A cost-effective solution to measurement of hull-generated intermodulation interference on US Navy ships

Hull-generated intermodulation interference (IMI) signals occur when two or more RF induced currents flow in metallic junctions having nonlinear conduction characteristics. After a brief review of the problem, the approach taken to develop a cost-effective measurement system for IMI on US Navy ships, is described. An automated IMI assessment system approach was developed to allow IMI assessment testing to occur in an accurate, timely, and efficient manner. The configuration of the automated system for intermodulation assessment (ASIA) and the interface to the shipboard transmit system are described. The system consists of three major sections: VLF/HF receiver; the radio signal distribution unit (RSDU); and microprocessor/interface unit. The half-rack IEEE-488 bus-controlled receiver performs signal detection of the interference frequencies