ADS-B in (receive only) antenna does not require a ground plane of any size. A simple TED stick/ball transponder antenna on a bracket will do nicely. Just mount it low in the fuselage with the best possible downward conical exposure (not blocked by metal objects) for the best results.
For ADS-B out (transmit & receive), you will need a ground plane and the appropriate size antenna for the system (1090ES or UAT) you are using. A UAT system would use a slightly longer antenna and larger ground plane than the traditional 1090ES transponder type due to its slightly lower 978 frequency.
120mm square ground plane for transponders (1090ES)
130mm square ground plane for UAT systems and appropriate antenna
Put the antenna in the center, .020 aluminum is fine for this use, radius the corners ¼” or so
I’ve installed several…all work very well.
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of Richard Sessions
Sent: Sunday, June 21, 2020 10:40 PM
Subject: [Canard Zone] ADSB In - Classic Cozy 3 Antenna Placement Experience
I know there has been a lot of discussion on the ADSB-In antenna placements a few months back, but curious to see what people are getting good results with in
a Classic Cozy 3 now that there has been a little more time and likely more experience.
I know there was the slot antenna and others, but I am thinking a 13"ish square foil for the dipole under the left thigh support. I know it is a projection and subject to ridicule, but pretty simple and not a lot of changes / structure in the back seat area.
I am hooking up to a Dynon HDX system in a panel upgrade and it is about the last thing I have when my newly repaired ADAHRs gets back (static port failure....).
Feel free to contact me off line as I am sure most feel we have done this to death.
Richard Sessions, Cozy 3 N9455 (William Chorley builder if anyone has anything on it)
Houston's Ellington Field (KEFD) - Go RAFE!
rtsessions@..., 281-467-2432 (leave a message with all the spam....)