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Discussion Starter #1
Hi,
Has anyone installed this unit on their boat? If so, what antenna (how long) are you using and how well is it working? I am going to do a stern rail mount, but don't know what length antenna to use. Si-Tex sells the same unit and they call it AIS Radar. I called them, but the guy I spoke with didn't know much. He just wanted to sell me something.

Thanks for your input.

Larry
 

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Telstar 28
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AIS works on VHF frequencies... so you need a VHF antenna for it.
 

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Discussion Starter #3
VHF antenna

Sorry not to have specified VHF, but yes, I would like to know what VHF antenna others have used for their AIS antennas / How long, what brand and price if anyone known.

Thanks again
 

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old guy :)
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Larry

I have had the SR161 AIS receiver ($189.00) for a couple of years now. Used a little "rubber ducky" antenna inside the boat the first summer - gave me a four or five mile range. I have it connected to my laptop running FUGAWI ENC version.

Two summers ago I ordered a new VHF antenna for the mastheaad and mounted the old VHF antenna off the radar on the stern. Got 15 - 20 mile range - WAY more than I needed but was good anyway.

For our sailing (east coast of Canada and coast of Maine) we would not be without an AIS receiver. The radar tells me there is something out there, the AIS tells me who, their call sign, how big they are, where they are going, how fast etc etc etc. It is so nice to be able to call that blip in the radar by name and share our mutual intentions.

Good luck with yours.

Cheers
 

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Tartan 37C
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From what I've researched the best option is using a splitter/switch on your masthead antenna. Something like this:



Shakespeare Marine Electronics and Data Systems - StyleAS-2

This automatic switch toggles two radios to one antenna. When you key the microphone on one of the radios, it switches the antenna to it… automatically. The radio stays locked onto the antenna until the automatic switch detects a transmit from the other radio. Easy!

* Specifications:
o Frequency Range: up to 600 MHz
o VSR: Below 1.2:1
o Power Rating: 30 W
o Impedance: 50 ohms
o Connections: SO-239 type
o Power Supply: 12 vDC @ 200 ma
o Sensing/Switching Time: Less than 100 ms
 

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Telstar 28
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I'd recommend a separate VHF antenna for the AiS unit.
 

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Discussion Starter #7
Tell me more about that antenna

Larry

I have had the SR161 AIS receiver ($189.00) for a couple of years now. Used a little "rubber ducky" antenna inside the boat the first summer - gave me a four or five mile range. I have it connected to my laptop running FUGAWI ENC version.

Two summers ago I ordered a new VHF antenna for the mastheaad and mounted the old VHF antenna off the radar on the stern. Got 15 - 20 mile range - WAY more than I needed but was good anyway.

For our sailing (east coast of Canada and coast of Maine) we would not be without an AIS receiver. The radar tells me there is something out there, the AIS tells me who, their call sign, how big they are, where they are going, how fast etc etc etc. It is so nice to be able to call that blip in the radar by name and share our mutual intentions.

Good luck with yours.

Cheers
Thanks for your informaiton. Tahts great that you were able to get 15-20 miles off the stern rail. I've read that the distance an AIS can receive is limited by the height of the antenna and the height of the broadcasting vessel. I read that an 8 foot stern rail antenna and an 88 foot bridge on a container ship will only give 7 miles of reciptioni, which does not seem right at all.
How tall is the stern rail antenna and what brand/db, is the antenna you are using with the AIS?

Thanks - Larry
 

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not a rail mount
not sure how much that increases distance though

Two summers ago I ordered a new VHF antenna for the mastheaad and mounted the old VHF antenna off the radar on the stern. Got 15 - 20 mile range - WAY more than I needed but was good anyway.
 

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Nearly an Old Salt
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use a splitter off teh main masthead VHF antenna, given that the VHF is used very little on a typical boat, the split antenna feed is a good compromise. Like all antennas height is best.
 

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Telstar 28
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First, does the NASA AIS broadcast or only receive. IF it only receives, then it won't be able to use a Coax Splitter/Switch, since it can't "key" the mic.

