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View Poll Results: Want to have an AIS transponder or only see others how have?
Yes 53 86.89%
No 8 13.11%
Voters: 61. You may not vote on this poll

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Old 30-10-2011, 10:36   #61
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I sometimes have trouble grasping the concept that big ships should see me........I work really hard at watching out for them , and staying the hell out of their way ! Not sure how knowing that my boat shows up on the screen of a ship that will take three miles to stop or is not likely to be able to turn in a narrow channel does any more than give the watch commander on that boat something to laugh about with his crew. "" look at that idiot in the sailboat trying to beat us across the channel , hope he makes it "". I have a receive only SH GX 2150 overlayed on my garmin chart plotter and I love it. Years of riding a motorcycle has instilled a "" you never have the right of way"" mind set , and I have never been run over on a motorcycle . Spent two weeks in the San Juan islands buddy boating with a friend who had the latest greatest raymarine setup on his boat , and I constantly could see all the commercial traffic , and only see him sometimes , even when we were rafted together. No clue wether the problem was his or mine , only know I didn't see him a lot of the time.......I am very happy with the ability to see the big ships , and stay out of the way of the folks who are trying to make a living on the water. Guess I just have a simple mind.
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Old 30-10-2011, 10:37   #62
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Re: AIS Transponder: Yes or No

In my experience ships radars do pick up small objects.

They have greater resolution, more power, their antennas are higher, work on both 10cm and 3cm and their filters are better than yacht radars.

Hail commercial vessels on 13 and you have a much better chance of getting a response than if you call on 16.

I monitor 13 and 16 all the time but many commercial vessels do not pay much attention to 16 and some no attention to 16. I monitor 14 (VTS for SF Bay) only when I am checked in.
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Old 30-10-2011, 10:39   #63
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Re: AIS Transponder: Yes or No

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Originally Posted by Auspicious View Post
Sure. I'll give them a ring on Monday. I'd like to hear what they have to say. There is simply no difference between an "AIS VHF" antenna and a conventional marine VHF antenna. There is no match difference. It simply doesn't work that way.
Ok. Tell me what the difference is because in my experience there is some sort of reason why a specific AIS VHF antenna is necessary for my hardware (Furuno FA150). I am curious to know as well.
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Old 30-10-2011, 11:03   #64
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Re: AIS Transponder: Yes or No

I really do not understand the question in the poll. What is it meant to ask? Can a Mod edit it?
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Old 30-10-2011, 11:07   #65
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Re: AIS Transponder: Yes or No

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I really do not understand the question in the poll. What is it meant to ask? Can a Mod edit it?
Whether or not an AIS transponder is useful for a pleasure boat.

Being 65 posts into the thread, it's kinda late to change anything.
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Old 30-10-2011, 11:13   #66
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Re: AIS Transponder: Yes or No

I have the Raymarine AIS500 integrated splitter - vhf aerial to AIS - AIS to VHF.
Integrates with Raymarine screens.
Used first time this passage - is terrific complementary addition to nav/safety gear.
Very enlightening to see speeds/sizes etc of ships.
I agree with others that it is one thing to get info on ships - can see them anyway - but would be better if could get info on smaller vessels.
Perhaps it will become mandatory for pleasure vessels too...
Watches are almost exclusively to look for smaller sailboats - with no/low wattage lights.
I say get both/integrated be seem - don't get run over...
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Old 30-10-2011, 12:01   #67
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Re: AIS Transponder: Yes or No

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Originally Posted by Auspicious View Post
Sure. I'll give them a ring on Monday. I'd like to hear what they have to say. There is simply no difference between an "AIS VHF" antenna and a conventional marine VHF antenna. There is no match difference. It simply doesn't work that way.
Actually there can be quite a difference in antennas. We have a network analyzer and have characterized a number of different antennas from various manufacturers. AIS-tuned antennas are designed with their center frequency at about 162 MHz. I just tested one a few days ago and it measures 1.125:1 VSWR at 162 MHz. An excellent result. A normal VHF is typically centered around 156 MHz. I've tested some of those that have >4:1 VSWR at 162 MHz and so they are wholly unsuitable for use with AIS.

