AIS Splitter

[aknight]

I currently have a NASA AIS "Radar" unit installed on board Arabella. This unit does not output NMEA, being intended to operate as a stand-alone instument.

I am gradually assembling everything necessary to enable me to use my laptop as a chartplotter. I would like to be able to input AIS data so that it displays onscreen. I am prepared to purchase a separate AIS receiver, such as NASA's AIS Engine, but would like to leave the existing "Radar" unit installed for use as a back-up or when the laptop is not in use.

The existing "Radar" unit has its own dedicated VHF antenna, a Metz supplied c/o forumite Salty John. I'd like to use the same antenna as a feed for the new AIS Engine (or equivalent) that will be used with the laptop. Could the panel advise:

(a) whether there is any reason why I cannot use a splitter to get a VHF feed to both AIS units from the same antenna?

(b) whether there is any need to invest in a costly, dedicated AIS splitter (given that both units are receive-only, and no VHF Radio is connected to this antenna), or whether a cheaper alternative is available/advisable?

Thanks for any guidance you can offer.

Andrew

(edited for typo)

 

[VicMallows]

All you need is a very simple 2-way VHF splitter as used to be common for TV reception. You could even make your own up with (if I remember correctly) 3 resistors. The purpose of the splitter is so that each receiver continues to 'see' the correct impedance. It will introduce a signal loss of aprox 3dB. An alternative would be an active splitter/amplifier, but you would need to find a 12v one.

Personally at VHF frequencies I would first try just paralleling the two and see if reception was still satisfactory.

Vic

 

[aknight]

Thanks Vic. Just to check, you're referring to one like this from Maplin?

Andrew

 

[VicMallows]

Yes, That's precicely what I meant by a passive splitter.

Vic

 

[Blue5]

I fitted the NASA engine for the same reason to get AIS on the laptop, seem to remember reading that a separate aerial was preferable so located one on the stern rail at deck level, it works a treat and was easy to route and fit.

 

[jorgen]

depending on the other connectors, I would look for something a bit more robust. Maybe with F-connectors. The domestic TV splitter tend to get loose after some time, giving you a loss of signal strength.

 

[hubert]

I use the nasa radar and nasa engine on a single antenna with excellent results. I just use a BNC "T" adaptor from maplins and a couple of BNC to BNC cables.
http://www.maplin.co.uk/Module.aspx?ModuleNo=1582&criteria=bnc%20adaptor&doy=28m2
The nasa units have BNC connections so it makes sense to use BNC throughout.

 

[Salty John]

It's preferable in my opinion to use separate antennas for VHF and AIS. However, Andrew's problem is different: He wants to split the signal from his AIS antenna to two AIS receivers, which he can do with a simple passive splitter because he will not transmitting on this antenna.

 

[chuzzlewit]

Use a separate aerial-cheaper-safer-fewer connections-backup if mast comes down.

 

[Salty John]

See my post above. The problem here is splitting the signal from one antenna over two AIS's, not dividing the signal between a radio and an AIS receiver in which case two antenna's are the preferred choice.

 

[aknight]

Thanks to everyone for their help - what a fantastic resource this forum is! I'll go for the T-splitter from Maplins. It'll be the cheapest part I've bought for the boat in years...