NMEA Connections

JackFrobisher

JackFrobisher

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I've done a search and read what I can find about NMEA interface talkers and listeners and I've read mixed messages about the number of listeners that may be served by a talker. Some say no more than three, others "several".

Has anyone any definitive experience of how many listeners can be supported, particularly by a Garmin 45 GPS? I'm thinking of a DSC radio (ICOM M421), a basic Furuno radar, a Yeoman plotter and a laptop (via serial port). It's probable that the Yeoman and the Laptop will not be used at the same time, but they might, making it 4 at once ...
 
Short answer is I'm not sure. However have you looked at the radio closely ? My NAVMAN DSC radio has a NMEA in and a NMEA out, i.e. I can connect the GPS to the radio input and then the radio output to a cockpit repeater. I am presuming that the radio will output a "full strength" signal ?

If that isn;'t the case you can buy a NMEA "buffer" ( in other words an amplifier ) from these guys : web page ( scroll down right to the bottom of the page ).
 
I used a Garmin 48 connected to navtex, radio, nasa repeater and sometimes laptop/autohelm.
all will work together.
 
There have been several threads over the years relating strange problems when trying to connect multiple listeners to a single talker. It seems that it is entirely dependent on the particular combination of instruments you are using - so the only real answer is to try it and see.

I suspect you may have issues with what you suggest - particularly trying to combine the laptop (RS232) with a genuine NMEA listener.
 
The definitive text in the standard (NMEA 0183) states "The number of listeners depends on the output capability and input drive requirements of individual devices"

However, it goes on to recommend that talkers conform with the EIA-422 specification while sourcing not less than 15mA and that listeners shall not sink more than 2mA

The practical upshot is that conforming talkers should be able to drive at least 7 conforming listeners. You shouldn't have any problems with 4 listeners and won't need a buffer
 
The Yeoman and PC may not like each other as they have talk as well as listen on NMEA ... this is where conflict comes.

BUT you can use your PC to PASSTHROUGH ... that is - it rec'vs NMEA and on a different port can output NMEA to another item such as autopilot / radio etc.

NMEA is a simple protocol and you can even test connections ...

Some may advise Multiplexers etc. - forget them - they are a waste of money .... simple screw block terminals is all thats needed ... 4 - 5 items connected is not unusual ...

So way to go ... wire up GPS ... have terminal block connected and ready to connect items to ... connect each one by one and check results ... as each works - connect next ... etc. You'll probably end up with all connected and wondering what all the fuss is about !!
 
[ QUOTE ]
The Yeoman and PC may not like each other as they have talk as well as listen on NMEA ... this is where conflict comes.

Some may advise Multiplexers etc. - forget them - they are a waste of money

[/ QUOTE ]

Steady on ole chap - multiplexers are required when connecting more than 1 talker together, and would resolve the Yeoman/PC conflict you mention. They are only a waste of money if not required...
 
Re: NMEA Connections .... ok ol bean ...

Maybe I was a bit rash there ... yes in serious conflicts of Talkers - that is what Multiplexers are there for to stop the conflict.

But Tome - you read as well as I do ---- the number of times in the past people have recc'd them when absolutely THEY havent understood what they are and also are totally not necessary.

I stand corrected on this one !! /forums/images/graemlins/wink.gif
 
I have used an old Garmin (75 I think ) which output to a Raymarine 2000 Wheel pilot, a Yeoman plotter, AIS radar and a DSC VHF all at once with no problem. I now use a Navman 5505 plotter to do the same, still OK. Local electronics seller reckoned problems only occur with Raymarine GPS which have limited output.
 
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