AIS antenna near to radar reflector.

[BlueSkyNick]

Will it work OK?

The radar reflector is on the front of the mast. If I fit a standard VHF antenna on the side of the mast (just above a spreader) it will be protected from the genoa when tacking.

I believe the reflector to be tuned to radar frequencies in GHz, so shouldnt interfere with 150Mhz VHF reception for AIS. But if I then buy a transceiver, will my AIS transmissions become distorted, ie corrupted?

 

[boatmike]

You won't get interference from a radar reflector but it and the mast will block a signal in direct line with it if mounted at the same height. It would be a far better plan to mount it on the aft pushpit. You are not interested to get AIS signals from over the horizon so height does not matter. A short pole to put it above head height is good to avoid it getting knocked but not essential.

 

[kirielad]

Hi Nick

Just a thought, but can you fit your AIS aerial above the radar reflector?

It's very difficult to be sure how the radar reflector could affect reception of the VHF AIS signal. It may be that it increases the response on one tack, but acts as a shield on the other?

We had a similar problem on one of our workboats recently when installing a dedicated AIS aerial. It proved very difficult to find any 'clear' space away from stainless uprights or the radar reflector which was just slightly below, and we wondered if it would affect reception quality. Also it was only 500 mm from the main VHF aerial which again if you check all the books is not good news as you are supposed to have a good metre of horizontal clearance between aerials. However, it all works fine - I would certainly have been told all about it if not!

Perhaps in your case, if its possible to mount the new aerial above the radar relector (which would presumably then be on a different level to your existing VHF aerial), this would get round it?

 

[BlueSkyNick]

[ QUOTE ]
You won't get interference from a radar reflector but it and the mast will block a signal in direct line with it if mounted at the same height. It would be a far better plan to mount it on the aft pushpit. You are not interested to get AIS signals from over the horizon so height does not matter. A short pole to put it above head height is good to avoid it getting knocked but not essential.

[/ QUOTE ]

I've had an antenna mounted on a pole for the past couple of years, but it's rubbish reception - targets at 7 miles if lucky. Changed the Nasa engine from a Mk 1 to Mk 2 following advice on here - made no difference. I deduced that the feeder cable is knackered because the copper is blackened and it has a couple of joins in it. It was previously used for a Satphone connection from 1996. To replace it means removing furniture in the aft cabin which is a definite no-no.

Hence the new one up the mast.

If I can find a new way of mounting the GPS and Navtex antennae then the pole can go.

 

[RAI]

I tried my NASA AIS radar out first with the rubber antenna from my hand-held radio. It worked fine out to about 10 nm. I then mounted a pushpit mast and antenna with a new low-loss coax cable. Since I had to get a new/second radio for RAINWAT ATIS, I then got a splitter so as not to need a third antenna.

You could use a splitter to share your VHF antenna with the AIS. You only miss the AIS transmissions when you are transmitting voice. Mine is an "easySPLIT 2G".

 

[Anonymous]

You say 'AIS transmissions'? Are you installing a Class B AIS to transmit your own vessel's information (voluntary) or are you installing a receiver only? If the latter, then it won't transmit in any case.

You mustn't have the antenna too close to the mast in either case or the signal will be reduced considerably. Most people fit them on the pushpit or can be on the masthead with a plate or bracket spacing it away from the VHF radio antenna.

Another possibility, if you are receive-only, is to split the feed to the main VHF antenna, you can buy splitters for the job. People argue that the extra components reduce reliability which must be true, on the other hand, the antennae themselves are not very reliable compared with connectors and directional couplers so the reduction in reliability might be trivial. In any case, I imagine that you have an emergency antenna, so in extremis you would just connect that? If I wanted to fit an AIS receiver, that's what I'd do to save all the extra wiring, clutter, etc.

 

[boatmike]

Moody Nick. There is no need to fit the antenna high. Mine sits 11ft above the WL and reception is fine. Just fit a decent cable.

 

[BlueSkyNick]

Well in the words of a well known song - I did it my way.

Antenna now on side of mast help about 8 inches off by bracket. Seeing targets in all directions, up to 30 miles away from the marina, even with IoW in the way.

I know ships that distance away are totally irrelevent to me, but it's good to know I am getting a strong reliable signal from those who are at lot closer.

Job done.