AIS antenna location

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RobbieH

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I've just fitted a class B transponder. It seems to be working fine at short range. It picks up boats around it and transmits to (at least) the end of the pontoon, verified on amother boats receiver.

However I don't see the boat on any of the Internet tracking sites when several boats just down the pontoon are being picked up. I suppose that is because the antenna is past its sellby date and/or is mounted to low to reach an AIS relay station that is serving the Internet sites. The antenna is a standard vhf whip currently mounted on the pushpit. I'm thinking of renewing the antenna (it's quite old and perhaps the connections require remaking anyway).

Is there any reason not to locate on the radar arch? That would give me an extra meter of height ASL and should improve the radio horizon slightly. It would also get it out of the way - the antenna often gets in the way when faffing around the stern with mooring lines etc.

It would be in close proximity - about 30 cm distance to the radar scanner (Navico broadband). I can't think of an RF reason why this would be a problem, are there any other considerations?

Note I don't want to invest in a splitter to use the masthead antenna, I like having separate antennas with the option to reconnect the ais antenna onto the vhf (or vice versa) if one gets damaged.

Tks,

Robbie
 
I have a VHF antenna on the pushpit that works fine with receive only AIS, can't see as transmit would be any different. My last boat was a mobo and had conventional Radar, VHF and AIS antennas all on the roof (at similar heights) and everything worked fine.
 
Ah, but my mates boat can be seen. Most annoyin.

RF is unpredictable stuff (and I work for a company that produces RF planning tools!). I guess I should wait till we get out of the harbour and see if we manage to reach the shore stations then.
 
RobbieH said:
I've just fitted a class B transponder. It seems to be working fine at short range. It picks up boats around it and transmits to (at least) the end of the pontoon, verified on amother boats receiver.

However I don't see the boat on any of the Internet tracking sites when several boats just down the pontoon are being picked up. I suppose that is because the antenna is past its sellby date and/or is mounted to low to reach an AIS relay station that is serving the Internet sites. The antenna is a standard vhf whip currently mounted on the pushpit. I'm thinking of renewing the antenna (it's quite old and perhaps the connections require remaking anyway).

Is there any reason not to locate on the radar arch? That would give me an extra meter of height ASL and should improve the radio horizon slightly. It would also get it out of the way - the antenna often gets in the way when faffing around the stern with mooring lines etc.

It would be in close proximity - about 30 cm distance to the radar scanner (Navico broadband). I can't think of an RF reason why this would be a problem, are there any other considerations?

Note I don't want to invest in a splitter to use the masthead antenna, I like having separate antennas with the option to reconnect the ais antenna onto the vhf (or vice versa) if one gets damaged.

Tks,

Robbie
Click to expand...

I don't believe antenna height is your problem. I find that a 1.5m above water height easily gives you a 5 n-mile range and up to 8 for ships with hight aerials. Try another/borrowed aerial if you think your one is faulty before changing its location.

Www.solocoastalsailing.co.uk
 
RobbieH said:
I've just fitted a class B transponder. It seems to be working fine at short range. It picks up boats around it and transmits to (at least) the end of the pontoon, verified on amother boats receiver.

However I don't see the boat on any of the Internet tracking sites when several boats just down the pontoon are being picked up. I suppose that is because the antenna is past its sellby date and/or is mounted to low to reach an AIS relay station that is serving the Internet sites. The antenna is a standard vhf whip currently mounted on the pushpit. I'm thinking of renewing the antenna (it's quite old and perhaps the connections require remaking anyway).

Is there any reason not to locate on the radar arch? That would give me an extra meter of height ASL and should improve the radio horizon slightly. It would also get it out of the way - the antenna often gets in the way when faffing around the stern with mooring lines etc.

It would be in close proximity - about 30 cm distance to the radar scanner (Navico broadband). I can't think of an RF reason why this would be a problem, are there any other considerations?

Note I don't want to invest in a splitter to use the masthead antenna, I like having separate antennas with the option to reconnect the ais antenna onto the vhf (or vice versa) if one gets damaged.

Tks,

Robbie
Click to expand...
You must install it above the radar beam. I have a pole for the the radar with the AIS antenna sitting over the radar dome.
 
RobbieH said:
I guess I should wait till we get out of the harbour and see if we manage to reach the shore stations then.
Click to expand...

