FA50 and GPS



We are about to install an upgraded Nav system including a MFDBB, DRSDOME, GP330B, and FA50.

The GP330B is going to be connected to the DRSDOME directly. The FA50 will be connected to the MFDBB using a NMEA2000 backbone.

The question is, with the GP330B already connected to the MFDBB, do we need to have the 'internal' antenna for the FA50 installed, or is there a way to set it up to use the GP330B data over the network as the 'external antenna'? (we'd like to avoid running another cable if will just be redundant).
Yes, the "internal" GPS (GPA017) antenna that comes with the FA50 must be attached to the FA50 in order for it to work. It's not mandatory that the GPA017 be installed so that it will actually get a fix, but it must be connected in order for the GP330B information to be used from the network. In other words, you can simply connect the GPA017 to the FA50 and stow the antenna down with the FA50 processor. The advantage of installing that antenna where it can get a fix is that the MFDBB will then have a backup source of GPS in case the GP330B stops working.
By the way, I re-read your post "The FA50 will be connected to the MFDBB using a NMEA2000 backbone."...

The FA50 is an Ethernet device, not NMEA2000. It has a NMEA0183 output capability which would work to the MFDBB, but would be a waste of time to wire it up that way. Bottom Line: The NAVnet 3D system doesn't support NMEA2000 AIS. Just wanted to make that clear.
Wondering that fa50 is working with no fix of ist own Antenna. From what I know AIS Transponders must use ther own dedicated gps source (and may share Position to other Units),

@chongl: If I were you I would install the gps Antenne for the fa50 where it can get a fix. Ok, ist some extra work but if gps Position is vital, it is always a good idea to have a backup. I once lost one gps antenna due to a stupid crewman and was very "happy" that I only had to Change the Position source.
The FA50 is setup like an IMO AIS which requires 2 GPS sources in case one is lost. The IMO AIS systems use the external GPS as the primary source and if that's lost uses the internal GPS (one that's plugged into it) as the backup. The FA50 only needs to sense that an internal GPS is present (i.e. the GPA017 that comes with it) before it'll go out and use the GPS from the NAVnet network. It's true that if the network GPS information is lost, the AIS will no longer function because the internal GPA017 cannot get a fix if stowed under a dash next to the FA50 processor. So, answering your original question about it being a requirement to install the GPA017 on the mast, the answer is no because this isn't an IMO AIS system, but it must be connected for the FA50 to use the GPS information from the network connection.

Having said that, it's always recommended to install the GPA017 antenna for the FA50 where it can get a fix because then it can also be used as a backup source for the NAVnet and the AIS will continue to receive GPS information from it's own antenna if the NAVnet source fails.