Originally Posted by Timberwolf
Garmin does a phenomenal job of putting out schematics for all things experimental....except transponder interfaces. I figured that one out the hard way installing a GTX 345 in with a G3X system and GTN650.
I'm now installing a GTX35R in my -6 with a G3X and GTN 625, but the have again noticed the literature is lacking. The schematics show only what to hookup for a 45R, but I can't find anywhere that it explains where the control for the unit comes from. I've deduced I'll need the following, if anyone can verify it would be greatly appreciated.
RS-232 connection to GSU25 (Encoder info)
RS-232 connection to GDU 4xx ( I assume that with it configurd to Connext 57600 Baud this is used to actually control the transponder, though it never says that anywhere...it just says ADSB traffic/weather which isn't applicable to the 35R)
Ethernet connection to GTN 625 (out 3A/3B) Provides GPS position
However I can assume no connection needed to GTN625 Ethernet IN 3A/3B.....or are these connected for TIS-A traffic?
Please look at pages 27-26 and 27-27 of the Rev. AF G3X Installation Manual. It shows you everything you need to know to wire a GTX 35R to your equipment.
As shown on these drawing you need 2 RS-232 connections:
1. RS-232 connection between GSU 25 and GTX 35R which provides altitude data and transponder control, and also provides TIS-A data to all the GDU 4XX displays in the system if you decide to use TIS-A (most do not since ADS-B traffic is so good).
2. RS-232 connection between GTN and GTX 35R to provide GPS position data to the GTX 35R.
As noted on page 27-26, the Ethernet connection to the GTN is only used on the GTX 345/345R/45R models that have a built-in ADS-B receiver. There is no Ethernet interface on the GTX 335/335R/35R transponders.
The single ARINC 429 transmitter on the GTX 35R is automatically configured to output TIS-A traffic when TIS-A traffic is enabled, but currently only the GNS series units will receive TIS-A traffic in this manner (not the GTN).
We are not aware of any way to send TIS-A traffic to the GTN from a GTX 35R. Since we recommend that TIS-A be disabled on the transponder when an ADS-B receiver is installed (to keep things simple), there is seldom a reason to enable TIS-A in these systems. As mentioned above, TIS-A traffic is available for display on all the GDU 37X/4XX displays if anyone wants to enable and use it.
All of the wiring guidance for a GTX 345/345R/45R with G3X and GTN is provided on a single page, 27-25.
Please let us know if you have additional questions.