I am using a Microair transponder and blind encoder unit. I bought the transponder/encoder unit as a kit which included the antenna, the wiring harness and the coaxial cable etc.
I mounted the encoder on the firewall (inside surface). Thanks to the wiring harness the hook-up was fairly simple. I did install and wire a circuit-breaker specifically for the transponder as I did for all the avionics (VHF, Transponder and GPS).
