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Old 23-09-2017, 13:20   #1
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AIS antenna

I currently have AIS receive thru my chart plotter and networked with my VHS. I have purchased a class b transponder and would like to like to know if I need separate VHS and gps antennas or whether I can use splitters to my existing vhf and gps antennas. I prefer to keep my receive configuration and just add the transponder , bug am unsure what antennas I would need.
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Old 23-09-2017, 14:04   #2
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Re: AIS antenna

The instructions will tell you and it's different for different brands. Read the instructions.
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Old 23-09-2017, 14:18   #3
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Re: AIS antenna

IIRC, all transponders have their own built in GPS receivers. They may or may not require an external antenna, depending on where they are installed and on the demands of the specific unit. Splitting will not work for the gps portion. However, splitters can work well for the VHF tx/rx part. The best ones, like the Vesper unit, have built in preamps which compensate for any insertion losses. We are using a Vesper and with our masthead standard VHF antenna get excellent range of reception (typically 40+ miles with normal conditions) and have had reports of being received at as much as 15 miles.

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Old 23-09-2017, 14:38   #4
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Re: AIS antenna

You can't use a splitter on the GPS function of a class B AIS unit. You will have to get an additional antenna for the AIS unit only.

At least they are cheap.
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Old 24-09-2017, 05:01   #5
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Re: AIS antenna

Thank for reply. The instructions for the ACR brand transponder state an antenna fir vhf is required, but also mention using a proper splitter with existing vhf radio antenna. A good splitter is about as much as an antenna so pros and cons? The unit has an internal antenna for gps, but I will likely need to mount the unit inside boat with not a clear view of sky for reception. I also see many options for various gps antennas and wonder how good (cost) is required for adequate reception?
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Old 24-09-2017, 05:28   #6
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Re: AIS antenna

You don't have to use a splitter on the VHF function. The thing is that not every boat has two good VHF mounting spots. It wants to be somewhere between the masthead and around 10ft up. It also has to be well clear of any radome. On the other hand the GPS mushroom can be mounted on deck.
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Old 24-09-2017, 06:36   #7
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Re: AIS antenna

If you keep your current configuration, your boat will show up as a dangerous target. Don't know if there is a way to get your chartplotter to ignore it.
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Old 24-09-2017, 08:44   #8
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Re: AIS antenna

Kinda what I thought. I believe I can turn off the receive AIS from the VHS and then tie both the receive and transmit function if the AIS transponder into the men's 2000 backbone in place now which would then have it tied into both vhf and chart plotter.
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Old 24-09-2017, 09:26   #9
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Re: AIS antenna

I would keep your AIS and VHF antennas separate for the sake of reliability and simplicity. That is how I have mine.
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Old 24-09-2017, 09:48   #10
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Re: AIS antenna

Quote:
Originally Posted by hikersailor View Post
Kinda what I thought. I believe I can turn off the receive AIS from the VHS and then tie both the receive and transmit function if the AIS transponder into the men's 2000 backbone in place now which would then have it tied into both vhf and chart plotter.
Your post doesn't quite make sense. It seems to be saying that you want to connect the VHF transmit function to the NEMA 2000 backbone cable. That won't work.

There should be a jack on the AIS box for a cable that allows you to connect to the boat's network so you can overlay the AIS info onto the chart. Not every GPS screen has this function and not every one accepts NEMA 2000 format data from an AIS. The more expensive ones offer you a choice between 00 and 83. Here's an example of a unit that can connect to any network.

NAIS 500 AIS | Simrad Marine Electronics
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Old 24-09-2017, 10:01   #11
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Re: AIS antenna

Quote:
Originally Posted by hikersailor View Post
Thank for reply. The instructions for the ACR brand transponder state an antenna fir vhf is required, but also mention using a proper splitter with existing vhf radio antenna. A good splitter is about as much as an antenna so pros and cons? ...............
A splitter makes the VHF antenna a little less efficient for transmitting (and receiving) VHF signals so that's the "con". A separate antenna for the AIS is better but it's an additional antenna that has to be installed and in some cases put down for bridge clearance.

You can use a short (3') antenna for the AIS if that suits your boat better.
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Old 24-09-2017, 13:09   #12
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Re: AIS antenna

Thanks for the inputs. I think since I have lots of real estate on a catamaran sailboat I might be better off with separate antennas for vhf and AIS. As many boats use these devices it amazes me somewhat that there is this amount of confusion on what should be a simplistic undertaking. I will follow up with a call to Raymarine to see what they have to say.
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