Will the Comant DME/Transponder CI-105 work with the Becker mode C transponder?
Yes the CI-105 is a standard transponder antenna and can be used for both mode C & S transponders.
Is the connector on the antenna a female BNC connector?
Yes, it is a female BNC. You will need to order a male BNC based on what type of coax cable you use (either RG 142 or RG 58).
What is the minimum recommended separation distance between the two aerials.
Typically 3 feet is a good distance between antennas.
Do you need a ground plate for this Comant CI-105 antenna? Which size?
Yes all antennas need a ground plate. Normally the height of the antenna should be the diameter of the ground plate but larger is better.
Will this antenna work with a Trig TT22, and do I need to make a ground plane or can I buy one? Is all the mounting hardware included?
Yes, this antenna is compatible with all aviation transponders. The ground plane can be as simple as foil tape part number 11-12900. Hardware not included, only gasket.
I am installing a Garmin GDL-88D with diversity, meaning it uses 2 antennas, one on the bottom of the fuselage and one on the top. Is this Comant CI-105 antenna approved and suitable for use on the top of the fuselage?
No. This antenna is meant for use on the bottom of the fuselage only.