Transponder/ADS-B

I'm trying to plan the location for my transponder (Dynon) antenna and the ADS-B antenna (Free Flight). I don't yet have the documentation for these products, but I understand that the distance between them should be about 5'. To do that, I'd like to put the transponder antenna near the battery (...3' away from the comm antenna which is on the belly below the rear seat) and the ADS-B antenna at the bottom rear of the tailcone (about a foot forward of the tie down ring). Problem is, my VOR antenna is right there. Is there a minimum distance to keep the VOR/glide slope antenna and the ADS-B antenna apart?

If I assume correctly that your Freeflight antenna is a receive only antenna, then proximity to another receive only (VOR/GS) should not be a problem at all.

The problems develop when you have two transmit antennas close together and especially if they are in the same frequency band... for example: transponder and ADS-B transmitter/receiver.

In this instance two things might happen: 1) The power transmitted by a transponder might overwhelm the bandpass filter of the ADS-B receiver or
2) the much more likely issue is that the receiving antenna re-radiates the energy of the transmitting antenna nearby. If they happen to be near 1/4 wavelength or multiple away then you wind up with a null in the antenna pattern.

TMI I suppose, but in summary, your installation should not be a problem.

Don

I have my transponder antenna under the pilot's seat, com antenna under rear seat, with no interference issues. Pilot seat location gives you more spacing for the adsb antenna, and a shorter cable run to the panel.

dhmoose said:

I don't yet have the documentation for these products

Click to expand...

I'd send an email to Dynon and Free Flight and ask them for a copy of their install/product manual so you can verify their recommended locations and separation needs.

Thanks all!

Much appreciated.

Make sure the aft antenna clears any reasonable orientation of the tail tie down rope.

BobTurner said:

Make sure the aft antenna clears any reasonable orientation of the tail tie down rope.

Click to expand...

Great point. I will do so!

ADSB Xpdr

There is about a 3 foot separation between my transponder antennas and it works fine. Both are on the belly aft of the baggage bulkhead. I have a GDL-39 and GTX-23. Love the traffic on it.

Transponder Antenna vs. ADS-B antenna...

I see this thread is a few years old, but I hope somebody reads my question..

I have in my hand a Commant transponder antenna and it is a very small blade (which is great).. I was told by someone who I respect that the ADS-B antenna is the same as the transponder antenna.. (which is also great) Just keep them at least 2' apart.... I think I can easily get 4' apart...

So my question is: "Do I buy another transponder antenna for the ADS-B and how far apart?"

By the way.. I really don't know what ADS-B is, but I am sure I will be using it!!

These are the recommendations from one UAT/ADS-B supplier.

The antennas should be well removed from any projections, the engine(s) and
propeller(s). It should also be well removed from landing gear doors, access
doors or others openings which will break the ground plane for the antenna.
? The antenna should be mounted on the bottom or top surface of the aircraft and in a vertical position when the aircraft is in level flight.
? Avoid mounting the antenna within 3 feet of the ADF sense antenna or any
COMM antenna, and 6 feet from transponder, DME and UAT transmit antennas.
? Where practical, plan the antenna location to keep the cable lengths as short as possible and avoid sharp bends in the cable to minimize VSWR.

Antennas:
The Comant CI-101 and RA Miller AV-22 stick-and-ball antennas and the Comant CI-105 blade antenna are examples that meet the requirements.

I had the same problem. Could only get about 3 feet distance between the transponder and ADS-B. Spoke with the company they were purchased from and said that 3 feet should be just fine.

Not flying so cannot confirm it is ok, but if not, I will move the ADS-B to the bottom of the wing.

I previously installed my transponder antenna under the RV 8 baggage floor on the left side. I mounted my Navworx ADSB antenna next to the innermost inspection cover on the right wing. This gave me the suggested 5 foot distance between the two and minimized cable length.

Works like a charm.

Don