AIS advise

[Fenders]

I have read through all the forums regarding AIS and I am seeking confirmation of my understanding.

I have just fitted a new plotter that can display AIS information.
I am considering installing an AIS receiver.

Would I be able to use the VHF masthead aerial via a splitter or should I instal a separate aerial?

I have been looking at the splitter from Glomex. Seems a fair price.

Also, I have looked at the AIS receiver from NASA.

Thanks

[Symphony]

Better to have its own antenna. Only needs to be on the pushpit as that gives more than enough range and you can also use that in an emergency for your VHF, although I think you will find the NASA uses a non standard plug so you need a converter plug.

[Yngmar]

For a receiver, there is no reason not to go with a splitter. Don't buy new, there are tons of used AIS receivers + VHF splitters popping up on eBay and elsewhere for cheap, as most people these days are upgrading theirs to transceivers.

[sy_Anniina]

I am currently upgrading to from no-AIS to AIS receiver and finding out that it may actually be more cost-efficient to upgrade the old VHF-DSC to VHF-DSC-AIS integrated system (like Lowrance Link-8).

The cost of AIS+splitter or AIS+cable+antenna + the cost of reprogramming MMSI for the DSC from previous owner may exceed the cost of replacing the old VHF with Link-8.

Well - this way I won't have any emergency antenna..

Tommi

[tiger79]

Also, I have looked at the AIS receiver from NASA.

I'd suggest you ignore the Nasa receiver.  It's only a single-channel receiver.  For not much more money you can get a well-built dual-channel parallel receiver, such as the McMurdo Smartfind M15 or the Comar AIS2-NMEA, both around £189.

Rather than a splitter, you could consider a receiver with a built-in splitter, which would be a bit neater to wire up.  The Comar AIS Multi at £249 might appeal.  At only £60 more, it's a similar cost to using a Glomex splitter.

[mikeiso1192]

I am in the process of fitting an AIS transponder and will be going down the route of a separate antenna, on the basis that if my mast top VHF antenna fails for whatever reason; I do have a viable backup.
What I came on here to say was that in my research I recall reading that if you go with a splitter. Then it needs to be AIS compatible. However, that may only apply if you are fitting an AIS transponder as opposed to a receive only unit.
Just my 4p worth.

Mike

[Salty]

I am in the process of fitting an AIS transponder and will be going down the route of a separate antenna, on the basis that if my mast top VHF antenna fails for whatever reason; I do have a viable backup.
What I came on here to say was that in my research I recall reading that if you go with a splitter. Then it needs to be AIS compatible. However, that may only apply if you are fitting an AIS transponder as opposed to a receive only unit.
Just my 4p worth.

Mike

If you go down the route of having a separate antenna for transmitting and receiving AIS signals, remember that there are some recommendations on where it should be located. For example you wouldn't want to have it at the mast head where its proximity to your VHF aerial would mean that transmission on one aerial would likely damage the instrument connected to the other.
If you have the AIS transmitting aerial sited somewhere closer to deck level, it's periodic transmissions could be injurious to humans if within a few metres of them or closer than at least one meter above head height. Also, it is not recommended to have a radar transmitting and receiving aerial at a similar height as your AIS transmitting and receiving aerial. Unfortunately I don't have the specific figures to hand to quote, but the recommendations were according to the information within the installation guide that came with my icom system. So before you make a lasting decision, read up on those recommendations as it may save you spending out on something that you then find you cannot use, and plan where you propose to place the various parts of the system.

