ghostlymoron
Well-Known Member
On a system with SH plotter, garmin gps 128, AIS and DSC radio, is it possible to have a single antenna? Also can the antenna be mounted inside the cabin?
Sharing GPS antenna
- Thread starter ghostlymoron
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Vara
Well-Known Member
My set up has SH plotter with integral aerial, GPS data is then fed from that to the radio and anything else that needs it using NMAE output.
On previous system, all three aerials were mounted inside with no discernible drop in reception. (Fibreglass boat with teak decks.).
Don't think that you can directly split the output from an aerial though, might be worth trying with a cheapo eBay aerial.
On previous system, all three aerials were mounted inside with no discernible drop in reception. (Fibreglass boat with teak decks.).
Don't think that you can directly split the output from an aerial though, might be worth trying with a cheapo eBay aerial.
ghostlymoron
Well-Known Member
The AIS has nmea output so maybe best to connect antenna to that and feed position to other units via nmea info.
RIBW
Well-Known Member
Without knowledge of the specific SH, AIS & DSC, how about, at its simplest:-
A single (internally mounted) GPS antenna to the Garmin128, which split feeds NMEA Lat/Lon to the SH & DSC at 4800baud.
Depending on the SH CP, it should have a 2nd input to take AIS at NMEA 38400baud.
Or, are you trying to do something more complicated?
Cheers
Bob
ghostlymoron
Well-Known Member
No, nothing complicated. Just not sure if nmea output can be connected to multiple receivers.
David2452
Well-Known Member
The official line is 1 talker to a max of three listeners, it may work with more but it will work reliably and consistently with three, use twisted pair shielded cable for the interface and RF groung the shield at the talker end only.
knuterikt
Well-Known Member
AIS transponder require its own directly connected GPS.
savageseadog
Well-Known Member
If you're talking about and analogue GPS aerial then no. NMEA will be OK.
nimbusgb
Well-Known Member
That's as maybe but it can still be shared.
An aerial and a GPS receiver are not quite the same thing although the terms are being used interchangeably these days.
An aerlal outputs RF signals, a receiver usually outputs the signal in some other format after it's been processed. So Nmea for a boat GPS receiver or USB serial data for a puck type system.
David2452
Well-Known Member
It might work, but without a dedicated stand alone GPS receiver it would lose it's type approval, they should have their own.
lw395
Well-Known Member
This may be the case.
The AIS may 'talk' to the GPS as well as listen, in order to control what the GPS sends back.
It's possible for GPS modules to be set to send data more frequently with different data included or not sent for instance.
Like just sending the position twice a second instead of once.
I don't currently know whether this is the case for any particular AIS, but the only true answer is to RTFM.
As for connecting two GPS receivers to one aerial, that can be done, but you need to ensure that only one is feeding 5V to the aerial.
Obviously the other GPS won't work if the one powering the aerial is off.
And you need a splitter good at 1575MHz of course.
Having the aerial indoors may work brilliantly for years then let you down in rough weather when you most need it.
I consider it a very poor idea if you're going to rely on GPS.
ithet
Well-Known Member
If you a talking about the SH GPS arial, then it is an active type - and IS itself a GPS receiver that outputs NMEA 183 sentences. SH can provide information on how to attach listeners and power to it. But it will not be able to drive the Garmin 128 this way.
ghostlymoron
Well-Known Member
Could the AIS send position info to garmin by nmea?
RIBW
Well-Known Member
I have one AIS (Receiver) that can forward LAT/LON that it has received from another source because it includes a NMEA mux. The other (receiver) won't - it receives RF and sends out target NMEA info only. Alternatively, as mentioned earlier an AIS transponder (transmit & receive) will need a GPS source, depending on the manufacturer, it may be able to forward LAT/LON. But why? My garmin 128 has its own antenna - its purpose is to generate a LAT/LON amongst other things. It doesn't need a GPS (LAT/LON) input.
I have one GPS 'antenna' that outputs Seatalk, another that produces only the RF signal and a third that provides NMEA LAT/LON.
Because there are so many equipment variants (e.g. some DSC radios have in-built GPS and AIS receivers), you could have more targetted input, if you specified the equipment you have and what you are trying to do with it.
