Dual G5 + GNC355 GPS signal source

[Martin S.]

Evening gents,

can somebody tell me where the GNC355 is getting the GPS signal from in this setup. The G5 is the only device directly connected to a GPS antenna. Also,
the RS232 connection between the GNC355 and the G5 is one-way, from the GNC to the G5. Im my understanding, the GNC can therefore only get the GPS signal through the ARINC 429. Is that correct? The manuals seems to be silent in that regard.

Many thanks for your help,

 

Martin

 

Martin

Edited October 28, 2023 by Martin S.

[EricJ]

The GNC355 is also connected to the ARINC bus from the GAD29B, which connects to the G5 via the CANBUS, so they can share some info, like the bug settings from the G5. 

I think the GNC355 is supposed to have its own GPS antenna, though.    

[PeteMc]

That's the diagram for the G5 installation.  Go look at the GNC355s installation diagram and you'll probably see a GPS Antenna.

 

[EricJ]

46 minutes ago, PeteMc said:

That's the diagram for the G5 installation.  Go look at the GNC355s installation diagram and you'll probably see a GPS Antenna.

 

And a vhf comm antenna.

[jamesm]

I believe that Garmin uses  RS232 steam which contains GPS position. I some GPS formats  you can connect your  laptop RX  and  ground  and using PUTTY application like and watch GPS position spit out.   True ARINC429 has 32 bits and uses 8 bits for label for the position among many other labels.  I have Dual G5's (which speak CAN and RS232 Serial) and GNC255 Nav/Com (speaks several variations of  Nav signals, serial RS232,and I think A429), GNC355 ( speaks  serial RS232 ,and A429), GNX375 ( speaks  serial RS232 ,and A429, gray code) and as others have said the GAD29B converts A429 to CAN. So the G5 can understand ARINC429 signals. I suspect  that's why Garmin isn't using the ARINC429 label field for position.

[PT20J]

The GNC 355 has a WAAS GPS receiver and VHF com transceiver. It must be connected to a GPS antenna and a VHF com antenna.

[PeteMc]

4 hours ago, EricJ said:

And a vhf comm antenna.

Yea... but let's not confuse the issue.  He just asked about the GPS! 

 

[Martin S.]

3 hours ago, PT20J said:

The GNC 355 has a WAAS GPS receiver and VHF com transceiver. It must be connected to a GPS antenna and a VHF com antenna.

Ok thanks for the info.

Let me be more specific. I've a dual G5 + GFC 500 (NO GPS navigator installed). My G5 ADI is fed by a GA 35 WAAS antenna. Let's say I wanted to add a GNC 355 to my setup. Can I unplug the GA 35 from the G5 ADI, connect it to the GNC 355, and have the GNC 355 forward GPS data (via RS-232 - MapMX) to the G5s, or will the G5s still need their "own" GPS antenna, e.g. a glare shield one?

According to the G5 installation manual (see below) it should be possible without, can somebody (with a similar installation) confirm?

 

Greets,

 

Martin

 

 

[PeteMc]

4 hours ago, Martin S. said:

Can I unplug the GA 35 from the G5 ADI, connect it to the GNC 355

Yes on the antenna move.  The GA35 is listed in the GNC355 Installation Manual as one of the approved antennae. 

But it is interesting that the 1.6.1.4 GPS Aiding document you posted does NOT list the GNC355.  Is it an older document?  I would think the GNC355 would work as I believe the "GPS" is the same in all three of the smaller boxes, but you might want to check with Garmin as to why it is not listed as a GPS Source for the G5.  (Hopefully someone else here will know the answer.)

 

Edited October 29, 2023 by PeteMc

[EricJ]

Most G5 installations with a separate GPS do not have an external GPS antenna connected to the G5.    The G5 just needs a GPS source from somewhere for alignment and correction, so the GNC355 can do that job.   If the GNC355 fails the G5 has an internal antenna that it can use if it needs to, or you can still connect an external antenna on the glareshield or wherever.    I've confirmed on mine that it works fine with only its internal antenna, so if I need to turn everything else in the panel off for some reason it'll still work.

 

[jamesm]

If I am not mistaken the internal G5 GPS uses a not WAAS antenna  (if connected)?  I believe it’s not required ).   I used the antennas specified by Garmin at the  time of my installation.

G5 non WAAS Antenna  /com combo antenna GNC355 WAAS/com antenna.

All new RG 400 coax cable was installed at the time of installation. As far as I know have had any antenna issues.

[PT20J]

Garmin makes a lot of equipment that can be installed in a myriad of configurations. The only way to understand all the requirements for a particular configuration is to refer to all the installation manuals. Be careful for things that are called out in one manual, but negated in another. For example, in a G3X installation, the G3X installation manual calls for removing the GTX 345 and GTN audio connections called out in the installation manuals for that equipment. Many an installer has read the GTN manual first and installed a connection and then realized after reading the G3X manual that they needed to remove it. 

[Martin S.]

Gents - thanks again for all the answers!