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So, how many GPS antenna?

F

Freemasm

Well Known Member
Sounds dumb but hear me out.

1@ 650xi GPS
1@ G5
2@ G3X

The need for the 650 antenna is not in question. With the others having the capability for their own antennas (antennae?), all being connected via CAN, some having BU RS232 links, where do you stop?

G3Expert?

Anyone?
 
One for the 650 (needs to be TSO anyway for IFR).
One for both G3X (I assume this is similar to how the Dynon SkyView works but I never installed a G3X).
Feed the G5 via the 650.
Feed the ELT via a 650 or G3X serial.
I assume your ADS-B out is via a serial from the 650, or perhaps the G3X network.

Result, two independent GPS sources. More is overkill.
 
I believe Garmin will recommend one for the G5 since it's supposed to be our primary back-up, I did, cheap insurance.
 
I chose to install a GA-26X for each of the two GDU's and one for the G5, all mounted on the glareshield.

There is also a GA-24 mounted on the glareshield for XM reception (4 glareshield antennas in total).

The GTN-650Xi uses the external TSO'd GA-35, which is the only topside external antenna.
 
I have 2 antennas mounted on the top behind the baggage compartment: one for the 650 and the other serves both G3xs and XM. The G5 internal antenna has been flawless, so I have not seen the need for an external antenna.
 
You can install one for the G5 and one each of your GDUs.

My G5 uses the GA26C on the glare shield. The unit needs a GPS reference to keep attitude info accurate.

The 650xi needs a Garmin GA 34, GA 35 or GA 36 unless you want Comant. Otherwise you have to find and check the relevant TSOs. TNC. TSO C144. I think that is a WAAS spec.

GDU’S use GA 55 or GA 56. BNC. TSO C129 CLASS A-1. There is a discrepancy in the G3X install manual. In edition AU, it is stated not to use GA3X WAAS antennas with G3X GDUs; but, in Section 20, the same manual states it is fine to do so and also provides some other antenna options. I used the GA 56 in my install.

After you think about it, I think the only question is do you want a GPS antenna on each of your GDUs or just one of them. One way to determine your comfort level is to wheel your build outside and see what happens when you start failing units.

One more thing is not to forget to create loss in your signal. I think the GTN xi and the GDUs both need some loss in the signal which you can create by having sufficient cable length. I used RG 400 and cut 8 foot lengths for each antenna connection.

Warm regards,
 
Drum said:
... snip ...

My G5 uses the GA26C on the glare shield. The unit needs a GPS reference to keep attitude info accurate.

... snip ...

Warm regards,
Click to expand...

My two G5s has worked great to keep attitude info accurate without an external GPS antenna for over 7-years.

The GPS antenna for the G5 is an option and may not be needed for your installation. It is NOT needed for my in the panel installation.
 
Carl Froehlich said:
One for the 650 (needs to be TSO anyway for IFR).
One for both G3X (I assume this is similar to how the Dynon SkyView works but I never installed a G3X).
Feed the G5 via the 650.
Feed the ELT via a 650 or G3X serial.
I assume your ADS-B out is via a serial from the 650, or perhaps the G3X network.

Result, two independent GPS sources. More is overkill.
Click to expand...
Yup. This reply is correct.
 
Drum said:
There is a discrepancy in the G3X install manual. In edition AU, it is stated not to use GA3X WAAS antennas with G3X GDUs; but, in Section 20, the same manual states it is fine to do so
Click to expand...
I'm not sure that's correct... the note in section 6.5 and the guidance in section 20 seem consistent to me.
 
Dad's RV-10 said:
I chose to install a GA-26X for each of the two GDU's and one for the G5, all mounted on the glareshield.

There is also a GA-24 mounted on the glareshield for XM reception (4 glareshield antennas in total).

The GTN-650Xi uses the external TSO'd GA-35, which is the only topside external antenna.
Click to expand...
I did the same. Plus a WAAS antenna on the top just behind the rear window for the Garmin 20A. So, four GPS antennas.

 
While you're fine having individual antennas for each GDU in the G3X system, you only need one antenna as the GDU's share data via CANBUS. The G5 will also share that data, but I agree with the "cheap insurance" sentiment; if it's the backup instrument, it should have its own antenna.

I have two GA35 antennas, one each for my G5 and GNX 375, and then a GA56 for the G3X, connected to my PFD. Everything is lit up with data.
 
Last edited:
I have a total of 3- one GA35 on the fuselage just aft of the canopy feeds the GTN650 and two pucks on the glare shield, one for the G3X internal gps and one for the G5.
 
mburch said:
I'm not sure that's correct... the note in section 6.5 and the guidance in section 20 seem consistent to me.
Click to expand...
You are correct.

The notes on page 6-5 and repeating on page 20-1, say, “
NOTE
GA 35, GA 36 and GA 37 antennas cannot be used with GDU 37X/4XX units.”

Reading a little more carefully now, on page 20-2, Table 20-2 says GA 34, GA 35 & GA 36 can be used with G3X but only with the GPS unit designated GPS 20A - which would not include GDUs.

Sorry for the confusion.
 
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