AIS antenna

[dMAC]

My boat has all Raymarine equipment including the E 90 chart plotter plus radar.

I am thinking about installing a Raymarine AIS transceiver. Should I install a separate antenna or is their any downside sharing the VHF antenna?

[Panache5000]

The new raymarine ais transp requires a dediated ant. Not having a multiplexer as used with he older type.

Better with own ant. No performance loss on vhf.

Seperate ant gives redundancy as spare vhf ant.

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[PlumBob]

Originally Posted by Panache5000

The new raymarine ais transp requires a dediated ant. Seperate ant gives redundancy as spare vhf ant.

For the AIS antenna, is there any reason it needs to be at the masthead? Seems to me that it could be mounted lower down, or perhaps on an antenna pole at the transom, without affecting the gathering of AIS data. For a spare VHF communications antenna, yes, perhaps, but for AIS, no..

Thoughts?

[transmitterdan]

Originally Posted by dMAC

My boat has all Raymarine equipment including the E 90 chart plotter plus radar.



I am thinking about installing a Raymarine AIS transceiver. Should I install a separate antenna or is their any downside sharing the VHF antenna?

Raymarine are selling a unit made by Em-Trak. Em-Trak make a splitter that can use your existing VHF antenna. Contact Em-Trak or Raymarine if you are unsure what exactly you need.

Someone will pop on after this post railing about how AIS antenna splitters are no good or worse; the spawn of Satan. The Em-Trak unit has good specifications and will not degrade your VHF noticeably. It is not cheap however.

The GPS antenna supplied has to connect to the AIS.

[Panache5000]

Correct. The ais as well as vhf work on line of sight.
Obviously the higher the better. My ais ant is installed on the aft end of the boat, +- 2metre high.
I get ais target info on average from 15 to 20Nm.

General note: The raymarine ais transponder interphases well with the rest of the raymar equipment MFD chart plotter/radar etc.
To me the ais transponder is the most vital and best piece of safety equipment on board.


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[DotDun]

Originally Posted by transmitterdan

Raymarine are selling a unit made by Em-Trak..

That's interesting, I thought both Em-Trak and Raymarine were made by SRT.

[MickBeth50]

hi,

i have a raymarine system (from chartplotter to wind depth, VHF and radar)...but was persuaded to by a garmin 600 AIS...it has a built in antenna splitter...it requires a dedicated GPS antenna...i did everything my self and it works well with the e95 chartplotter.

mike

[chuckr]

can only tell you what works for us --

we run raymarine but before raymarine had an ais we got a acr one and installed and it feeds our c70 chartplotter and has for the past 4/5 years or so -- we put on seperate antenna as we believe that each should do it own function -- we have helped a couple of boats with vhf problems in the past and each time they had ais going through their vhf antenna and it just did not work well -- understand they made a number of improvements but we still believe each should stand on it's own

as for mounting we put ours on the bimini between our solar panels and on the other side we put on it's own gps -- redundent? yep

we have used it all over the caribbean from west to east - crossing the atlantic and now in the med -- i mean how far out do want to look? depending on where we are going we usually run our chartplotter on 24nm which is 12nm in front of us and more on the side - we can quickly determine if we will have an issue or not - sometime we run at 12nm and still we can see out 6nm and make a quick determination on if we are going to have an issue --
if you are going to talk to the boat in question they may not even respond until they are closer anyway -

[transmitterdan]

Originally Posted by DotDun

That's interesting, I thought both Em-Trak and Raymarine were made by SRT.

I think you are right. SRT make AIS guts for several OEMs as I understand. But I don't think you can buy from SRT direct.

[Dockhead]

Originally Posted by PlumBob

For the AIS antenna, is there any reason it needs to be at the masthead? Seems to me that it could be mounted lower down, or perhaps on an antenna pole at the transom, without affecting the gathering of AIS data. For a spare VHF communications antenna, yes, perhaps, but for AIS, no..

Thoughts?

I use a Diamond UHF/VHF ham radio antenna on my first spreader, for AIS and UHF/VHF ham work. It works great -- receive AIS targets from up to 100 miles away.

[PlumBob]

Originally Posted by Dockhead

I use a Diamond UHF/VHF ham radio antenna on my first spreader, for AIS and UHF/VHF ham work. It works great -- receive AIS targets from up to 100 miles away.

BINGO! That's what I'll do (or something very similar ;-) ) Thanks for that tip!

[continuouswave]

The AIS transceiver antenna should be mounted with the same consideration for height as any VHF Marine Band radio antenna, that is, higher is better.

The AIS antenna should be cut for or tuned for the AIS channels specifically. The AIS channels are at 162-MHz. A normal ship's VHF radio only transmits between 156 to 157-MHz. The typical marina antenna cut or tuned for a VHF Marine Band radio will not have good VSWR at 162-MHz, and the AIS transmitter may refuse to transmit into a high VSWR.

SRT is the OEM maker of many chips, circuit boards, and complete AIS units. em-trak is their house brand. Many AIS products are private label brands made by SRT. The ones that are not are AMEC and VESPER.

For a brief summary of AIS Class B transponders showing which are SRT derivatives and which are not see

continuousWave: Whaler: Reference: AIS Class-B Transponder Round Up

[Dockhead]

Originally Posted by continuouswave

The AIS transceiver antenna should be mounted with the same consideration for height as any VHF Marine Band radio antenna, that is, higher is better.

The AIS antenna should be cut for or tuned for the AIS channels specifically. The AIS channels are at 162-MHz. A normal ship's VHF radio only transmits between 156 to 157-MHz. The typical marina antenna cut or tuned for a VHF Marine Band radio will not have good VSWR at 162-MHz, and the AIS transmitter may refuse to transmit into a high VSWR.

All true in theory, but in practice the Diamond VHF/UHF antenna works fine with my AIS transponder (also works fine with my marine VHF transceiver). VSWR is about 2.0, which is good enough.

I would certainly agree that for someone who only needs an antenna for AIS, it is much better to go with an antenna specifically cut for AIS, but if you also need a VHF ham radio antenna, then I would, on the contrary, combine these functions in one antenna rather than having that many more cables in my mast and finding another place for an antenna. Which is what I did with good success.


As to height -- VHF is sort of line-of-sight, so higher antenna should give more range. But you don't typically need more than 20 miles for AIS, and even mounting the antenna on the pushpit (which many people do) will usually give you more than enough range when you are exchanging AIS data with ships over their high antennas. With my antenna mounted 10 meters above the water on my first spreader (about 33 feet), I often see ships more than 100 miles away. So more height than that would be entirely superfluous for my use.

A good example of divergence of theory and practice.

[continuouswave]

Originally Posted by Dockhead

VSWR is about 2.0, which is good enough.

A VSWR of 2:1 is generally tolerated by most modern transmitters.

It is hard to extrapolate your particular installation of AIS transceiver and antenna to mean that all VHF Marine Band antennas cut for standard frequency operation and all AIS transceivers will work properly together.