Similar to the CI 109, the CI 121 is smaller in diameter and lighter at only 0.5 pounds. Features a tapered glass laminate housing and die-cast aluminum base. Offers standard mounting and appearance to many Cessna communication antennas. The CI 121 has been re-tested and upgraded to the new RTCA DO-160D environmental requirements and offers the 118 to 137 MHz frequency associated with DO-186A MOPS.