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Old 28-08-2019, 01:43   #1
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Second GPS Antenna?

Hi,
I intend connecting an AIS and VHF to my existing chartplotter using NMEA2000 system.
The chartplotter has a GPS antenna connected. Should I connect another GPS antenna to the AIS/VHF? Is it possible they will conflict, or do I leave everything as it is and just connect via NMEA2000?
Thank you for any advice, as I am learning as I go through websites and youtube.


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Old 28-08-2019, 01:47   #2
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Re: Second GPS Antenna?

The AIS needs its own antenna because of very precise timing signals that should not be hampered by other signals on the line. AIS class B emits in the time spaces left open by the class A senders.
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Old 28-08-2019, 03:41   #3
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Re: Second GPS Antenna?

Thanks for your reply.

It seems I have not explained myself properly.
I have purchased a splitter for the VHF and AIS aerial, which is suitable for transceivers.
My question here is related to the GPS antenna only. I hope this explains more clearly.
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Old 28-08-2019, 09:20   #4
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Re: Second GPS Antenna?

If you bought a ais / vhf then you do not need a 2nd gps. Ais transmitters come with a gps antenna and you must use it. That was what the above comment was about. But you do not have an ais transmitter. Not clear on first post. As you said ais and vhf.

Is your chart plotter internal gps or nmea 2000 gps?

If internal it’s handy to have a 2nd one so the vhf can stay on with the plotter off. And not give gps alarms.
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Old 28-08-2019, 09:32   #5
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Re: Second GPS Antenna?

You donít say what model VHF you have but only a few are N2K. Most are 183.

I would connect the VHF in to the chart plotter 183 out. Connect the AIS to N2K
Connect CP to N2K. Your done

The reason for the 183 link to you VHF is to get position data to DSC to function.

Note: the AIS transmit will come with its own GPS antenna, it does not normally broadcast this data on the N2K network. You must use this antenna for AIS to work.
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Old 28-08-2019, 09:53   #6
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Re: Second GPS Antenna?

Im still confused with what you bought. If you bought an ais transmitter. It came with a gps in the box. And you must use it.
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Old 28-08-2019, 13:47   #7
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Re: Second GPS Antenna?

Ok.
VHF is a Lowrance Link6.
The AIS does have an internal gps however it seems that there will be little signal, if any, where I need to mount it (inside the cabin with no direct view of the sky). So I thought I would need to add an additional gps antenna, to ensure DSC and AIS both have a good signal.
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Old 28-08-2019, 14:04   #8
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Re: Second GPS Antenna?

I have both an ais transponder with its own GPS antenna/receiver and a ships GPS antenna/receiver.

I have set the ais transponder to not accept external GPS sentences from the nmea backbone and to not send GPS sentences (from the ais gps) to the backbone.

This prevents a conflict between 2 differing sets of gps sentences and does allow changing the configuration should either the ais gps or ships gps fail.

It is possible to have gps sentences "labeled" something like gps1, gps2 which in theory gives the ability to select which gps sentence source to accept. But I have not had any success with that.

As a side note I do something the same with my depth finder. The main MFD does depth and sends it out to other displays (raymarine st stuff). One of the "repeaters" has a built in depth sounder and its own transducer. That sounder is shut off and only acting as a repeater. If the MFD or its transducer fails I can activate the repeaters sounder and get depth info.
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Old 28-08-2019, 14:30   #9
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Re: Second GPS Antenna?

TwoSkippies,
It appears that you're unware of how the AIS system / AIS transponders work?

And, you've haven't exactly detailed what equipment you have / what your application is?

Regardless....
I'm going to try to help.

Quote:
Originally Posted by Two Skippies View Post
Ok.
VHF is a Lowrance Link6.
The AIS does have an internal gps however it seems that there will be little signal, if any, where I need to mount it (inside the cabin with no direct view of the sky). So I thought I would need to add an additional gps antenna, to ensure DSC and AIS both have a good signal.
1) All AIS transponders (including the Lowrance NAIS-500, that I assume you're equipping with), have a built-in GPS receiver....this is a requirement of the AIS standard (internationally required by all AIS transponders)



AIS transponders must receive their position info from their own internal GPS receiver (whether using an external antenna or one belowdecks)!!
That is how they work!
This has nothing to do with NMEA....whether NMEA0183 / 38400, nor NMEA2000!