[Holger]

I am not a technician and certainly I cannot provide much of a technical explanation. However, about 12 months ago I installed a unit by Weatherdock (EasyAis) which serves quite a number of purposes. I am pretty sure that there are a number of reasons why this is should not be a viable option. Nevertheless, it has worked. The unit I have has a splitter so that I can use the same antenna for AIS and VHF. Also it provides the best radio reception I ever had on this boat (with the same antenna). In addition I can use the same antenna for DVBT(2) reception. Of course, I cannot receive AIS information at the time I use the VHF. Since I own a recreational vessel I understand that may AIS signal is posted when the AIS trasmissions of commercial vessels leave room for it. I went for the WiFi model and now I can see Ais targets on my mobile phone and tablet which is a nice but not an essential option. The device has worked properly during the past 12 months. It is  very comfortable (which includes the manual and the installation) but not cheap.  For the time being, it serves its many purposes. I am not sure whether I this is a suitable device for long distance travelling as I believe the consumption of energy may not the best you can have and there are a number of reasons why systems should be redundant. At this stage of my life I sail mainly coastal waters and estuaries and I enjoy the benefits of this device. This may change. What I want to say is that from my standpoint the answer to your question depends on what you want. If I wanted the most reliable AIS systems I would go for a redundant system with its own antenna and, most likely, I would  have at least two displays working independently from each other. If your question is whether you may use one antenna and a splitter to enjoy AIS the answer, in general, is yes you can.   

[tiger79]

If you have the AIS transmitting aerial sited somewhere closer to deck level, it's periodic transmissions could be injurious to humans if within a few metres of them or closer than at least one meter above head height.

Surely this is unnecessary scaremongering?  AIS Class B transceivers are restricted to a maximum 2W output - less than half of what most of us routinely use on our handheld radios (right next to our heads!).  An AIS transceiver isn't ever going to fry people's brains!

[mikeiso1192]

Interesting comments from you all.
My proposed installation will have the AIS antenna mounted 2.5 meters above the transom on the arch I have supporting my 220w of solar panels.
It's only a "small" antenna and will shade the panels less than the back stay does so shouldn't have any significant effect on charging.

Mike

[Salty]

Further to my posting at 6 above, the separation recommendations in the icom installation manual are as follows
1. If you use a separate antenna for transmission, it should be omni directional, and mounted at least five metres above the main deck where a suitable structure exists. If no suitable structure exists then the bottom of the antenna should be not less than one meter above head height and not less than three meters horizontally away from any human, and where this stated to be in accordance with FCC rules. The five metre distance is based on the FCC Safe Maximum Permissible Exposure (MPE) distance of three metres added to the height of an adult (two metres). They go on to say that for watercraft without suitable structures, that all persons must stay out of the three metre MPE radius. In other words it is not Icom "scaremongering," but is the word of FCC who have nothing to gain by such "scaremongering." Icom acknowledge within their recommendations, that the output power of their transmitter is limited to two watts.
2. Icom, as the manufacturer of the instrument I have fitted, recommend that the AIS transmitting antenna should be located at least three metres away from the radio VHF antenna which rather rules out fitting it at the masthead, though not impossible.
3. They recommend that the VHF AIS antenna is not placed in line with a radar beam and that it is not shaded by the mast.
3. They do not recommend placing the AIS display unit within one metre of the navigation compass.

As far as I am aware the FCC have no jurisdiction within the UK, so those who don't wish to be guided by their rules can presumably do as they wish, though a prudent owner would hopefully have some consideration for the health and safety of all persons onboard.

[tiger79]

Further to my posting at 6 above, the separation recommendations in the icom installation manual are as follows
1. If you use a separate antenna for transmission, it should be omni directional, and mounted at least five metres above the main deck where a suitable structure exists. If no suitable structure exists then the bottom of the antenna should be not less than one meter above head height and not less than three meters horizontally away from any human, and where this stated to be in accordance with FCC rules. The five metre distance is based on the FCC Safe Maximum Permissible Exposure (MPE) distance of three metres added to the height of an adult (two metres). They go on to say that for watercraft without suitable structures, that all persons must stay out of the three metre MPE radius. In other words it is not Icom "scaremongering," but is the word of FCC who have nothing to gain by such "scaremongering." Icom acknowledge within their recommendations, that the output power of their transmitter is limited to two watts.
2. Icom, as the manufacturer of the instrument I have fitted, recommend that the AIS transmitting antenna should be located at least three metres away from the radio VHF antenna which rather rules out fitting it at the masthead, though not impossible.
3. They recommend that the VHF AIS antenna is not placed in line with a radar beam and that it is not shaded by the mast.
3. They do not recommend placing the AIS display unit within one metre of the navigation compass.