Sounds best. Or even go out and get a mate with a receiver to go out at the same time and sail 5 or 6 miles apart.
 
knuterikt said:
You must install it above the radar beam. I have a pole for the the radar with the AIS antenna sitting over the radar dome.
Click to expand...
Photo
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as knuterikt says, dont put it in line with the radar scan, that could be bad.
Also a general VHF aerial is a compromise, you will most likely get better performance from an aerial tuned for the AIS band.
Range, the higher you are, the greater the range (yeah,I know you know) but at 1.7m above sea it will see 2.5nM and another boat the other side will make that up to 5nM. Mebby a bit short in high seas.
By far the most significant thing you say is that it gets in your way: move it for sure.
 
RobbieH said:
The antenna is a standard vhf whip currently mounted on the pushpit. I'm thinking of renewing the antenna (it's quite old and perhaps the connections require remaking anyway).
Click to expand...

Think this is the solution to your problem but mounting it higher will help too and stop someone grabbing it to keep their balance.

Pete
 
We had the same issue, fitted the transponder a few months ago and could only see others and could never get seen on the internet, went out of the creek last week and as soon as in the shipping channel got picked up on marine traffic in minutes. Receive has never seem to be an issue even low down on berth wend tides out but don't forget cat A ships are putting more power out.

We have small AIS stubby on the pushpit.
 
Daverw said:
We had the same issue, fitted the transponder a few months ago and could only see others and could never get seen on the internet, went out of the creek last week and as soon as in the shipping channel got picked up on marine traffic in minutes. Receive has never seem to be an issue even low down on berth wend tides out but don't forget cat A ships are putting more power out.

We have small AIS stubby on the pushpit.
Click to expand...

Were other Class B targets with a SOG of zero shown when you weren't? Maybe the website just filters them out.
 
Coverage by land based ais stations is full of gaps for type B transponders. For example Tees bay is not covered despite having a lot of shipping and ferries. I often do trips without appearing on boat watch, marine traffic etc . The system still is worth its weight in gold as it shows shipping movements around the vessel. Suggest you hail other leisure sailors under way and see if they can see you before moving your aerial .
 
I know that the AIS aerial has to be a minimum of 3m above the waterline for the Fastnet race this year. It's a new requirement but I'm unsure if it's a RORC prescription, ISAF or what. We're going down an antenna splitter route for this so we can use our masthead aerial. My experience with the transponder and the existing 2m height aerial is a maximum range between 5-10 miles.
 
Hi I have had the same problem in Fleetwood marina I do see class A Boats nearby on Marine traffic until I went out into the bay when it showed up, to try to improve the range I made a Ariel jump lead so that I can swap the AIS to the mast head Ariel rather than the one up my wind geny pole I don't think it makes much difference but at least other ships can see me when out at sea, I have checked this with friends when both at sea. My concern was that I had bought a much cheaper than most so perhaps not very good, it is a Matsutec 102.
Mi,e
 
If you have any doubts at all about the aerial and its cable/connectors I would certainly replace it. My choice would be a Metz AIS optimised aerial from Salty John as mentioned by another poster. Excellent quality aerial from a reliable, knowledgeable supplier, no connection other than satisfied customer. It's length is chosen for optimum AIS use but more than adequate for use at all marine VHF frequencies for emergency use. Yes, height is an important factor but if the aerial is poor (especially on transmit) you are at a loss (pun intended!) right from the start. The cost of a new aerial is small I imagine compared to the total cost of your electronics on board and is the vital item in the chain. Most problems I come across are down to faulty aerials or horribly made up RF connectors, especially those "easy fit" twist on PL259's. Rant over !
The total system can only be as good as its aerial.
Good luck. Richard
 
As said I would think from the symptoms that you have a bad antenna. Try connecting the main VHF com antenna for comparison. Location on pushpit should be oK. An antenna is just a bit of wire so it is the connections to it that cause all the trouble. If it is a 17 inch wire rod then check the centre of the coax to the rod for continuity and the outer of the coax to the metal the antenna is attached to. If it is a 1.5m fibreglass tube with gubins inside then cut around the base and open it up you may find corrosion and or bad joints. This latter may justify a new antenna. Try searching home made VHF antenna. olewill
 
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