The GPS antenna that comes with your AIS transponder, is just that....an antenna! (unlike 99% of our marine GPS "antennas", which are GPS receivers built-into the antenna housing)
The GPS antenna supplied with the AIS transponder is just the antenna....the GPS receiver is built-into the AIS transponder itself...

Having a GPS antenna out in the clear is good....but, the good news is, assuming you have a non-metallic deck, you can certainly mount this GPS antenna just under the deck and you should have good GPS signals / reliable fixes...


2) We are assuming you have:

Lowrance Link 6
https://www.lowrance.com/en-au/lowra...roduct_details




Lowrance NAIS-500
https://www.lowrance.com/en-au/lowra...500--nmea2000/


with this GPS antenna
https://www.lowrance.com/en-au/lowra...f-ais/gps-500/


Lowrance NSPL-500
https://www.lowrance.com/en-au/lowra...-ais/nspl-500/


What "chartplotter" you have??
Well, what ever it is....if it is capable of displaying AIS target info, you will need to connect the NAIS-500 NMEA output to your chartplotter....
(but, this has nothing to do with a "second GPS antenna"...



As for what GPS data to send to your VHF-DSC Radio?
That's your choice....but, I'd recommend sending NMEA position data from the NAIS-500 to your VHF-DSC Radio....that way you have GPS position data on the VHF (for DSC calling, etc.), even without your chartplotter....
{of course, for the past 18 years or so, I've been recommending a separate / dedicated GPS receiver for VHF-DSC and MF/HF-DSC radios....but, I'm assuming you're not interested in any more info/recommendations....just want to know how to connect / use what you have? }


3) I'm still amazed that anyone chooses anything but Vesper for AIS these days?
But, I assume you have your reasons...

Also, please remember that if you do not share the details of what you have, what you are choosing, what your exact application is, etc.....you're not likely to get accurate (nor detailed) answers.



4) BTW, why youtube?
Why not use the radio and AIS manuals?
All the info is there for you...


Hope this helps.


fair winds.


John
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Old 28-08-2019, 14:43   #10
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Re: Second GPS Antenna?

My gps antenna is in the cabin and gets very good signal.
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Old 28-08-2019, 18:51   #11
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Re: Second GPS Antenna?

Just as a point of reference regarding the Camino-101 (which I have):

Milltech Marine says-

Now the folks at AMEC have come up with a new feature that is the best of both worlds. Our very popular AMEC CAMINO-101 Class B AIS transponder can now either use its internal GPS system coupled with the AMEC external antenna or it now supports using an external GPS device connected through the inbound NMEA port. This means that you could use a single input/output NMEA connection with a chartplotter to send AIS data to the chartplotter from the CAMINO-101 and receive GPS data back to the CAMINO from the chartplotter.

Do other transponders allow external antenna? I don't know.
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Old 28-08-2019, 18:58   #12
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Re: Second GPS Antenna?

evm,

Yes, we're aware of this Camino anomaly....it is unique to their unit (and over the past few years, as far as anyone here has ever found, is not IMO acceptable....and therefore shouldn't pass [didn't pass?] IMO certification?)
And, this is why I (and many others) have not discussed this peculiar situation....it just causes confusion....

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Old 28-08-2019, 20:10   #13
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Re: Second GPS Antenna?

The problem with splitting hairs is that hairs are split. Not entirely productive don't you agree?

Quote:
Only AIS devices that are used on SOLAS vessels - Class A transceivers and SARTs - are regulated by the IMO. All other AIS devices are regulated on a nation by nation basis.
I don't try to keep information from folks because I think it might confuse them. Rather I try to inform folks in an effort to bring their understanding up to where it should/could be.
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Old 28-08-2019, 20:46   #14
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Re: Second GPS Antenna?

Quote:
Originally Posted by ka4wja View Post
"Vesper for AIS these days"

I use a Vesper Watch Mate XB-8000. On the open ocean I find it better than radar. Eventually, every vessel will be required to have AIS.
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Old 28-08-2019, 21:25   #15
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Re: Second GPS Antenna?

some units like the vesper do in fact have an internal GPS antenna. and the external antenna is optional if the signal is too weak. the xb 8000 works without it depending on where you mount it.
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