Second, if the NASA AIS does broadcast, how often does it do so, and for how long. If it regularly broadcasts, it is very likely that your VHF won't be monitoring Channel 16, or any other channel at all, since it effectively won't be connected to an antenna most of the time, since the AIS is periodically broadcasting.

Also, I am willing to bet that the splitter/switch is more expensive than a decent 3 dB gain 3' VHF antenna would be. Having the second antenna means you have a backup antenna in the event you lose the primary VHF antenna. Redundancy in communications equipment is never a bad thing, especially when bad things are happening.

Yes, a VHF is not used very much to transmit, but that doesn't take into account its need to be able to receive transmissions. With a switch it may not be able to.

Finally, height is nice, but not really necessary. The primary use of an AIS unit on a small sailboat is to get information about large ships around you. It isn't to broadcast your AIS information to them, since any AIS used on a small sailboat is likely to be a Class B transciever, and most likely will be filtered out at the big boat's end anyways... so a fairly low antenna will generally suffice. Even a low, cabin top mounted antenna will generally give you a receive range of five miles or more—which is plenty for AIS, since most small boats don't have a screen that will show anything more in any detail.

You really have to think out the unintended consequences that might occur by trying to use equipment you really don't understand. :rolleyes: A splitter/switch is great for two VHF sets... since at least one VHF set will be able to receive at a given time, but not so good when one of the two devices is a special purpose device like an AIS transceiver.

use a splitter off teh main masthead VHF antenna, given that the VHF is used very little on a typical boat, the split antenna feed is a good compromise. Like all antennas height is best.
 

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Discussion Starter #11
Splitter vs. antenna

You are a wise pooch Sailor Dog. You are right that I really don't understand the vagaries of VHF. Got a question for you. Is 6db better then 3d and how long should the stern mounted rail be? Finally, what constitutes a "good 3db antenna". I was looking at a 6db, 8' Shakespeare for 40 bucks. Model 5101 to be exact. There is a huge variation in prices for antennas and I really don't know what makes one better then the next.

Marine Antennas - VHF, SSB, GPS, Satellite Radio, Weather - - SHAKESPEARE VHF 8FT 5101 6DB

Thanks again for the assist.

Larry
 

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There is a ton of bad informaiton in this thread, and I'm not sure where you're getting "NASA" AIS. The National AIS" system is a USCG acquisition to set up numerous sensors, transmitters, and frequency management strategies to provide seamless AIS coverage for the US and its territories.

Here's the link: USCG: Nationwide Automatic Identification System (NAIS)

Coverage will not be limited to line-of-sight. Towers, data buoys, and satellites will be used to achieve seamless coverage well offshore. The goal is 2000 nautical miles.
 

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Nearly an Old Salt
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Sailerdog A bit more research on the the AIS market and its products. Firstly there are a number of splitters deigned for AIS receivers such as VHF Antenna Splitter from Milltech Marine the nasa unit is a receive unit and there are splitters that feed the signal to both AIS receivers and VHF units. The big advantage is that you can use the mast head antenna that spends most of its time doing nothing. Height aows you to see around obstacles like headlands. Early warning of ships that radar or other means of ID cant see is one of the biggest advantages of AIS Height is always good. you should be able to get AIS from 30 miles from the masthead and the more early warning the better

Redundancy is a seperate argument, in practice the event that wipes out your masthead antenna will probably do lots of other damage all of which will means that AIS will be the last thing on your mind.

Sure carry a emergency VHF antenna, but the splitter is a better solution in my experence. See AIS targets from over the visible horizon is fantastic. ( especially with modern shipd going at 20 knots)

Your comments re class B AIS transceivers are incorrect. Again splitters can used that give priority to the VHF transmit. Both AIS and VHF are listening as before so AIS and DSC VHF will function as normal. BTW most big ships dont switch off class B ( as there is little of it around at the moment, even in Europe where its been available for nearly 2 years) the fact is they dont have AIS recievers that can see class B , its only modern class A that can also recieve B. Youre concerns may be teh case in a full implementation class B future but not now.

PS OP the gain should be low or unity gain for an AIS receiver. The 3db and 6db is for transmit

BTW CSmojo NASA is a UK manufacturer of AIS receivers and other fine kit
 

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Telstar 28
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Gobo-

I'm talking about the splitter that was referenced in post #5 specifically. It is not designed for AIS. Yes, there are AIS specific splitters, that avoid most of the problems I've mentioned... but they're not what I was discussing.

