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Old 24-04-2012, 22:04   #16
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Re: AIS Antenna

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Originally Posted by fairbank56 View Post
Originally, there were 28 marine channels spaced 50Khz apart. Eventually, demand for more channels increased and 28 more channels were added between the original ones so the spacing became 25Khz. Channels 29 thru 59 were designated for land mobile so the new marine channels began at channel 60. Channels in the 60 to 88 range are 60 channels higher than the channel just below it in frequency, i.e. channel 68 (156.425Khz) is just above channel 8 (156.400Khz). Two of the channels, 75 and 76, are never used because they are adjacent to channel 16 in frequency. This is to help prevent interference to channel 16.

Eric
Thanks for that, Eric! I've often wondered how the sorta odd frequency allocations came to be.

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Old 24-04-2012, 22:07   #17
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Re: AIS Antenna

The answers I am seeing is it depends on the AIS transceiver. My Furuno FA-150 would receive but not transmit with a standard VHF antenna. It took an antenna designated as a AIS transceiver antenna for mine to work. Furuno did not have an answer as to why this is the case with their transceiver.
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Old 24-04-2012, 22:27   #18
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Re: AIS Antenna

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Originally Posted by evm1024 View Post
Drats! that's what assuming increasing ch number leads to increasing freq will get you. (Ah, nice to see that someone is reading and understands what I was saying)

I wonder what the history if ch assignments is.

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Quote:
Originally Posted by fairbank56 View Post
Originally, there were 28 marine channels spaced 50Khz apart. Eventually, demand for more channels increased and 28 more channels were added between the original ones so the spacing became 25Khz. Channels 29 thru 59 were designated for land mobile so the new marine channels began at channel 60. Channels in the 60 to 88 range are 60 channels higher than the channel just below it in frequency, i.e. channel 68 (156.425Khz) is just above channel 8 (156.400Khz). Two of the channels, 75 and 76, are never used because they are adjacent to channel 16 in frequency. This is to help prevent interference to channel 16.

Eric
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Originally Posted by Jim Cate View Post
Thanks for that, Eric! I've often wondered how the sorta odd frequency allocations came to be.

73,

Jim
Shameless thread drift ahead -
As weird as channel designators and frequency allocations are in the comms world of radio, I defy anyone to rationally explain the international channel and frequency allocations for television services. To me, they look like a random mass of numbers, bands and frequencies.

BTW, I much prefer the aviation system, no channels, just frequencies! Someone must have assumed pilots and controllers were intelligent enough to real numbers.

OK, rant over, back to AIS antennas.
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Old 21-08-2016, 22:17   #19
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Re: AIS Antenna

Using regular vhf radio antenna on AIS Class B Transceiver, one could see AIS target as far away as 25nm or more. Would that target be able to see you?
Any idea any one?
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Old 21-08-2016, 23:51   #20
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Re: AIS Antenna

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Originally Posted by trantor12020 View Post
Using regular vhf radio antenna on AIS Class B Transceiver, one could see AIS target as far away as 25nm or more. Would that target be able to see you?
Any idea any one?
The answer is "Possibly, but probably not."

Were you receiving a Class-A signal? Those transmit at 25 watts, while a Class-B puts out 3 watts. Class-A generally transmits farther than Class-B. Both generally get line-of-sight performance, but Class-A usually does better.

The typical range for a Class-B signal is six miles minimum, perhaps twice that fairly often. However, under some radio propagation conditions both A and B signals can go hundreds or thousands of miles. While this is interesting when it happens, you can hardly depend on this type of range.
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Old 21-08-2016, 23:57   #21
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Re: AIS Antenna

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The answer is "Possibly, but probably not."

Were you receiving a Class-A signal? Those transmit at 25 watts, while a Class-B puts out 3 watts. Class-A generally transmits farther than Class-B. Both generally get line-of-sight performance, but Class-A usually does better.

The typical range for a Class-B signal is six miles minimum, perhaps twice that fairly often. However, under some radio propagation conditions both A and B signals can go hundreds or thousands of miles. While this is interesting when it happens, you can hardly depend on this type of range.
Paul, Thank you. I didn't realise Class B Tx at lower power. Now that you mentioned it, things are clearer.
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Old 22-08-2016, 00:23   #22
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Re: AIS Antenna

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Originally Posted by Jim Cate View Post
G'Day John,

Don't get your knickers in a knot over this!! Our AIS antenna is our normal VHF whip, a not very top end item, further hampered by both using a splitter (built into our ICOM AIS rx) and being mounted on our radar/solar arch, about 12 feet above the WL.

Despite these handicaps, we routinely get AIS data from 25 mile distances. Frankly, info from greater range than that isn't of much interest to me.

Save your money for something important!

Cheers,

Jim

PS: Extra bandwidth??? The AIS signal is on one of the normal VHF frequencies, and "extra bandwidth" isn't required. Sounds like a sales gimmick to me!
Mark has a "little bit of a point" (from a theoretical point of view) since the 2 AIS frequencies are around 162 Mhz so a standard marine VHF antenna is tuned for frequencies a bit lower but for RX of AIS signals this is really insignificant. I have a dedicated AIS-RX antenna (standard Glomex SS whip) with its base only 2m above sea level and it works very well with also reception of signals > 20NM away.