As far as I am aware the FCC have no jurisdiction within the UK, so those who don't wish to be guided by their rules can presumably do as they wish, though a prudent owner would hopefully have some consideration for the health and safety of all persons onboard.

The FCC and EC exposure guidelines were drafted by civil servants with little understanding of the reality.  The Icom recommendations you quote also include the warning "In all cases any possible risk depends on the transmitter being activated for long periods. (actual recommendation limits are specified as an average of 6 minutes)".  Now an AIS transponder only transmits for about 26 milliseconds at a time, and only once every few seconds, and at only 2W maximum.  This rather makes a mockery of the caution not to transmit for more than 6 minutes!  And, as I've already mentioned, the risk from using a handheld VHF is far far higher and is accepted by almost all of us.

[IslandAlchemy]

Interesting comments from you all.
My proposed installation will have the AIS antenna mounted 2.5 meters above the transom on the arch I have supporting my 220w of solar panels.
It's only a "small" antenna and will shade the panels less than the back stay does so shouldn't have any significant effect on charging.

Mike

That will work just fine.

[Fenders]

Thanks for all your replies. A very interesting discussion.

I like the idea of the Lowrance Link 8 as mentioned above and it is a fair price.

As my new plotter is a Lowrance I thought it might be more compatible with the Link 8.
However, I have just learnt from the very helpful support team at  Lowrance that I will be unable to connect the 2 and integrate both AIS for the plotter and DSC for the VHF as the plotter can only communicate at one baud rate as it has only one NMEA 0183 port. AIS needs 38400 baud and DSC for the vhf needs 4800 so it is either AIS or DSC.

And since the whole excercise was to provide AIS overlay on my plotter I am now revisiting my plans as follows:

I will keep my old Simrad 68 vhf and connect via an AIS/VHF splitter. The AIS will be fed into the plotter, the vhf into the radio and I will install a gps aerial to connect to the vhf for the purposes of DSC. The new plotter has an integrated aerial.

So it looks like I need to find a suitable gps aerial for the vhf radio as well as a splitter.

I welcome your thoughts on the above and any recommendations regarding aerials.

[tiger79]

What is the model of your plotter?

Which AIS receiver are you buying?

Why do you want a splitter?  Why not have a simple dedicated AIS antenna on the pushpit?

[Fenders]

I have bought a Lowrance Hook 7. It has a built in gps aerial and has one nmea0183 port.

I am considering a NASA AIS engine 3.

My plan is to use the masthead aerial and using a splitter like the Glomex RA 201 I will be able to provide a signal for the vhf and AIS to the plotter via the NASA engine3.

I was also hoping that by connecting the vhf to the plotter I would be able to enable the vhf for the purposes of DSC.

As mentioned above, Lowrance advise me that I would only be able to connect the plotter either for the use of AIS or DSC.

My way around this problem would be to connect the vhf to a gps aerial..

I do not want an AIS display at the chart table.

[tiger79]

OK, firstly, as I suggested earlier, the Nasa AIS engine 3 isn't a good choice.  AIS data is transmitted on 2 frequencies.  Most AIS receivers have a 2-channel receiver which listens to both frequencies simultaneously.  The Nasa product is only a 1-channel receiver, and it alternates between the 2 AIS frequencies.  This means that it can take twice as long to receive AIS data.  With fast-moving commercial shipping, this delay can mean that your AIS display isn't very accurate.  There are much better 2-channel receivers for not much more money.

The Glomex splitter will work.  Many people aren't happy about using splitters on the main VHF, as they can lead to signal degradation.  For less money, you could get a simple stub aerial and mount it on the pushpit to feed the AIS receiver.

To provide GPS data to your VHF, a suitable standalone receiver would be the Evermore SA320, which is around £70.

[Fenders]

Tiger 79

Thank you very much for your advise.

I will go down the path you have suggested.