What antenna for NASA AIS?

[justonemoreproject]

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

[sailingdog]

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

[justonemoreproject]

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

[rikhall]

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

[T37SOLARE]

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

[sailingdog]

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

[justonemoreproject]

Originally Posted by rikhall

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

[ecsimonson]

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

Originally Posted by rikhall

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.

[goboatingnow]

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.

[sailingdog]

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. 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.

Originally Posted by goboatingnow

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.