Transponder and ADS-B Antenna Ground Plane Questio

Dynon101

I love flying!<br />
Joined
Mar 5, 2016
Messages
382
Can someone please provide some advice on what I should do with respect to mounting my transponder and ADS-B antennae?

I’ve read the forum post on the Jim Weir EAA article and the Skyview installation manual.

I have a flying Velocity that I am doing a complete rewire because I am installing a Dynon Skyview system. Since the airplane is already completed I cannot get too creative with installing antennas in the wings or wing tips and some of the installations so in some instances I am stuck with what I got.

The airplane has existing antennae mounted in the wings for VHF NAV and COM and it also has a single transponder monopole antenna mounted on the copilot side aft floorboard (under the rear seat). This antenna is mounted in a way that the antenna is mounted to the bottom of the airplane (sticking strait down) and the connector end of the antenna sticks up through the fuselage floor and it is mounted to the corner of an egg shaped ground plane (why they used egg shape instead of square/rectangle I do not know…perhaps a scrap piece of metal was laying around or is it due to not wanting to precisely cut out the ground plane in precisely the wrong shape). Attached is a PDF showing a picture.

I have installed a radio rack in the copilot side of the nose compartment directly on top of the canard. I need to try to avoid locating the antenna up front because on the pilot side of the nose compartment is the ADHRS units and they have the magnetometer.

The SV manual transponder section does not address anything about the ADSB antenna. The ADSB section does state to not install the antenna within 24 inches of the transponder antenna.

Should the monopole antenna be installed in the middle of the ground plane or on the edge/corner (no guidance from the manuals)?

Should the ground plane be grounded to the aircraft engine?

What are the intervals that the transponder ground plane should be?
120 MM X 120 MM is minimum
700 MM X 700 MM is too big for my airplane.
What are the intermediate steps that are best and what should be avoided?

What are the intervals that the ADSB ground plane should be?
130 MM X 130 MM is minimum
780 MM X 780 MM is too big for my airplane
What are the intermediate steps that are best and what should be avoided?

Any advice would be GREATLY APPRECIATED!!!
 

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dynonsupport

Dynon Technical Support
Staff member
Joined
Mar 23, 2005
Messages
13,226
The antenna goes in the middle of the ground plane. Your current ground plane is just extra weight, but it doesn't hurt. You need to make sure that the antenna is 60 mm or farther from the edge at the closest however.

There is no interval above 120 or 130mm. Any bigger is a bit better, but not by much. My plane has 120 and 130 mm squares.

The ground plane only needs to be grounded to the outer conductor on the coax.

The nose might be an excellent place for an ADS-B antenna. It doesn't transmit so it won't interfere, and we can calibrate out the slight magnetic effect it has.
 

timfwalsh01

Member
Joined
Jan 20, 2008
Messages
189
Location
Alexandria, VA
I just finished my ADSB install on my Velocity today!!

Antenna is located in the belly of the aircraft (between my header tank and the firewall).  I drilled a hole in the bottom and the antenna is sticking out.  Caution - the fuselage is too thick.  I have the antenna mounted on the ground plane sticking out the bottom.  Ground plane is mounted to the floor.

I have a complete Skyview system in my plane, happy to chat!!

timfwalsh01@comcast.net

Tim
 

skysailor

Active Member
Joined
Oct 17, 2008
Messages
596
I used the small ground plane that Dynon suggests. I made it from a small piece of scrap in the shop. Better yet, you can mount it internally. The Velocity is fiberglass. Mine is mounted internally in a Glasair and it performs flawlessly with no drag!
 

Dynon101

I love flying!<br />
Joined
Mar 5, 2016
Messages
382
Thanks all! Home Depot sells some 24 inch by 12 inch very thin aluminum sheets for just 10 bucks each. I will cut some to the dimensions indicated in the dynon manual and I will Mount them flat on the floorboard of the airplane and mount the monopole antenna bass directly to the groundplane and I will drill a hole in the floor board and stick the antenna down straight through. It looks like the realistic location would be in the back of the airplane under the rear seat. I will post pictures.

Tim are you on the VBOA forum?

Thanks again for all of your help and well wishes!
 
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