The statement about antenna redundancy was for VHF use, not AIS use—if you had bothered to read what I had actually written.
 

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Discussion Starter #15
Thank-you for your replies. Not only have I learned a lot about AIS, but hopefully others will benefit from this thread as well. Especially as more and more sailors install AIS on their boats.

I don't know what unity or low gain is. For the sake of clarity and in the event that I choose to have a stern mounted antenna could someone give the specs and or a specific model of antenna that would work well as a separate stern mount application?

Regarding NASA and AIS splitters:
NASA equipment is made in the UK. I purchased my NASA AIS from AllGadgets in the UK. I chose it because it is a stand-alone unit that uses very little energy as opposed to using AIS engine in conjunction with a lap top. I saved about 250.00 by purchasing from AllGadjets. In the US, the NASA is sold under the Si-Tex label for about 550.00 AllGadgets also sell an AIS splitter for around 130.00.
I believe the Mill Tech one is 150.00. But I will probably get one from them because shipping and handling is about 30.00 from the UK.

Again, thanks for all your input and if anyone has anything else to ad, please chime in.

Larry
 

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Nearly an Old Salt
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Larry, any normal VHF whip can be used get the lowest gain one typically 3db there no use in having a high gain as its used in receive only mode. SO anything from a rubber duck antenna to a 8' antenna can be used. There are supposed specific AIS antennas , where the antenna is tuned to the specific AIS receive frequency, but I suspect its specmanship and unneccessary

The other advantage of a splitter is that you dont have to wire the to the dedicated AIS antenna, The whole thing can be fitted in the control panel near the vhf



The statement about antenna redundancy was for VHF use, not AIS use—if you had bothered to read what I had actually written.
whatsnt taking issue with the original point, merely a comment that redundancy arguments can be overdone. It can be difficult to forsee what gets wiped out. and as I said sure carry an emergency VHf antenna, just dont mount it as you never know what event occurs to wipe out what antenna, irrespective of where its mounted
 

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Telstar 28
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The other problem with high-gain antenna is that they tend to have a fairly flat disc-like reception area...which doesn't work very well on sailboats that heel.
 

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old guy :)
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I've read that the distance an AIS can receive is limited by the height of the antenna and the height of the broadcasting vessel. I read that an 8 foot stern rail antenna and an 88 foot bridge on a container ship will only give 7 miles of reception, which does not seem right at all.

That actually is the "line of sight" distance but we know from experience that VHF does go farther than line of sight. And seven miles is a long distance - certainly long enough to establish communications if you want and plenty long enough to avoid physical contact.


How tall is the stern rail antenna and what brand/db, is the antenna you are using with the AIS?

I think the antenna was about 3 metres above the water. It was an old "Shakespear" type of 3 or 5 dB typical masthead sailboat antenna.

Thanks - Larry
Also - remember - it is for receive only. And, with a seven or eight inch rubber ducky antenna inside the boat I was still getting a couple of miles range or more. Other than the "for the fun of it" value, I cannot see needing more than five or six miles range. Unless you sail a very fast boat!

The "for the fun of it" came when we were at anchor - picking up signals, seeing what boats they were and then Googling them to read all about them. Saw some really neat inside pics of the "yacht" owned by the owner of the Miami Dolphins!
 

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old guy :)
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Sorry - my error:

I said "That actually is the "line of sight" distance " and that is not correct.

Looking at the VHF/UHF Line of Sight Distance Calculator I see:

Total Antenna Height of 1st Station = 10 feet
Total Antenna Height of 2nd Station = 88 feet

For the 1st station, the Radio Horizon is 4 miles away.
For the 2nd station, the Radio Horizon is 13 miles away.
The total line of sight distance is 17 Miles.

Again - sorry - I click too fast, should have checked my data.

Cheers
 

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Nearly an Old Salt
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The point is using the masthead antenna gives upto 30 miles reception. Its always better to have "the option" of distance rather then not. for example fast ferries at 40knots cover 5 miles very very fast
 
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