The TECOM Ft Belvoir Meteorological Team and the Night Vision and Electronic Sensor Directorate of CECOM contracted with EOIR to develop a new instrument which would provide atmospheric transmissivity data in the 35 gigahertz region. The desired instrument would have complete redundancy, long path length, compact size, stable microwave performance, easy field setup and alignment, standard data output, low development risk, and, above all, low system cost. The design by EOIR consists of mostly off-the-shelf components with a design goal of measuring 1% transmission over a 5 km path which corresponds to a rainfall rate of over 64 millimeters per hour. To achieve simplicity of design and field use and to keep cost down, two innovations have been made. First, a new antenna design that uses optical refraction principles replaces the large and cumbersome parabolic antennas and second, an open loop frequency design, as opposed to a frequency tracking receiver, allows for the use of less expensive transmitters and receivers. In this paper we describe the instrument and present some initial performance data.