AIS/VHF question

I just replaced my old VHF radio with a new Garmin VHF/AIS receiver. Also replaced a Raymarine chart plotter with Garmin MFD7610. I planned to use the existing antenna but after looking at it decided that the cable was starting to fray and the whip was showing signs of deteriorating. Replaced with a new antenna from West Marine. The VHF owners manual says connect to VHF antenna but nothing about a splitter or separate AIS or GPS antenna. Everything works fine but did not test it for any loss. It currently uses the internal GPS from the MFD. Perhaps there is some loss with this arrangement but it seems to work for me.

Delfin said:

That would be an advantage. However, I've found that off shore, the odd ship you encounter frequently doesn't respond to VHF, and in shore other boats only sometimes do.

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Therein you'll see advantage with AIS since you will be able to hail the ship with its name. It seems they are far less likely to ignore a hail by name than by "ship off my port bow".



One advantage of the dedicated antenna is that it's tuned for AIS rather than the whole VHF spectrum. Higher is better, I noticed a significant improvement when I changed to the AIS-tuned antenna and moved it to the masthead.

If at all possible, I would use two separate antennas. You will get better performance, and have fewer things to fail. But I understand the realities of adding stuff, especially cable runs .....

twistedtree said:

If at all possible, I would use two separate antennas. You will get better performance, and have fewer things to fail. But I understand the realities of adding stuff, especially cable runs .....

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Anything is possible and if I see degradation I'll bite the bullet. But I'm curious what "degradation" will look like. Wouldn't you need a comparative range experiment or is it obvious with increased static or something concrete?

Sure, that would work.

The receive losses are advertised as quite small. As far a performance issues, the primary one is the ability to VHF transmit the same time as AIS transmit. You can't. The AIS connection is lost when VHF power is sensed. The models I've read do have the VHF com as the priority.

But if you just have an AIS receiver, in a VHF radio, then the single antenna should be no problem since you are not transmitting AIS.

Delfin said:

Anything is possible and if I see degradation I'll bite the bullet. But I'm curious what "degradation" will look like. Wouldn't you need a comparative range experiment or is it obvious with increased static or something concrete?

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Yes, it’s nebulous. I just figure if I can eliminate possible issues, I like to do it. But I have suffered through enough exercises in pulling cables that I can hardly criticize anyone using a splitter. I used on on our tender when I added AIS because there wasn’t really space for a second antenna. And it’s so low to begin with....

I have a Raymarine AIS650 transceiver with a separate antenna. As stated here separation of antennas is important. My AIS antenna is a Shakespeare. They recommend at least a 4ft separation.

twistedtree said:

Yes, it’s nebulous. I just figure if I can eliminate possible issues, I like to do it. But I have suffered through enough exercises in pulling cables that I can hardly criticize anyone using a splitter. I used on on our tender when I added AIS because there wasn’t really space for a second antenna. And it’s so low to begin with....

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We installed the Sitex Metadata AIS transceiver and fancy splitter. We were able to use the cable for a dedicated GPS that was attached to a backup Simrad GPS, so that was simple. I was able to pick up targets around 40 miles out, which seems pretty good. According to the tech, the Sitex splitter, which costs about as much as the transceiver, handles the hand off between VHF and AIS seamlessly, at least in his experience. We'll see...

Maerin said:

Therein you'll see advantage with AIS since you will be able to hail the ship with its name. It seems they are far less likely to ignore a hail by name than by "ship off my port bow".


.

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Assuming the other vessel has AIS or the radio on.

On my boat, my mechanic installed the new VHF for the new AIS as far from the VHF antenna as possible (about 10 feet). Both AIS and VHF are working very well. I was not tempted to go the splitter route; I would rather spend more money for better reliability/function.

Spinner said:

On my boat, my mechanic installed the new VHF for the new AIS as far from the VHF antenna as possible (about 10 feet). Both AIS and VHF are working very well. I was not tempted to go the splitter route; I would rather spend more money for better reliability/function.

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If I'm picking up AIS targets 40 miles away, with the city of Anacortes between me and the target, what would improved functionally look like?

Simi 60 said:

Assuming the other vessel has AIS or the radio on.

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Way off shore, it seems like less than half the vessels encountered have their radios on, or if they do, are paying attention. If we cross over to Hawaii next year, I'm looking forward to a source of info on other large boats that doesn't require that someone be awake on the bridge on those boats.

Delfin said:

Way off shore, it seems like less than half the vessels encountered have their radios on, or if they do, are paying attention. If we cross over to Hawaii next year, I'm looking forward to a source of info on other large boats that doesn't require that someone be awake on the bridge on those boats.

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I don't understand what you are saying.
You've called boats off shore by name and they don't respond?

As far as degradation, it's hard to tell, what the real effect is in a subjective way.
In that you can't tell what you're not seeing or who is not hearing you.

Wxx3 said:

I don't understand what you are saying.
You've called boats off shore by name and they don't respond?

As far as degradation, it's hard to tell, what the real effect is in a subjective way.
In that you can't tell what you're not seeing or who is not hearing you.

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It's been a few years, but between here and Hawaii, I think I hailed around 4 tankers/freighters encountered, and was a bit freaked out by the fact that they didn't return the call. This was pre AIS, so I had no way of knowing the vessel name, but given the fact that we were a long way from land with no other vessels around, I don't think they thought I was calling someone else. I just don't think anyone was on the bridge or bothering to respond to a little sailboat.

You're right on the quantifying an unknown, but I'll do a test today with the CG with and without the AIS connected to the VHF antenna to see what my VHF signal strength is.

Curious, but when you are off shore, what is the max distance you are able to pick up AIS targets?