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Old 22-08-2016, 01:03   #23
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Re: AIS Antenna

We use our rather ordinary VHF aerial, mast mounted, with a splitter at the instrument panel. We pick up AIS from commercial shipping typically about 45 miles out, and often to 60-70 miles (if it is a big cargo vessel), so I don't think you need anything fancy
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Old 22-08-2016, 02:09   #24
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Re: AIS Antenna

One way to check the performance of Class B is to go into marinetraffic.com

Filter out everything but 'pleasure craft'

Select an area with a fair bit of yacht traffic... in the example I used the approaches to the English Channel.

Pick a yacht... any yacht.

Check her details... in there you will find what shore station is monitoring her.... locate station on map.... check distance from shore station to yacht.

My research tends to indicate that power output is not an issue in reception distance... height of antenna on both tx and rx station yes... power output no....

an example AIS Vessel Tracking - AIS Positions Maps | AIS Marine Traffic
( this link may be time sensitive.)

And also... previous research has shown class b has no problem being picked up by the satellites....
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Old 22-08-2016, 14:30   #25
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Re: AIS Antenna

I had to buy a new antenna since I did not want to use a splitter and got a GAM antenna. It came with a nice little chart showing antenna length compared with frequency.
With these steps:
1) Remove the radiating element with a hex key.
2) Cut 3/4 of an inch off the bottom.
3) Reinsert the radiating element.
4) Tighten the hex screw.

Different but related question. When comparing distance with height of antenna, is it the bottom, center or top of the antenna for the height? I mounted mine to the dingy davits, base 7 feet off the water, top is 10 ft off.
I am not too worried about targets 100 miles away, just the ones between me and the horizon.
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Old 22-08-2016, 15:18   #26
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Re: AIS Antenna

I initially set up a vesper marine transceiver and an antenna splitter for the mast-top VHF antenna. After hearing my marina neighbor saying that I occasionally disappear from his AIS screen 10-15 minutes at a time and suggesting a dedicated antenna, I installed a $50 AIS antenna on the stern rail. The difference was rather dramatic. Now I am seen more consistently, and I see way more boats on my AIS screen than I used to. So it does appear that a dedicated AIS antenna gives more efficient in transmitting/receiving AIS signal.
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Old 22-08-2016, 15:55   #27
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Re: AIS Antenna

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Originally Posted by dannyjoh View Post
I initially set up a vesper marine transceiver and an antenna splitter for the mast-top VHF antenna. After hearing my marina neighbor saying that I occasionally disappear from his AIS screen 10-15 minutes at a time and suggesting a dedicated antenna, I installed a $50 AIS antenna on the stern rail. The difference was rather dramatic. Now I am seen more consistently, and I see way more boats on my AIS screen than I used to. So it does appear that a dedicated AIS antenna gives more efficient in transmitting/receiving AIS signal.
Well, to me that suggests that your masthead antenna installation is faulty in some manner, not that the AIS antenna is inherently better.

We have antennae on both masthead and solar arch, both normal VHF tuning. The higher antenna does far better at picking up distant ships.

Jim
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Old 22-08-2016, 16:31   #28
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Re: AIS Antenna

We have a receiving unit on a plain antenna and it works great.

Maybe there is some difference if one has a transmitter.

Cheers,
b.
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Old 22-08-2016, 17:27   #29
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AIS Antenna

Just have a receive unit - Digital Yacht AIS with wifi- and regularly get 30 to 40 NM with my masthead VHF antenna. When I was in Indian Key in southwest Florida, I was receiving ships near the Dry Tortugas showing ranges around 155 NM.

When my mast was down coming and going on the Tenn-Tom and Tennessee River to Mobile from Kentucky Lake, I mounted a Shakespeare AIS antenna on a 10 foot piece of PVC pipe u bolted to my stanchion. Both antenna setups go through a splitter. That put the antenna base 14 to 15 feet above the water. I typically picked up targets at around 8 miles when unobstructed by trees or terrain. I could not get good transmitting or receive on my regular VHF using this setup. I had to use my handheld into locks, communicating with tows and going into Marinas. My alternate antenna wire went into the same mast lead that my masthead antenna uses, so my assumption was that the AIS antenna wasn't good for normal VHF. I used a crimp connector, not soldered, so I suspect my installation was poor. Next time, I'll set it up in advance with an electronics installerI wonder if the AIS antenna wasn"t part of the problem. Does anybody use an AIS antenna tons it on VHF too?

I don't have an AIS transmitter, so have no experience with that side of AIS.


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Old 22-08-2016, 19:01   #30
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Re: AIS Antenna

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Originally Posted by dannyjoh View Post
I initially set up a vesper marine transceiver and an antenna splitter for the mast-top VHF antenna. After hearing my marina neighbor saying that I occasionally disappear from his AIS screen 10-15 minutes at a time and suggesting a dedicated antenna, I installed a $50 AIS antenna on the stern rail. The difference was rather dramatic. Now I am seen more consistently, and I see way more boats on my AIS screen than I used to. So it does appear that a dedicated AIS antenna gives more efficient in transmitting/receiving AIS signal.
YES! That's exactly what happened to my set.
Now I bypass the active Splitter just like you did.
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