AIS Antenna Height

[haydude]

Does an AIS transponder setup require two aerials, one for transmission and one for reception?

Absolutely NOT

 

[BrianH]

For the past 8 years I've only had an AIS receiver with antenna mounted on my wind generator 2.5m mast. Now I have a Amec Camino-101 I shall use the same antenna for the combined transmit and receive function. My previous experience with that has given consistent reception of between 5-20nm for Class A and even Class B at that minimum distance.

I think height and resultant distance is a bit academic, after all, for seeing and being seen with AIS it all boils down to the nearest couple of miles of a potential collision area - anything else is clutter. All this talk of masthead antennas is relevant only for VHF radio contact. Mast-less powerboats manage well enough, when I look on MarineTraffic there are plenty of those showing up all over.

 

[GHA]

I think height and resultant distance is a bit academic, after all, for seeing and being seen with AIS it all boils down to the nearest couple of miles of a potential collision area - anything else is clutter.

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Not completely sure about that, the big boys do collision avoidance movements a lot before they even appear over the horizon, and they're the ones it would be nice to let know you're there. But I've no idea how much difference it would make to what their sets see if an antenna was kicking out a decent signal

 

[BrianH]

Not completely sure about that, the big boys do collision avoidance movements a lot before they even appear over the horizon, and they're the ones it would be nice to let know you're there. But I've no idea how much difference it would make to what their sets see if an antenna was kicking out a decent signal

With their relatively high antennas they surely can see a Class B target at 5nm, with a pushpit-mounted antenna or equivalent ... IF they have ECDIS monitoring. That should give them plenty of time to consider any course changes.

 

[Pinnacle]

That looks a really good arrangement. The antenna is vertical and held away from the stay.

Why thank you kind Sir!

 

[Pinnacle]

True. Perhaps he could have gimballed it.

If Ken would like to come round to the boat and update it to a gimballed version, he would be most welcome.

 

[GHA]

With their relatively high antennas they surely can see a Class B target at 5nm, with a pushpit-mounted antenna or equivalent ... IF they have ECDIS monitoring. That should give them plenty of time to consider any course changes.

Way offshore anyway, it's mostly all been done by 5Nm away, I've watched them do it (on AIS receive) and Vhf ed up to say thanks. That's was me being seen by radar, but the point stays, I think big boys do collision avoidance much further away than many sailors believe.

If height of transmitter on a little sailing boat makes much difference then getting seen by them I don't know, but suspect a good instalation with as little loss as poss and a decent antenna might have more effect.

 

[BrianH]

Way offshore anyway, it's mostly all been done by 5Nm away, I've watched them do it (on AIS receive) and Vhf ed up to say thanks. That's was me being seen by radar, but the point stays, I think big boys do collision avoidance much further away than many sailors believe.
If height of transmitter on a little sailing boat makes much difference then getting seen by them I don't know, but suspect a good instalation with as little loss as poss and a decent antenna might have more effect.

I'm sure you are right about efficient antenna matching. I was testing my transponder at home with a quarter-wave piece of wire stuck in the output socket and the monitored AIS serial output stream to the PC was warning that O/P power was down to 1.6W. That's not much but should be better with the proper installation when I get down to the boat.

 

[GHA]

I'm sure you are right about efficient antenna matching. I was testing my transponder at home with a quarter-wave piece of wire stuck in the output socket and the monitored AIS serial output stream to the PC was warning that O/P power was down to 1.6W. That's not much but should be better with the proper installation when I get down to the boat.

The hams are lucky with stuff like http://wsprnet.org/drupal/ to monitor how good the signals are.
As the frequencies are near enough the same would using a Vhf radio to do a DSC test call to a coast guard give you any hints as to how well signal is getting out?
Keep sailing away and see when you stop getting replies?

 

[Twister_Ken]

Doesn't all this fol-de-rol go to show that an active radar transponder is a better bet if you're concerned to be seen by traffic of sufficient size to wipe you out?

 

[BrianH]

The hams are lucky with stuff like http://wsprnet.org/drupal/ to monitor how good the signals are.
As the frequencies are near enough the same would using a Vhf radio to do a DSC test call to a coast guard give you any hints as to how well signal is getting out?
Keep sailing away and see when you stop getting replies?

