Transponder and ADSB Antennas

[Swingwing]

I am getting ready to install my antennas. To keep things simple and coax runs short, I really would like to install the RAMI ADSB and transponder blade antennas just aft the firewall inboard of the fuel vents on my RV-7.

(The two com antennas are on the belly 8" behind the spar)

Doing a search others have installed the ADSB and transponder antennas at the firewall. Has anyone had problems with the installation of these antennas at this location? Could the close proximity to the RV7 landing gear create an issue?

 

[Walt]

Suggest you follow the transponder IM recommendation as closely as possible if best performance is your goal.
From Garmin:
Transponder antenna considerations help the installer to select the best location for the antenna. The antenna should:
1. Be attached away from major protrusions, such as engines, nacelles, propellers, and antenna masts.
2. Be as far as practical from landing gear doors, access doors, or other openings that could affect its radiation
pattern.
3. Be vertically attached on the bottom of the aircraft.
4. Not be attached within three feet of the ADF sense antenna or any other communication antenna.
5. Not be attached within six feet of a DME antenna.
6. Be attached a minimum of three feet from the GTX 3X5 to prevent RF interference

 

[Carl Froehlich]

Yep - decisions to be made.

I mount the XPDR antenna under the co-pilot seat (RV-10) and I experienced no issue with the proximity of the landing gear. The Comm antennas are staggered aft of that (the second further aft of the first) with access via the tunnel. The ADS-B antenna and ADS-B receiver (Dynon) get mounted much further back, aft of the baggage compartment bulkhead. The receiver is mounted on a simple “Omega” shaped tray of 0.032” aluminum that is pro-sealed to the inside bottom of the fuselage. The tray has nutplates for the receiver. The antenna is in the same area, providing for a very short (low loss) coax run. The receiver is connected to the network with a single, four #22 conductor shielded wire. This is a data connection, not RF so no signal loss.

Carl

 

[Thermos]

I really would like to install the RAMI ADSB and transponder blade antennas just aft the firewall inboard of the fuel vents on my RV-7.

That's where mine is, and I've had no problems with ADS-B/transponder operation.

HTH

Dave

 

[rapid_ascent]

Nick,

Mine are mounted exactly as you suggest. One on each side. No performance info though since I'm still building. I used some of the antenna doublers that Vans sells for additional stiffening. I've included some pics of what I did. Use your own judgement for your install.

 

[bonefishdave]

For what it’s worth, I initially put mine next to the left fuel vent near the firewall. I was getting variations in fuel flow with the transponder on as the red cube was just on the other side of the firewall. Moved the antenna back behind the baggage area and fuel flow variations stopped.

 

[BillL]

Suggest you follow the transponder IM recommendation as closely as possible if best performance is your goal.
From Garmin:
Transponder antenna considerations help the installer to select the best location for the antenna. The antenna should:
1. Be attached away from major protrusions, such as engines, nacelles, propellers, and antenna masts.
2. Be as far as practical from landing gear doors, access doors, or other openings that could affect its radiation
pattern.
3. Be vertically attached on the bottom of the aircraft.
4. Not be attached within three feet of the ADF sense antenna or any other communication antenna.
5. Not be attached within six feet of a DME antenna.
6. Be attached a minimum of three feet from the GTX 3X5 to prevent RF interference

My -7 has the xpndr "post" at the firewall, but - to comply with Walts #4 on the list, the ADSB had to go behind the baggage compartment.

BTW - on antenna - - I placed my GPS antenna under the cowl. While all performance criteria were met, there was an unexpected problem. My WAAS antenna failed and emitted a signal that jammed the other GPS antenna within 3 feet (on an IFR flight plan). Recommend consideration of the aft turtle deck location for that antenna.

 

[Swingwing]

Thank you to all for sharing you knowledge and what you did. This is very helpful as I make the final decision on where to put the antennas. One option I didn’t previously consider is mounting the transponder and adsb units remotely and running wire instead of coax cable

 

[bjdecker]

For additional consideration - If you go with a Garmin GTX345 (or similar), you only need one antenna for Mode S / ADSB-Out / In functionality and compliance.