The OH radical is an important player in known ozone depletion cycles; however, due to its location in the atmosphere, it must be studied from either a balloon or spaceborne platform. For long-term mapping over large portions of the Earth, a spaceborne platform is the most desirable. NASA's Earth Observing System Microwave Limb Sounder instrument is to house a 2.5 THz Schottky-diode receiver for such measurements. The authors describe the design, fabrication, and testing of the engineering model receiver front end. This is the precursor to the first terahertz heterodyne receiver to be flown in space