Built a support bracket, identical too but opposite the Comm antenna support bracket. This will install on the oposite side of the fuselage from the comm antenna. A transponder antenna will be installed here and wired thru to the instrument panel, The ADS-B tansmitter will not be purchased untill the airplane has flown, but its easier to accomodate for it now. I hope I dont have the antenna too close to the step that sticks out of the fuselage. There may be some radio interference...well we will see.