All the best
Bob
bitbaltic
Well-Known Member
I have a system with two Garmin 128s. In my experience the 128 will output, but not listen to, NMEA0183. They 'listen' only to garmin propreitary sentances so you have to set each into 'garmin/garmin' (send/receive) mode in order to push waypoints and routes between them. There is no function (that I am aware of) for getting them to listen to real-time position sentances in either garmin/garmin or any kind of NMEA0183. Each unit needs an antenna feed and to do the raw decoding to get position information.
So, the short answer is probably no, your 128 will not listen to NMEA position sentances originating from the AIS.
That the garmins would not listen to NMEA0183 position data was news to me after I installed them because that was exactly what I had planned on having them do as I wanted one to be a cockpit repeater only. Consequently I had to split the feed from the (passive) rail antenna. This was no problem at all with a decent soldered joint and both units work fine.
As for the question about whether you can use a single rail GPS antenna, as RIBW has said it would be helpful if you told us exactly what the other components of your system are. If (as has been suggested) either your plotter or AIS transponder uses either an active rail GPS antenna or an integral GPS, you will not be able to simply split the feed from a single rail aerial between them and the 128 which requires a passive antenna.
If you want to aggregate your position data to minimise aerials on the rail then you are probably going to have to go down the route of driving everything via NMEA0183 outputted by the Garmin, because I think the overall limiting factor will probably be that the 128 is not likely to listen to the NMEA output from anything else in your system. You will have no problem getting a single 128 to 'talk' to four or five 'listners', so this would not be a limitation. Whether the other kit will successfully 'listen' to it and whether it is a good idea (especially for an AIS transponder) is another question.
Hope this helps
Cheers
lw395
Well-Known Member
I think people are using the phrase 'active antenna' or 'passive antenna' to mean two different things.
Most GPS antennas, at least those that run on a cable longer than 6 inches are 'active' in that they contain a low noise amplifier and some filters. These need 3 to 5 V.
An antenna with integrated receiver which outputs NMEA is rather more than an 'active antenna' in my book, you might call it a masthead receiver or integrated antenna-receiver.
A passive antenna in my book has no amplification, like a VHF antenna or TV aerial.
You can get passive GPS antennas, but they generally need to be connected directly to the input of the receiver, as there is no budget for cable loss.
I've only ever managed to transfer waypoint lists from one GPS to another via a PC. I think there is an NMEA sentence for current waypoint name and coords, but if the Garmin doesn't read it, then it's hard to make one be a repeater of the other.
bitbaltic
Well-Known Member
Okey Dokey. As you say integrated or non integrated antennas are what we should be talking about.
Yes I think the problem is not that the sentances don't exist in the NMEA standard but that the Garmin is an old unit (mine says 'copyright 1997-2001' on boot!) and either that it predates the relevant part of the standard or that Garmin didn't anticipate any need for the 128 to listen to external position info when they designed it.
Cheers
ghostlymoron
Well-Known Member
Bitbaltic, the aim is indeed to reduce the amount of clutter on the pulpit.
ghostlymoron
Well-Known Member
Thanks all I think I need to be more specific so have gathered the info on all installed units which are:-
Garmin GPS120XL, external antenna
Icom M411 VHF Transeiver
Vesper Marine AIS Transponder external antenna
Standard Horizon CP180 external antenna
Does this help?
Garmin GPS120XL, external antenna
Icom M411 VHF Transeiver
Vesper Marine AIS Transponder external antenna
Standard Horizon CP180 external antenna
Does this help?
RIBW
Well-Known Member
Hi, Thanks for the extra detail; here is a quick first reaction, which will need checking.
It makes some assumptions which opinions will differ on!!!
Dump the (old) Garmin - The CP180 will provide most if not all you get from the Garmin. We keep ours because it is handy/local for completing the log book entry. Another reason to keep it might be to minimise power consumption when sailing by turning off the AIS and CP.
A cursory glance at the AIS spec indicates it will provide AIS & GLL to the CP180 which eliminates the need for the CP180 to have its own GPS 'Antenna'.
I haven't looked at the ICOM spec but I don't expect it to care where it gets GLL from?
Hope this helps
BobView attachment 43951
