AIS antenna conundrum

[Cardo]

We have an AIS transponder that currently uses its own dedicated antenna that's atop a pole mounted on the stern. The pole was originally a home for the radome, however the radome now lives up the mast, so the pole's only use is to house the AIS antenna (we also fly our ensign off it!).

We're having a passarelle fitted to make our Mediterranean experience more comfortable. Unfortunately, the pole, which sits close to the centre of the stern, will foul the halyard for the passarelle. So we're trying to decide how to get around this.

The options we've thought of so far are:

1) Remove pole and mount AIS antenna elsewhere. The antenna is a standard steel whip, I don't know where else would be suitable for this. We could get a different antenna (a stub?) and mount this on the pushpit. Would that be acceptable for a transponder?

2) Move pole to the corner, out of the way. Drawbacks are making new holes for this and the antenna would be an eyesore in a new place!

3) Have the AIS share the antenna with the VHF. I'd rather have independent antennas for redundancy, but if an affordable box of tricks could do it, then that could work.

4) ?? Any ideas?

Unfortunately, the pole itself is not sturdy enough to take the passarelle halyard. That would have been neat!

 

[nigelmercier]

We could get a different antenna (a stub?) and mount this on the pushpit...

A stubby on the pushpit is where I intend to mount mine, the range will be more than adequate. Also gives the ideal location to swap leads for an emergency VHF antenna.

I'll keep quiet about my thoughts on splitters for now, or people will think I'm a fanatic

 

[bromleybysea]

+1 never really understood why people go for splitters. KISS. One more thing to go wrong, no spare VHF antenna.

 

[Twister_Ken]

i have a stubby on the pushpit (RX only) picks up traffic at an approx range of 10 miles.

 

[Salty John]

Move the pole to the corner. A standard 1m vhf whip on a pole is the best arrangement for a deck level transmitting antenna because it gets the antenna above the superstructure and you benefit from its broad radiation pattern.

 

[nigelmercier]

i have a stubby on the pushpit (RX only) picks up traffic at an approx range of 10 miles.

Which is ideal, and with a transponder it reduces clutter for others.

 

[Martin_J]

I had the same conundrum this last winter - and like others did not at the time like the idea of a splitter.

Unfortunately ISAF regulations had other ideas in 2014...

3.29.1 The following shall be provided:
n) An AIS transponder
p) An AIS antenna shall be mounted on top of the main mast.

So - after looking into the specifications of splitters from Vespermarine, Raymarine, Digital Yacht, Em-trak, Comar, AMEC, Sevenstar, Easyplit and True Heading.. I did buy and fit one a few months back.

The advantage now is that I have moved the AIS unit from the back of the boat to a position near the chart table and led the original pushpit mount antenna cable to the chart table as well. Very easy to reconnect to the pushpit antenna to VHF if needed but I don't expect to have to because the splitter is fail safe (i.e. Tx/RX path direct between VHF and antenna).

My worries about the splitter seem to have gone and the AIS Tx is stronger after making use of the much more expensive (and less lossy) masthead antenna feed cable.

 

[Martin_J]

.. and you might smile... but the one disadvantage was a surprise...

With the chart plotter now receiving AIS information from over 75 miles away... I'm sure the vast number of 'ais targets' on the screen has slowed the plotter refresh rate down

 

[RAI]

.. and you might smile... but the one disadvantage was a surprise...

With the chart plotter now receiving AIS information from over 75 miles away... I'm sure the vast number of 'ais targets' on the screen has slowed the plotter refresh rate down

My plotter has an option to set the maximum radius of interest in AIS targets displayed. But I've never noticed it slowing down because of them.

 

[Martin_J]

The SH plotter seems to display all targets up to a limit of 200 and I seem to think I was at about 190 targets at the time...

I did not see any way of reducing the number of targets displayed

There is a setting for reducing the 'Active Target' radius but that only reduces the no. of targets that show distance/turn information although reducing this may help.

(Apologies for thread drift).

 

[RAI]

(Apologies for thread drift).

Not really, I have a VHF antenna on top of the main mast and another push-pit pole plus an AIS splitter for one of the two VHF radios. An old NASA AIS "radar" has a stub antenna too. The newer Class B transponder is back on the splitter and one VHF on the push-pit pole antenna. I've been trying to find an antenna problem, as I'm not getting the range I used to get when the Class B was first installed.