How to send GPS NMEA data to 2 different devices, all different manufacturers?

dutyhog

dutyhog

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High-tech was my work all my life, and as contrast I liked to have most things basic and simple on the boat. So I'm way behind modern navigation. We have an MLR FX412 GPS which outputs NMEA 083 v2 data (RMB & RMC) by 2 wires to an ST60 Multi in the cockpit.

Today I replaced the decades-old analogue VHF with a Standard Horizon GX1200E. It can get NMEA 083 v2 data by 2 wires to display latitude and longitude. I took the output NMEA from the ST60, assuming that it daisychains the full data set that goes into the ST60. But it didn’t.

It looks as though the ST60 NMEA outputs only data that Raymarine generates, and doesn't pass on all the NMEA data from the MLR GPS. If so, can I take the NMEA signal in parallel from the GPS to the ST60 and the new VHF, or is there an official way to daisychain/multiplex it?
 
Nmea works like people (especially males) : one talker may talk to many listeners (but make sure they are all configured to the same baudrate etc.) and any listener can only cope with one talker .regardless of being in a listener group or not.
They are "dot connected".
Check this thread : http://www.ybw.com/forums/showthrea...tial-NMEA-to-Single-Ended&highlight=opto+nmea

ST60 is on a planet of its own...
but it can be made to work.
 
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Oh well, I was probably too optimistic.

I disconnected the Raytheon RT60 and took the NMEA directly, and only, to the connections on the Standard Horizon GX1200E DSC VHF. But there was still no GPS data shown on the radio. Because I haven't activated MMSI, I checked with yaesu.co.uk that it should show such data.

I also tried a good common earth to the radio's NMEA -ve input, with and without the NMEA -ve wire to the radio - no luck (unlike with the Raytheon RT60 repeater).

My multimeter confirms that the signal to +ve input is really positive, and fluctuates rapidly, but I'd need a 'scope to check the waveform and peak voltage. When connected to the Raytheon RT60 repeater it does show the correct data (even with it's -ve input removed), so seems to be proper NMEA 0183 v2. The GPS has been set to just RMC, and RMC plus other sentences that contain lat & long data, but no different result. I wish I had another source of NMEA output to try - maybe this is telling me to buy a Standard Horizon GPS?

When trying the NMEA to both Raytheon RT60 and radio in parallel the RT60 shows data for about a minute then "loses fix". Could it be that the input/output impedances aren't matched well enough (eg there isn't enough current delivered)? I hope I don't need to make up a signal boosting/conditioning circuit.

I'll just use the VHF without DSC, unless a solution emerges.
 
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You need to read the radios handbook carefully re linking(I am going the same way with the same radio) then your gps re.linking.
And thats when it starts to do my head in!
Wheras the radio has four wires my garmin gps just uses two plus as I recall a common earth.
Im just trying to connect the two at the moment fingers crossed but I would like to add a third.
Im also in process of fitting a wifi bridge between my ais engine and various onboard systems.
What fun!
Registering device with offcom is free and online and mmsi is issued immediately.
As you need this for emergency dsc with this radio to work perhaps gps doesnt function on radio without first inputting the mmsi number.
I do know that emergency dsc works without a gps the radio allowing you to manually input a fix but perhaps not without mmsi enabled.
I am going to be spending time next week fitting mine fingers crossed.
 
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dutyhog said:
I disconnected the Raytheon RT60 and took the NMEA directly, and only, to the connections on the Standard Horizon GX1200E DSC VHF. But there was still no GPS data shown on the radio.
Click to expand...

You connected the GPS to the radio's blue and green wires?
 
yaesu.co.uk emailed me that "The radio should show GPS regardless of MMSI installation." I haven't registered for an MMSI number because neither of us crew have done the modern radio course & exam.

For NMEA input to the Standard Horizon GX1200E DSC VHF the blue and green wires are used (page 16 of the book).
Basically I've tried, as their instructions say:
blue to NMEA +ve and green to NMEA -ve
and also tried
blue to NMEA +ve and green to a good common earth (a bus bar close to both radio and GPS, that they both use)
blue to NMEA +ve and green to common earth as well as to NMEA -ve

Gordon

PS - I'm not colour blind either! But maybe someone in the factory is - perhaps I should reverse them?
 
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It's possible the radio's faulty, if your GPS feeds the Raymarine ST60 properly. I guess it would be nice to try the radio with another GPS before returning it.
 
I doubt if there is an electronic fault with it. I suspect Nmea Message data output from the talker are incompatible with the listener. An NMEA message typically contains more than one type of data e.g. a single msg could hold both position and speed. As a result there are lots of message types with position information on. Perhaps the gps is not outputting the message type that the vhf is expecting?

This happened to me - and it took me a lot of soul searching to discover it! I tried to amend my gps to output the message that the vhf was expecting but failed miserably. I caved in by purchasing a new gps unit (a cheap non display 'puck' type) that is only used to supply data to the vhf. Having 2 gps's provides back up if one should fail! Its also actually faster than than the old gps! (I wont tell you about the problem I then had of trying to use the puck to supply position info to other instruments - again ancient ones - again I failed!)
(its also worth noting the mlr is an old device and could also be outputting a different version (nmea version number) of the same message - again an incompatibility issue).

This is all due to the dogs dinner of every manufacturer trying to implement the badly drawn up NMEA standards/protocols of the 80's and 90's.

Perhaps there is some merit in the argument of throwing away all electronic equipment and starting afresh by buying all equipment from the same manufacturer! (But I suspect that 5 years down the line or so you'll be having the same problems when you add a new piece of equipment).