However, many ordinary VHF antennas do have enough bandwidth to be under 2:1 VSWR at 162 MHz. Standard VHF antennas likely won't be optimal, but in practice there is nothing wrong at all with using one, if it has adequate bandwidth.

You can check the VSWR plots from the antenna manufacturer or ask them for the center frequency and the bandwidth.

This is an important subject, because in my experience the most common problem people have with Class B AIS transponder installations is the antenna system. It is sometimes the antenna not being suitable, but most often it is the cables/connectors or even placement of the antenna too near other antennas, masts, radars, etc. This might explain why an earlier post said they had a friend tied alongside and couldn't receive them.

(FYI disclosure: I work for Vesper Marine - manufacturer of Class B AIS equipment)
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Old 30-10-2011, 12:16   #68
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Re: AIS Transponder: Yes or No

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I did.

Vis-a-vis three online ais viewers we can see all 'B' vessels displayed.

Can't say if they meet Class B requirements but can say this one works as advertised.

Cheers,
b.
An empirical test is good of course, but you can't tell what you aren't seeing. I'm sure these units do what they say, but because they aren't type-approved they don't have to say anything other than "AIS receiver". So are they as good as a type-approved Class B?

A few years ago I lab tested one and it had good sensitivity but a high packet error rate. In practice, this means that messages would be dropped. Of course, AIS repeats the transmission a short time later, so hopefully the message would be picked up the next time.
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Old 30-10-2011, 13:27   #69
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Re: AIS Transponder: Yes or No

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Originally Posted by jeffrobbins View Post
Actually there can be quite a difference in antennas. We have a network analyzer and have characterized a number of different antennas from various manufacturers. AIS-tuned antennas are designed with their center frequency at about 162 MHz. I just tested one a few days ago and it measures 1.125:1 VSWR at 162 MHz. An excellent result. A normal VHF is typically centered around 156 MHz. I've tested some of those that have >4:1 VSWR at 162 MHz and so they are wholly unsuitable for use with AIS.

However, many ordinary VHF antennas do have enough bandwidth to be under 2:1 VSWR at 162 MHz. Standard VHF antennas likely won't be optimal, but in practice there is nothing wrong at all with using one, if it has adequate bandwidth.

You can check the VSWR plots from the antenna manufacturer or ask them for the center frequency and the bandwidth.

This is an important subject, because in my experience the most common problem people have with Class B AIS transponder installations is the antenna system. It is sometimes the antenna not being suitable, but most often it is the cables/connectors or even placement of the antenna too near other antennas, masts, radars, etc. This might explain why an earlier post said they had a friend tied alongside and couldn't receive them.

(FYI disclosure: I work for Vesper Marine - manufacturer of Class B AIS equipment)
Thanks very much for this post, it's very helpful. Can you tell me about what you've found on the opposite roles? How good is an AIS antenna at the extreme frequencies of VHF?

My working theory is to use the AIS as a backup voice antenna in an emergency. I'd just as soon have a 'optimized' AIS and 'ok' vhf in an emergency. But if the AIS antenna will truncate 16 so badly as to limit the range down to like 5 miles then I'd rather have poorer everyday AIS performance and a good standby VHF capability.
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Old 30-10-2011, 14:40   #70
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Re: AIS Transponder: Yes or No

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Originally Posted by xymotic View Post
Thanks very much for this post, it's very helpful. Can you tell me about what you've found on the opposite roles? How good is an AIS antenna at the extreme frequencies of VHF?

My working theory is to use the AIS as a backup voice antenna in an emergency. I'd just as soon have a 'optimized' AIS and 'ok' vhf in an emergency. But if the AIS antenna will truncate 16 so badly as to limit the range down to like 5 miles then I'd rather have poorer everyday AIS performance and a good standby VHF capability.
That's why I analyzed this particular antenna last week. We are considering using it for a large commercial project where the intention is primarily as an AIS antenna but also as a VHF backup.

It has a VSWR of 1.125:1 at 162 MHz and 1.8:1 at 156 Mhz. As a result, it is very well suited for AIS and the slightly higher VSWR at 156 won't make any real difference, especially with the higher power output of a VHF radio. So it wouldn't need to be reserved just for emergencies. I think it would be fine as an everyday antenna.

