Using GPS antenna for AIS

[obmij]

Hi

I have a pushpit rail mounted GPS antenna which is no longer in use.

I am about to fit an AIS receiver which requires an external antenna.

Any reason why I can't connect the two? If so would I need any kind of adapter? The GPS antenna is the robust mushroom shaped kind and is not easily breakable, whereas I reckon the lifespan of a 'whip' VHF/AIS antenna mounted on the pushpit would be measured in minutes..on my boat anyway.

Alternatively, are there any recommended fittings to fit a whip antenna onto the backstay?

Going to do the work this weekend and hoping to have all required bits with me.

Cheers

 

[Martin_J]

Some of those GPS domes are just an antenna for a specific GPS unit.. Others are powered and return GPS information via an NMEA stream..

You would need to know what type of GPS dome you have (perhaps by describing the cable or what it was connected to) before we could say if it would work..

Do you happen to know what dome it is, what AIS unit you are planning on getting and what provision for VHF antenna you have.. Thanks in advance.
As for AIS reception - it is the VHF antenna that is needed to receive the AIS VHF signals. The GPS part is required in order to be able to plot target positions in relation to your own position.

 

[prv]

AIS works at 150ish MHz. GPS works at 1.5GHz. The antennas are not interchangeable, and in any case your GPS mushroom probably has a built-in amplifier that the AIS receiver won't supply power for.

So no, it won't work.

I wouldn't like to try fitting a whip antenna to a backstay either. If installed close together, the parallel metal will probably affect the reception, if installed further apart the movement of the stay will probably whip the antenna around all over the place.

Pete

 

[Martin_J]

Sorry - To summarise...

A combined AIS receiver/display (e.g. NASA AIS RADAR) will need to receive both VHF and GPS information.
An AIS engine will need the VHF input and will output NMEA to an external plotter (that has it's own GPS source).

 

[obmij]

Thanks Martin, Pete

Existing unused antenna is Garmin, looking at pictures on web it is a GA29 which I believe is 'dumb' It was originally connected to a GPS128

The AIS is Digital Yacht AIS100 pro, which will display on a Garmin 551 (which has it's own built in antenna, hence my spare on the pushpit)

So it wont even work in the way a coat-hanger shoved into the telly will pick up a signal?

 

[prv]

Existing unused antenna is Garmin, looking at pictures on web it is a GA29 which I believe is 'dumb' It was originally connected to a GPS128

Ok, that's the kind I was assuming. It's an antenna, not a receiver emitting NMEA, but it does contain an amplifier running off (I believe) 5v applied between the core and the screen by the Garmin 128.

Still no use as a VHF antenna.

So it wont even work in the way a coat-hanger shoved into the telly will pick up a signal?

If you plug it in and pick up anything at all, I would suspect the cable acting as an antenna rather than the GPS dome.

If you don't want a metre-long VHF antenna whipping about on the pushpit, why not get a rubber-duck about 8 inches long, like for a handheld? The ANT200 AIS I had on my last boat came with one of these, and it worked ok.

Pete

 

[Daydream believer]

I have a whip mounted indirectly on the push pit but I actually have it fitted to half a sailboard boom which is fitted to the pushpit with a couple of u bolts. the (extending) sail board boom then has the whip on the end of that. I can raise it a couple of feet if I want
I have an echomax active reflector on the other half of the boom on the opposite side of the boat
the boom is cut just after the main curve & the aluminium is good quality anodised
The bottom part is neoprene covered so there is no electrolysis between u bolts, pushpit & aluminium
There must be dozens of them in people's garages just doing nothing & would be a lot cheaper than stainless tube