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transponder antenna location

NTex

Well Known Member
Does anyone have experience mounting their transponder antenna near the firewall near the co-pilot rudder pedals?

Found this example online:

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Would this location interfere with any future floorboards/carpet or with the passengers feet!?

I've got too many antennas, and the manuals seem to say that none of them play nice together so I have to figure a way to keep them separated.

Thanks
 
I have a 7A, and have my transponder antennae mounted in the upper right corner of the fuselage (just behind the firewall). I think I may have had to make split in the carpet for the cable, but other than that, it has worked well in this location for me for the 4 years that I have been flying.
 
Txp antenna

Just moved mine to that location for separation from the UAT antenna and comm antennas. About 2 inches inboard of the fuel vent, 2 inches behind the firewall. Working just fine there. Antenna coax is just in front of my carpet.
 
Same Location

Just moved mine to that location for separation from the UAT antenna and comm antennas. About 2 inches inboard of the fuel vent, 2 inches behind the firewall. Working just fine there. Antenna coax is just in front of my carpet.

I have mine the same, works great.
 
Transponder/UAT antennas require a ground plane to operate efficiently like other antennas, 8" diameter in the recommended minimum for xpdr/uat.
 
Thanks for all the quick replies!

I'll put it in this location and call one more thing done...

This is a delta pop transponder antenna, FYI.


Transponder/UAT antennas require a ground plane to operate efficiently like other antennas, 8" diameter in the recommended minimum for xpdr/uat.

Isn't the aircraft skin the ground plane? Or are you talking about the doubler size?
 
Isn't the aircraft skin the ground plane? e?

Yes it is - as long as it is a conductor. Walt's concern is that, going forward, do you have at least 4" of aluminum skin? Or do you transition onto the fiberglass (non conducting) cowling?
 
exhaust

You may want to give some consideration to your exhaust proximity with this location as well.
 
Yes it is - as long as it is a conductor. Walt's concern is that, going forward, do you have at least 4" of aluminum skin? Or do you transition onto the fiberglass (non conducting) cowling?


Ah, gotcha...

I'm ignorant with this stuff, so thanks everyone for chiming in with their experiences.

The avionics manuals are good, but the hard part for me is finding locations for all the remote components (LRU), antenna, and cable bundle wiring routing! I miss the sheet metal construction that tells you explicitly what to do (I'm a simple guy).

Anyway, sounds like I'll try to keep the antenna coax connection 4 inches aft of the firewall and 2 inches inboard of the fuel vent. This should give enough clearance from the exhaust, provide a good ground plane, and still clear the co-pilot rudder pedals.

Thanks again for the help!
 
In my -7A, I put the XPNDR and ADSB antenna under the MLG mount far enough aft that feet/heels would not be able to kick it. With the XPNDR mounted on the right side of the sub-panel and ADS-B in box on the left, the antenna cables are around 3 feet long and easily secured.
 
This link might help on the in explaining the ground plane size

I think all you need is about a 2.5" radius for the 1030-1090mhz transponder frequency range. so because you have a .5" lip in front of the FW you should be able to put the center of antenna back just 2 inches, so it's out of the way of any feet. the link below may help. also if you search antenna ground plane calculator, putting in the frequency will give you the ground plane size. Mine is just 2" from the FW and I fly long IFR flights up and down the east coast with no ATC issues....well not from the transponder anyway.

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1328697560/5
 
lips don't count

Conductors that are perpendicular to the ground PLANE (a flat surface) don't count. That said, this is more art than science, and with a very large ground plane running aft you may well get acceptable performance with a small ground plane running forward.
Note to previous poster about fuel vent 2" away: make sure the vent is a lot shorter than 7 cm (2.8") so it doesn't resonate with the transponder frequency.
 
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