VHF splitters and GPS antennae

[whiteoaks7]

One of the points that came out of my post about ONWA Class B AIS transponder is a discussion on splitters. So here's all I know about them followed by a question: Splitters divide the signal in two (usually) so 3dB or half the power is lost to each of the output arms. This means half the power received by the antenna is available to whatever device you hang on the end - VHF radio, AIS engine etc. This may or may not be a problem depending on the strength of the incoming signal you start with and the sensitivity of your devices.

Now the question: The ONWA transponder needs an external GPS antenna and so I'm considering using the Garmin antenna that feeds my GPS152 (yes it's old but we love it). My worry is that the antenna may be active i.e. is fed power from the Garmin to a head amplifier or something. If so then putting a splitter in that line may cause all sorts of issues with another device that is also trying to power an antenna. So: in general are GPS antennae active?

 

[duncan99210]

Splitters tend to be designed for a set frequency, so you'll need a gps signal splitter to make it work. The ones I've spotted aren't cheap, coming in at $300+ see here https://www.gpssource.com/collections/gps-splitter . And that's before determining if the signal output by the Garmin antenna would be compatible will your AIS.

 

[RichardS]

One of the points that came out of my post about ONWA Class B AIS transponder is a discussion on splitters. So here's all I know about them followed by a question: Splitters divide the signal in two (usually) so 3dB or half the power is lost to each of the output arms. This means half the power received by the antenna is available to whatever device you hang on the end - VHF radio, AIS engine etc. This may or may not be a problem depending on the strength of the incoming signal you start with and the sensitivity of your devices.

Now the question: The ONWA transponder needs an external GPS antenna and so I'm considering using the Garmin antenna that feeds my GPS152 (yes it's old but we love it). My worry is that the antenna may be active i.e. is fed power from the Garmin to a head amplifier or something. If so then putting a splitter in that line may cause all sorts of issues with another device that is also trying to power an antenna. So: in general are GPS antennae active?

Doesn't the transponder come with it's own antenna? I thought that they had to.

I can't see why an antenna with a booster would interfere with a GPS signal splitter (not something I've ever heard of or used) but I would try the supplied antenna below decks if there is one.

Richard

 

[Hoolie]

The external antenna used by the Garmin GPS 152 has an in-built low noise amplifier powered by the display head. I can't see how you could pass this connection through a splitter. The GPS 152H has an integral antenna, but has a completely different mounting. Don't ask how I know

 

[lw395]

You can get splitters that will do GPS, but it seems to be cheaper to buy another aerial.
Probably nice to have the redundancy too.

 

[dk]

The rules state that an AIS GPS antenna must be separate to any other. You cannot just take the GPS data from a network and feed it into your AIS transponder, or vice-versa.
The antenna splitter divides the use of the VHF antenna between your VHF radio and the AIS transponder. A transponder requires an active splitter. I don't see what this has to do with the GPS, which connects into a different socket altogether.

 

[RichardS]

The rules state that an AIS GPS antenna must be separate to any other. You cannot just take the GPS data from a network and feed it into your AIS transponder, or vice-versa.
The antenna splitter divides the use of the VHF antenna between your VHF radio and the AIS transponder. A transponder requires an active splitter. I don't see what this has to do with the GPS, which connects into a different socket altogether.

I made the same mistake above but have now edited my post.

The OP is talking about putting a passive coax Y-splitter in the coax output from his GPS antenna so he can share a GPS antenna between two devices. As I said, I've never heard of such a thing or ever used one but they are presumably available.

AIS transponders will not allow a shared GPS signal through their NMEA inputs but I don't see how the transponder could detect a shared GPS signal into its coax input.

Richard

 

[lpdsn]

Glancing around the websites, the UK distributor includes a GPS antenna with the transponder. The ONYA website says it's included as an option - the English is obviously non-native so hard to see exactly what they're saying, but you could check.

 

[MikeCC]

Just use a separate GPS antenna to avoid any sort of compromised system. As said before, AIS transponders are required to have independent GPS source.