very well.

I have a VHF radio with a built in GPS receiver as a back up.

But, my Primary Radio is communicating with my Primary GPS/Chart Plotter. I am not sure I want to put all my eggs in one basket. If my radio fails the Chart Plotter still works and visa versa.

jimh posted 10-29-2013 11:16 PM ET (US)     Profile for jimh  Send Email to jimh     
I agree--keep the radio separate from the chart plotter.

But today the VHF Marine Band radio is much more sophisticated and much more interconnected to other sophisticated devices on the boat than my old crystal-controlled four-channel Motorola boat radio of the 1970's.

Hoosier posted 10-30-2013 07:31 AM ET (US)     Profile for Hoosier  Send Email to Hoosier     
"I agree--keep the radio separate from the chart plotter."

I disagree, this is the whole point of this thread. Right now the radio is NOT separate from the chartplotter, it needs the plotter's GPS/GNSS receiver for location information for its DSC. What I have on my 23 WA is a separate, networked antenna receiver, a networked receiver in my HDS-7, and a totally independent handheld Uniden DSC radio that has an internal GPS/GNSS receiver. So, I have two GPS?GNSS receivers on the network and one independent one in the handheld radio; the Link 8 can use either one that's on the network. The hidden Gotcha is that it all depends on the NMEA 2000 network, if I lose its power supply then it all becomes dis-integrated and I'd be dependent on the intergated capabilitiy of the handheld radio.

jimh posted 10-30-2013 08:00 AM ET (US)     Profile for jimh  Send Email to jimh     
Having a hand-held radio on the boat is a good plan. If a boat is capsized, the fixed-mount radio will be useless. A hand-held radio that floats would be a great asset to have in that situation. A hand-held radio with DSC and its own GNSS receiver would be really nice to have in that situation.

As for the radio, if it has a GNSS receiver, then it should be able to display its position on its front panel display. That is about all the radio needs to do. You cannot really expect the radio to have stored charts and be a chart plotter.

I believe at this writing only Standard-Horizon has a fixed-mount radio with an integral GPS. Another big advantage of integration of radio and GPS is the connection between them. The radio manufacturer takes care of that problem for you. As the USA Coast Guard has found out, if you leave it to the boat owner to connect the radio and the GPS, the connection is just not being made in most cases. The biggest advantage of the DSC radio is then lost. It is a strange situation: a DSC radio is now required by FCC regulations. But proper installation is left to the boater, and most boaters are not properly installing the radio. They don't connect it to their GNSS receiver, and in many cases, they do not get an MMSI.

6992WHALER posted 10-30-2013 09:47 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
My Standard Horizon GX1700 VHF radio has a built in GPS receiver. I have programed a FCC issued MMSI number in the unit. Because the GPS data shown on the screen is very rudimentary my main intent is to use this radio for making DSC emergency calls.

My Standard Horizon GX2100 VHF radio with a different Boat US issues MMSI number is talking to my Garmin Chart Plotter. This is the radio that I use for communicating with other vessels using DSC. The ability of the Chart plotter to display the locations of other vessels locations on the chart plotter is very useful.

If I connected my GX1700 to a GPS/Chart plotter (you would have to turn off the radios internal GPS receiver to do this), and the chart plotter failed or the connection between the radio and the chart plotter was broken the Radio would still have the ability to send a DSC message.

So I agree it would be best if all VHF radios had a built in GPS receiver even if they end up being connected to a GPS Chart Plotter. I do not agree that all GPS Chart plotters should have built in radios.

Hoosier posted 10-30-2013 06:25 PM ET (US)     Profile for Hoosier  Send Email to Hoosier     
To sum up this discussion into a few words: if a radio is required to provide DSC services then it has to have an integral GPS/GNSS receiver to provide position information. Duh.
DVollrath posted 10-30-2013 06:50 PM ET (US)     Profile for DVollrath  Send Email to DVollrath     
I guess I'm satisfied with the Link-8 not having a built in GNSS receiver. It's a cost versus capability trade-off that occurs in so many aspects of widget design. I really liked the price of the Link-8 VHF considering it had both the DSC and AIS capability.

In this particular case, the NMEA 2000 network is really simple, and I'm much less concerned about a failure of its power supply in particular, and if the boat power went out the Link-8 would not function either. I think the redundancy of the handheld with an independent power supply is the best situation.

I'd be interested to know what is sent out by the Link-8 during a DSC call if it had been receiving position information but then lost the fix. Does it transmit last known position? That would probably be useful in most situations, but could be very misleading in some. I cannot find anything in the manual about this.


jimh posted 10-30-2013 08:19 PM ET (US)     Profile for jimh  Send Email to jimh     
The radio should hold on to the position data for about four hours. I make that statement based on my observation: if i shut off the chart plotter on my boat (which has the GNSS receiver) about four hours later the radio alarms with a message--"No position data has been received for four hours."

I believe the thinking is a position that is four hours old is better than no position at all. I believe in the DSC message sent there is some indication of how old the position data is.

6992WHALER posted 10-30-2013 08:33 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
My radio acts just like Jim's, at four hours it tells me the position info is more than four hours old. So yes it will still send a position if a DCS call is made but the radio may or may not still be in that location.

I can also hand enter the current position into the radio.

One of the reasons I purchased the Radio with a built in GPS receiver was so I could shut down my Garmin network at night but still maintain current position data in a DSC radio.

jimh posted 10-30-2013 09:47 PM ET (US)     Profile for jimh  Send Email to jimh     
John--That is a good point: if you shut off your chart plotter at night and it has the boat's only GNSS receiver, then you don't have a current position fix in case of an emergency. I typically do shut off my chart plotter at night. I figure its life span is not infinite, so I want to keep the hours down. But that means I have shut off my GNSS receiver, too. (Well, actually, on my chart plotter I only have a GPS-only receiver.)

I like the idea of having a second GNSS receiver, even if a GPS-only receiver, in the radio. It gives the boat a real 24-hour emergency position fix source, and could also be useful as a back-up for the main GNSS receiver if that receiver goes out.

On that Standard-Horizon radio (GX1700) I assume the NMEA output can send the GPS data. Have you connected your radio to any other devices so you can use the GPS data from the radio?

6992WHALER posted 10-30-2013 10:18 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
I have not connected the GX1700 to anything.

I am keeping it as a totally redundant system.

Yes it is capable of communicating GPS data with NMEA output.

Hoosier posted 11-01-2013 02:55 PM ET (US)     Profile for Hoosier  Send Email to Hoosier     
My Uniden MHS135 has a NMEA 0183 output that I could connect to a chartplotter that also has NMEA 2000. I don't know if the chartplotter would then make the Uniden's position data avalable on the N2K network, it'd be pretty cool it it did.
jimh posted 11-02-2013 12:54 AM ET (US)     Profile for jimh  Send Email to jimh     
In my opinion, it would be unusual--if not remarkable--for a device like a chart plotter to automatically translate data it received on its NMEA-0183 input in the form of NMEA-0183 sentences into data on its NMEA-2000 network connection where it would translate the NMEA-0183 sentence into the correct NMEA-2000 parameter group number (PGN) packets. Usually to get this sort of translation between the two protocols you have to purchase a protocol convertor. These protocol convertors sell for about $200, and they have a limited vocabulary of sentences that they know how to translate.

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