Delfin said:

If I'm picking up AIS targets 40 miles away, with the city of Anacortes between me and the target, what would improved functionally look like?

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That is excellent reception. I'd be very happy with that.

Hmm, I don’t know!

"According to the tech, the Sitex splitter, which costs about as much as the transceiver, handles the hand off between VHF and AIS seamlessly".

Delfin, this has been my experience with the Sitex splitter as well.

Delfin said:

Way off shore, it seems like less than half the vessels encountered have their radios on, or if they do, are paying attention. If we cross over to Hawaii next year, I'm looking forward to a source of info on other large boats that doesn't require that someone be awake on the bridge on those boats.

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I had the same travelling the south pacific in our previous boat.
Only saw a few but no response from any of them.

How many languages did u try?[emoji51]

Delfin said:

Way off shore, it seems like less than half the vessels encountered have their radios on, or if they do, are paying attention. If we cross over to Hawaii next year, I'm looking forward to a source of info on other large boats that doesn't require that someone be awake on the bridge on those boats.

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Are you trying them on 13? They seem to monitor that more often than 16. Also, I’ve had a few times where the reply was significantly delayed, my assumption being they had to go find/wake up someone who speaks English.

I’ve had an AIS transponder on the last three boats, and I know the big boys can see me. I had one divert several miles to come “check on me” because I was just drifting around without a working engine and no wind (note that I own a powerboat now...)

My sailboat had a splitter so the AIS shared the masthead antenna, and with that height I could see large commercial traffic’s Class A transponders almost a hundred miles away. When I did the Hawaii thing, I was shocked at how much traffic there was. It’s definitely not an empty ocean.

Josh

For those who don't know, commercial boats transmit AIS at 25 Watts. Pleasure boats transmit at 2 watts. You might see them, but they might not always see you.

Gordon

questionmark said:

Are you trying them on 13? They seem to monitor that more often than 16. Also, I’ve had a few times where the reply was significantly delayed, my assumption being they had to go find/wake up someone who speaks English.

I’ve had an AIS transponder on the last three boats, and I know the big boys can see me. I had one divert several miles to come “check on me” because I was just drifting around without a working engine and no wind (note that I own a powerboat now...)

My sailboat had a splitter so the AIS shared the masthead antenna, and with that height I could see large commercial traffic’s Class A transponders almost a hundred miles away. When I did the Hawaii thing, I was shocked at how much traffic there was. It’s definitely not an empty ocean.

Josh

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I assumed it was a language issue as well, and not being rude. I haven't taken the boat out of the slip since I installed the AIS, but I expect that when I don't have an island between me and far away targets range will increase, but even 40 miles certainly seems enough. Later today I'll do some testing on VHF signal strength to see if I can quantity signal degradation on VHF transmission, if any.

diver dave said:

How many languages did u try?[emoji51]

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I tried english and schoolboy French, making the assumption they were fishing vessels from New Caledonia.
I could have given a very basic version of Bislama a try as well.

Impressive. You must have already know that the random chance of a Bislama speaker at the helm is 7.5billion to 10,000.

Since I am only a native speaker of English and Gibberish, I can't count on my Bislama skills for communication.

I tested VHF reception with USCG today and while I am not sure how definitive the results are, they did say that they heard me loud and clear both with the AIS connected to the VHF antenna and not connected. Connected, there is no interruption of the AIS signal that I could see, since it appears to be buffered in some way. In any case, the shared antenna does seem to at least not be any kind of an obvious problem.

Again, thanks for everyone's input!

Delfin said:

If I'm picking up AIS targets 40 miles away, with the city of Anacortes between me and the target, what would improved functionally look like?

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The issue isn’t receiving AIS targets. It’s how it “transceives” and can others vessels pick up your signal. Class B units broadcast at 2 watts, which means that anything that degrades the sending signal affects whether vessels are able to receive and interpret your signal. The issues I had with my Sitex unit related to this issue.

The vessels you are able to identify from 40 miles are likely class A (broadcasting at 12.5 watts) and have the unit on a high mast and therefore increasing the range (freighters, etc.). The range from which your Class B signal can be identified will be considerably less.

Jim

Further to this, from Wikipedia, (assumption it is correct, but...?)

“Class B transceivers are smaller, simpler and lower cost than Class A transceivers. Each consists of one VHF transmitter, two VHF Carrier Sense Time Division Multiple Access (CSTDMA) receivers, both alternating as the VHF Digital Selective Calling (DSC) receiver, and a GPS active antenna. Although the data output format supports heading information, in general units are not interfaced to a compass, so this data is seldom transmitted. Output is the standard AIS data stream at 38.400 kbit/s, as RS232 and/or NMEA formats. To prevent overloading of the available bandwidth, transmission power is restricted to 2 W, giving a range of about 5–10 mi.”

JDCAVE said:

The issue isn’t receiving AIS targets. It’s how it “transceives” and can others vessels pick up your signal. Class B units broadcast at 2 watts, which means that anything that degrades the sending signal affects whether vessels are able to receive and interpret your signal. The issues I had with my Sitex unit related to this issue.

The vessels you are able to identify from 40 miles are likely class A (broadcasting at 12.5 watts) and have the unit on a high mast and therefore increasing the range (freighters, etc.). The range from which your Class B signal can be identified will be considerably less.

Jim

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The distant target was a class A.

I'm not sure I care whether other vessels can "see" me at 10 miles, 5 miles or 2 miles. I've already set the filter to exclude class B units, since I'm not sure I need to clutter my display with info on a Nordic Tug 20 miles away. The purpose of the install, at least for me, is to be able to get data on course and speed of large vessels off shore. 2 watts is the power of a smart phone, so even with some degradation (if any) those that care about data on my little putt putt s/b be able to get it when I am still some distance away.