GPS output connections

[Airborne473]

Hi again, I was chatting to some freinds and they mentioned a problem that they would like some help with.
They tell me that they can connect their GPS o/p to a PC or VHF or Plotter one unit at a time and each works well. But when they try to connect to two or three units at the same time then none of them work.
Not much info other than that mentioned above but wondered if anyone else has had this problem and know of a fix??

 

[savageseadog]

You need a NMEA multiplexer or a repeater

 

[Airborne473]

Thanks Savage, had an idea that a GPS couldnt really service more than one peice of gear without something to spread the signals. Now I need tio start looking for a multiplexer so that i can go back and earn a few beers from them

 

[thomashoebus]

Is this true? I think it depends on the kind and number of instruments you connect. I have my vhf, autopilot and navtex connected to my gps which is a simple garmin handheld 72. Everythinhg works fine. (without a multiplexer)

Probably it goes wrong when you connect the gps to a pc and then add other equipments.

Here is what i found about it on the net:
"Whilst the output from an NMEA device can be split to drive several others, eventually the signal becomes too weak and the data does not get through. This is increasingly common with the more complex systems found on larger yachts and in commercial installations. An NMEA Booster increases the signal strength, allowing a greater number of devices to be connected."

 

[R32Stbrigid]

You probably DONT need a multiplexer. Most GPS units will support several "listeners". Garmin state up to three, but I have exceeded this - 5 currently, with no problems. A multiplexer is used to combine several "talkers".

 

[tome]

NMEA outputs should be able to support up to 10 listener devices. You do not need a multiplexer nor repeater

The problem is probably due to 1 or more of the listeners being connected the wrong way round. Get 1 piece of equipment working first, then attach the next. If the first stops working, reverse the connections on the new listener - continue until all are working

Some listeners have a common ground and only need a single wire connection. If they comply with the strict NMEA standard, they should be isolated and then require 2 wires. If you only have a single wire output to drive it you will need to connect the negative of the input side to ships negative

 

[Danny]

Could also be due to earth loop problems and the resultant noise generated. If you are using shielded twisted pair connecting cables then it's probably best to only have the shield connected to earth at one point and this should be at the GPS.

 

[davierobb]

I use a small Garamin gps to feed vhf, repeater and laptop, all work ok with no data corrutions at all. Get the connections right use good quality connectors and cable and you should be ok. I recon I'm pushing it at three units but it works reliably. Using an nmea repeater is neater but they cost and are just another thing to go wrong.