I've also recently had a look at the specs of a few AIS mast-head style antennas with the idea of using them via a splitter for both AIS & VHF. The specs for the ones I've looked at all look similar to the one above.
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Old 30-10-2011, 15:35   #71
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Re: AIS Transponder: Yes or No

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Originally Posted by xymotic View Post
Thanks very much for this post, it's very helpful. Can you tell me about what you've found on the opposite roles? How good is an AIS antenna at the extreme frequencies of VHF?

My working theory is to use the AIS as a backup voice antenna in an emergency. I'd just as soon have a 'optimized' AIS and 'ok' vhf in an emergency. But if the AIS antenna will truncate 16 so badly as to limit the range down to like 5 miles then I'd rather have poorer everyday AIS performance and a good standby VHF capability.
I'd rather have a dedicated, properly sized AIS antenna and a separate VHF antenna. I presume any VHF antenna or AIS antenna would serve in a pinch, but if the base unit went out, I could easily mate my 6 watt handheld into the masthead coax, and get enough height to likely get over the horizon.

AIS is critical in a smaller radius than VHF...and RADAR for that matter. While I would like the ability to reach a port captain from 12 miles out, if I can see traffic via RADAR at 16, I could wait for the AIS to ID them at 8 NM and still have plenty of reaction time. So the separate AIS antenna could go on the same pole as the wind generator if there aren't RF issues, or I could just run two VHF cables up to the masthead. Not a biggie either way. Splitters don't really make sense to me, because the key to avoiding problems with damp and corrosion is not to cut the cables in the first place.
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Old 30-10-2011, 15:39   #72
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Re: AIS Transponder: Yes or No

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I've also recently had a look at the specs of a few AIS mast-head style antennas with the idea of using them via a splitter for both AIS & VHF. The specs for the ones I've looked at all look similar to the one above.
Again, because I carry and use handhelds far more than VHF, and because I'll have a SSB rig as well, I think I'd just have two antennas optimized for AIS...I could conceivably carry a spare full wave VHF antenna (it's only six feet) up the topping lift or backstay.
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Old 30-10-2011, 15:41   #73
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Re: AIS Transponder: Yes or No

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I'd rather have a dedicated, properly sized AIS antenna and a separate VHF antenna. I presume any VHF antenna or AIS antenna would serve in a pinch, but if the base unit went out, I could easily mate my 6 watt handheld into the masthead coax, and get enough height to likely get over the horizon.

AIS is critical in a smaller radius than VHF...and RADAR for that matter. While I would like the ability to reach a port captain from 12 miles out, if I can see traffic via RADAR at 16, I could wait for the AIS to ID them at 8 NM and still have plenty of reaction time. So the separate AIS antenna could go on the same pole as the wind generator if there aren't RF issues, or I could just run two VHF cables up to the masthead. Not a biggie either way. Splitters don't really make sense to me, because the key to avoiding problems with damp and corrosion is not to cut the cables in the first place.

This is what I'm talking about. I'd have AIS on the Mizzen and VHF on the main, and have the ability to swap them (for troubleshooting *OR* emergency use.)

And jeff please name names on antenna specifics you can send me a pm if you desire but I think it'd be really helpful
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Old 30-10-2011, 15:52   #74
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Re: AIS Transponder: Yes or No

My AIS antenna is on the aft rail. It works just fine for my purposes. I sail coastal in a busy area and don't worry about what's over the horizon.

If I was planning to cross oceans I'd want more height, but (within 50 miles of the coast) if the swells are going to be so big my signal doesn't get out then I'm not leaving port.
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Old 30-10-2011, 16:26   #75
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Re: AIS Transponder: Yes or No

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Thanks very much for this post, it's very helpful. Can you tell me about what you've found on the opposite roles? How good is an AIS antenna at the extreme frequencies of VHF?
We're only talking about a little over 5 MHz bandwidth. It's a pretty sorry VHF antenna that won't deliver a VSWR below 2:1 over the marine VHF band. Let's not forget that the two AIS channels are VHF Channels 87B and 88B. This is in-band stuff people.

It would be a pretty sorry AIS transponder that can't transmit into a VSWR below 2:1.

I'll report back after I call Furono tomorrow.
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