Flipping stupid AIS aerial - what am I doing wrong?

Rivers & creeks

Rivers & creeks

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I read peeps on the forum saying how they get ships from 100 miles away with a rubber RIB aerial on the pushpit. Me, I'm not having any luck. If I plug in the masthead aerial I can get them from half way to the moon but any other aerial and all I get the boat 30 meters away and that's it. Is it all in the plug? I'm crap at wiring VHF plugs. How high does an AIS aerial need to be? Mine is 6 feet above the wheelhouse. Last year we had a mizzen mast and had a hawk on top of that and it got awesome AIS reception and transmission but that mast is long gone.

Advice? Tips? Ideas?

Thanks!
 
I had the same problem using a whip aerial on the tansom. I gave up in the end and fitted a Glomex splitter to the masthead aerial.
 
I had a pushpit antenna like you, and had the same problem. So I fitted a splitter to the masthead VHF and problem solved.

I now use the pushpit antenna as an emergency VHF antenna. Interestingly, when used for VHF, the range is very adequate - certainly works at 80nm when I tested it. However, it is woeful for AIS. I presume then that AIS receiver requires a higher quality signal than VHF and that there are various filters in the receiver to ensure that no partially corrupt data is used.
 
Thanks - I should have said it's a transponder so a splitter won't work :(

But great to hear I'm not the only one - do I have to put the mizzen mast back on :o
 
Colvic Watson said:
I read peeps on the forum saying how they get ships from 100 miles away with a rubber RIB aerial on the pushpit. Me, I'm not having any luck. If I plug in the masthead aerial I can get them from half way to the moon but any other aerial and all I get the boat 30 meters away and that's it. Is it all in the plug? I'm crap at wiring VHF plugs. How high does an AIS aerial need to be? Mine is 6 feet above the wheelhouse. Last year we had a mizzen mast and had a hawk on top of that and it got awesome AIS reception and transmission but that mast is long gone.
Click to expand...
What make of AIS do you have?

When I took delivery of my new to me boat I was a tad confused as all I was receiving was boats within 5 miles so had a look at the wiring. Turned out that the VHF wire from the AIS to the splitter had been left unplugged! So with 0.5m of coax I was pretty impressed. Once properly wired it was to the moon.

A splitter is the way to go.
 
My whip aerial is on a short mast on the pushpit & transmits/receives OK. However , when i bought the setup i was told that the whip aerial was slightly different to a VHF aerial. Not sure if this is B...x or not but it works really well & picks up from well over 15 miles.
Sold to me by Mainsprite & i do not put them in the "con" catagory so there may be something in the type of aerial used.
 
A couple of issues to consider:

Range is directly related to height above sea level. Your range in n.miles is 1.4 x root of the height above sea level (in Ft) of your antenna, total range is your range plus the range of whoever you're communicating with. If that's a big ship with an antenna a hundred feet up, range will be much better than when communicating with another vessel that has its antenna at deck level.

Also, not all VHF antennas cover the full marine band. most rubber duckies and some VHF antennas only cover 156 Mhz to 160 Mhz, or sometimes 162 MHz. for AIS you need an antenna that covers 156 to 163 MHz. On some antennas, not a rubber one, you can try lopping 2" off the whip and this could move the tuning point up to the AIS frequencies, but you'll lose out at the other end of the frequency range.

If you have a deck, or rail, mounted antenna be sure it isn't located near big lumps of metal and can "see" the horizon. an extension pole is a good idea if there is a lot of clutter lower down.

No reason not to use a good quality active splitter except you won't have a back up antenna.
 
Have my antenna on the pushpit arch. Reception is perfectly adequate there, i'm not interested in other vessels 100nm away. There is nothing to say it has to be at the top of a 50ft mast, how do mobos manage ?
 
My AIS works through a rubber stubby on the rear pulpit, and seems fine for my purposes. It's difficult to get a precise idea of range, because there are so many hills around Scotland to bounce signals off that "line of sight" doesn't really apply[1], but roughly speaking it seems to be good for 10 - 12 miles. OP, I'd check your connections and try using the AIS antenna for a radio check with your VHF set.

[1] The year before last I got a very clear AIS "sighting" of the MV Finlaggan while sailing on Loch Fyne. She was approaching Kennacraig on West Loch Tarbert ...
 
Salty John said:
Also, not all VHF antennas cover the full marine band. most rubber duckies and some VHF antennas only cover 156 Mhz to 160 Mhz, or sometimes 162 MHz. for AIS you need an antenna that covers 156 to 163 MHz..

.
Click to expand...

AIS uses channels 87 and 88 in the Marine Band (161.9 and 162Mhz). Any old aerial will do to receive, its just transmitting that needs a tuned aerial, so that it doesn't reflect back to the transmitter.
 
As per Salty John's post

Plus ... if you're in a marina, you''re surrounded by lots of big metal things sticking up all over the place and, most likely, in a hole in the ground. With an antenna mounted low down your AIS reception is likely to be fairly pants. Once you get out into open water, it should be perfectly adequate

You can run a transceiver through a splitter but it needs to be an active splitter which is considerably more expensive than a passive splitter (an active splitter switches the antenna between two transmitters thus avoiding the receive side of the inactive transceiver from being blasted to hell and gone by the active transceiver)

A final thought ... I'm beginning to seriously wonder if there isn't a downside to having an AIS transceiver antenna mounted high up. Obviously, given my line of work, I play around with quite a lot of kit on quite a lot of boats and I have a growing suspicion that the downside of masthead AIS antennas is reduced frequency of transmission especially when there's a lot of targets being picked up

My theory, and it's very much speculation at this stage, is that given that there are a limited number of transmission time slots available, a transceiver which is seeing targets at long range (> 10 to 15 miles, and mine merrily picks up shipping at 30 to 50 miles consistently and sometimes out beyond 100 miles if the conditions are right) sometimes struggles to find a "free" time slot whereas with a lower mounted antenna with reduced range the transceiver sees more "free" time slots

I'm not sure at this stage whether it's a significant issue (my feeling is that it isn't) but at some point in busy waters I'm going to switch around between my mizzen mast AIS antenna and (when I get the thing fitted) my pushpit rail mounted backup rubber duck and see what happens
 
Sorry, yes there are splitters that work with transponders. I have the range set to 6nm on the Matsutec AIS plotter as that's all I'm interested in but can't pick them up at that range unless I use the masthead. I'll try a standard hawk vhf aerial next.
 
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