If you do go buying any new kit make sure the new kit doesn't output the message 'optionally' (i.e. ensure its mandatory!) - some equipment (e.g. my cheap puck!) you have to manually boot (by connecting to a pc) every time to switch on the optional message. A right pain in the butt.

So, in summary, welcome to the world on nmea messaging!

And have fun!
 
To understand NMEA 0183 read this. http://www.google.co.uk/url?sa=t&rc...=rNvvAGzWpKfyRqK-H2HOQQ&bvm=bv.92885102,d.ZGU

As others have said there are a number of things that have to be right for NMEA 0183 data transmission to work.
1) There can only be one "talker" but multiple "listeners" in a single circuit.
2) All instruments must be set to the same baud rate.
3) All instruments must be able to send (if the talker) or read if listeners the same sentence format. The manuals for each instrument should tell you which sentences they use. The problem can be unsurmoutable if you have an old instrument which uses a "retired" sentence trying to communicate with a new one that only uses the current format.
 
pvb said:
The OP has said that his GPS outputs RMC, which is what the radio needs.
Click to expand...

okay, both the gps and radio use the RMC nmea msg type. However, I suspect that the gps is outputting the msg to nmea 2.0 whereas the radio is expecting it to be type 2.3. A new parameter was added to the msg (at the end just prior to the checksum) between the 2 versions - see http://www.gpsinformation.org/dale/nmea.htm#2.3. if the radio is expecting it to be 2.3 and it does a match on Checksum to verify that it has received the msg properly then the match will fail.

Perhaps this mismatch is the problem?

This parameter was also added to GLL msg type, but not to GGA and GNS (which the radio can also take) - so perhaps the OP can just output GGA or GNS instead of RMC? This could be an easy fix?
 
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This may not be the issue but it is worth stating anyway. There are two types of nmea0183, balanced and differential. In balanced, neither wire is connected to ground but they 'float' and it is the voltage difference between the two which carries the data. In differential one of the wires is connected to ground. Balanced can normally cope with both versions but it may explain why things stop working when you parallel your st60 and VHF. In balanced systems the wires are normally labelled A and B rather than neg and pos.
 
alteredoutlook said:
okay, both the gps and radio use the RMC nmea msg type. However, I suspect that the gps is outputting the msg to nmea 2.0 whereas the radio is expecting it to be type 2.3. A new parameter was added to the msg (at the end just prior to the checksum) between the 2 versions - see http://www.gpsinformation.org/dale/nmea.htm#2.3. if the radio is expecting it to be 2.3 and it does a match on Checksum to verify that it has received the msg properly then the match will fail.

Perhaps this mismatch is the problem?

This parameter was also added to GLL msg type, but not to GGA and GNS (which the radio can also take) - so perhaps the OP can just output GGA or GNS instead of RMC? This could be an easy fix?
Click to expand...

I don't understand the fervour for increasingly far-fetched theories, when a few seconds on the internet will let you establish that the GX1200E accepts "NMEA0183 version 2.0 or higher".
 
As the OP I'm sorry this has drifted around, albeit interestingly - I've been away for a few days. On return I found a message from yaesu.co.uk with advice that I could never have guessed for connecting these instruments:

MLR FX312 GPS or the MLR FX412 DGPS Navigator
Wiring to GX1200E

FX312/FX412 ..... FX312/FX412 Designation....Standard Horizon Wiring

Blue ..... ...................... - 0 Volt ............................... Black
Red .........................+10 to 36 Volts DC ............ ...... Red
Brown or orange .. Reference RS422 (NMEA OUT)....... not used
Yellow .................. Output RS422 (NMEA OUT)....... not used
Green .................. Reference RS232 .........Green
Black .................. Input RS232 .................. Grey
White.................. Output RS232 ..................Blue

ie connect the RS232 rather than NMEA output from the GPS. I'll try it within a few days. Maybe with the Raytheon needing the "normal" NMEA signal the two outputs will be nicely decoupled. Gordon
 
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alteredoutlook said:
okay, both the gps and radio use the RMC nmea msg type. However, I suspect that the gps is outputting the msg to nmea 2.0 whereas the radio is expecting it to be type 2.3. ...... if the radio is expecting it to be 2.3 and it does a match on Checksum to verify that it has received the msg properly then the match will fail.

Perhaps this mismatch is the problem?
Click to expand...

This radio's instructions do say that it can read version 2.0 or higher, so I didn't doubt that 2.0 would be OK.


This parameter was also added to GLL msg type, but not to GGA and GNS (which the radio can also take) - so perhaps the OP can just output GGA or GNS instead of RMC? This could be an easy fix?
Click to expand...

It also says that "RMC output is recommended" but it's easy to try GGA alone if necessary.
 
RS232 is differential nmea whereas RS422 is balanced, all as referenced in my earlier post. Either should really work as both carry the nmea data.
 
Have recently found that my GPS receiver had given up the ghost.As it was buried somewhere in the depths of a load of glass fibre and to tight to purchase another,tried a different tack.Went into the menu of my Navman plotter and told it to output NMEA.
Connected to my Raymarine plotter and it worked perfectly,instant fix.
Connected it to my ICOM VHF and time/position displayed on screen.
However it will NOT work both at same time.
 
Everything now works - the Raytheon ST60 repeats all data from the MLR GPS (position, speed, XTE etc) and the Standard Horizon GX1200E DSC VHF shows position and time from the GPS.

Many thanks to Sam at yaesu.co.uk - very good customer service - and responders to this item, especially pvb, billjrat and keith-i.

Now I'll get an MMSI number and install it - I think it's sensible (and legal) to have the emergency button functioning fully for anyone to use, even though the usual crew aren't qualified yet for DSC. I think there are courses/exams 100 miles away, so may try them in the winter.

Gordon
 
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