I plan on giving my old receiver to a friend with whom I regularly sail in company with. We go cruising the northern Adriatic together and often are well separated; he will surely report on how well he has kept my position. This is indeed a problem - to install a transponder and have no idea how it is performing.

 

[Andy_H]

I am afraid i dont have any pics that clearly show how its done - I will try and remember to take a few when I am next on the boat.

So, here goes with a description;

Talking to a rigger at SIBS in 2011, he advised against using any sort of crimp or clamp onto the backstay stainless wire itself, as it is possible it could deform the wire and create a weak point. So instead, I have fixed it to the eye swage at the bottom of the fixed part of the backstay. To keep the aerial vertical, I made a small teak wedge that sits between the antenna bracket and the swage. The bracket and the wedge are fixed to the swage by bolts that pass through an eye strap similar to the one in this picture; http://www.ebay.co.uk/itm/2-X-4MM-WIRE-EYE-STRAPS-IN-STAINLESS-STEEL-316-/151123634605?pt=UK_CarsParts_Vehicles_BoatEquipment_Accessories_SM&hash=item232faba9ad#ht_2382wt_1388

Its not a great effort, but below is my attempt at a sketch to show the fixing position and method. Hope it helps.

View attachment 38850

Thats really helpful. Thanks very much

 

[BrianH]

Doesn't all this fol-de-rol go to show that an active radar transponder is a better bet if you're concerned to be seen by traffic of sufficient size to wipe you out?

Absolutely. The ideal is to have both. I appreciate having an AIS receiver and seeing myself what is out there and if it should be avoided without having to rely on anyone else's actions.

 

[GHA]

Doesn't all this fol-de-rol go to show that an active radar transponder is a better bet if you're concerned to be seen by traffic of sufficient size to wipe you out?

Probably, or a steel boat or both.

 

[Pinnacle]

Doesn't all this fol-de-rol go to show that an active radar transponder is a better bet if you're concerned to be seen by traffic of sufficient size to wipe you out?

Is this a ( pretty poor ) attempt to get out of gimballing my antenna?

 

[Pinnacle]

Doesn't all this fol-de-rol go to show that an active radar transponder is a better bet if you're concerned to be seen by traffic of sufficient size to wipe you out?

I view it more as an additional "good to have". A good one ( for example, Echomax Active-XS Dual Band Radar Target Enhancer ), has an RRP of c£800, incl masthead bracket, so not exactly what you would call cheap.

A radar enhancer will tell you you have been painted, but not the number, range, speed course, or position of the sources. Also, you are relying on the other party taking ( in fog for example ) the avoiding action. At least with AIS you can see on your plotter who the ones to worry about are and can make your own informed decisions.

So, in a perfect world I would have both.

 

[lw395]

Well, yes, but only vertical when the boat is not heeling or pitching or rolling.

That's true of all antennas to a greater or lesser degree.
It would be foolish to have a high gain VHF or AIS aerial, resulting in a limited vertical pattern.
Active radar repeaters often have quite low angles of heel to the first null.

 

[lw395]

I plan on giving my old receiver to a friend with whom I regularly sail in company with. We go cruising the northern Adriatic together and often are well separated; he will surely report on how well he has kept my position. This is indeed a problem - to install a transponder and have no idea how it is performing.

You can tell that the antenna and downlead are good because you receive other ships' signals.
The path loss from you to them should be the same, by reciprocity.
So the only unknown is your output power.

 

[Koeketiene]

Does an AIS transponder setup require two aerials, one for transmission and one for reception?

No - got VHF/AIS RX & TX/FM all on one masthead aerial (with splitter).

 

[prv]

A radar enhancer will tell you you have been painted, but not the number, range, speed course, or position of the sources. Also, you are relying on the other party taking ( in fog for example ) the avoiding action. At least with AIS you can see on your plotter who the ones to worry about are and can make your own informed decisions.

I don't think Ken's advocating RTE instead of AIS receive. On past showing, he and I are agreed that a RTE together with an AIS receiver are the best combination for shipping avoidance. If there's still money left over then AIS transmit adds some interesting extra benefits.

Pete