Transponder antenna placement for Garmin GTX-45R

[outnumbered]

Trying to decide between these two options for transponder antenna placement. Any thoughts/feedback?

In tunnel right behind firewall
Pro's - Short coax length to GTX-45R (which is behind the panel)
- center of fuselage
Con's - Close to exhaust (not sure of this really would be an issue)
- any issue being right up against the firewall (i.e. wouldn't be able to support fuselage from below in that area if needed for maintenance)

In rear next to battery tray
Pro's - open area and easy install
Con's - longer coax run
- not centered with fuselage

​

​

 

[echozulu]

It depends on where your transponder is. I mounted my 45R behind the baggage bulkhead, so my antenna is one frame behind the baggage bulkhead. Works well.

 

[outnumbered]

It depends on where your transponder is. I mounted my 45R behind the baggage bulkhead, so my antenna is one frame behind the baggage bulkhead. Works well.

My 45r is behind the panel. So shortest cable route is in the tunnel by the firewall

 

[DRMA]

I have mine in the tunnel, between the front seats. It works well there on my RV-10. I selected that location as it is back from the exhausts, and not in alignment with the main gear legs which could theoretically shadow the signal. My 45R is just behind my panel.

Regards,

 

[bonefishdave]

I originally installed my antenna up near the firewall on my RV7 to keep the run short, however I noticed I was getting fluctuations in fuel flow caused by the energy output of the transponder. Moved the antenna behind the baggage compartment and the fuel flow was stable.
Using the red cube mounted to the engine mount.

 

[Avanza]

A minimum of three feet coax is required between antenna and GTX.

Good luck

 

[RyanWhite]

In my 9 I put it just aft of firewall way on right side. In the 10 I’m mounting both transponder and antennna in the back. I think I’m gonna need weight back there.

 

[Walt]

Ground plane should be approx 8” diameter.

 

[Carl Froehlich]

I put the XPDR antenna under the copilot seat, avoiding fuel and brake lines (sorry, no photo).
I put the ADS-b antenna and receiver aft near the battery.
The comm antennas are both in the tunnel. The forward one on the left side and the aft one on the right. This provides good clearance to the elevator push tubes.

I did this same placement on the first RV-10 build and everything works well.
Carl