Ship RFI survey procedure for HF frequencies: A task under the Shipboard EMC Improvement Program (SEMCIP)

The document provides a method of obtaining the most meaningful information possible regarding the potential RFI situation on a ship from data taken under severe time restrictions. Discussion is limited to the HF band, 2-30 MHz, but similar tests conducted at other frequencies will provide results of equal merit. Since the effect of RFI on reception capability, rather than the phenomena causing it, is being investigated, the ship's receiving subsystem is used to monitor RFI signals with a minimum of special equipment. The fundamental question is, How great is the potential for RFI due to intermodulation interference signals on this specific ship. It is chiefly asked (1) during sea trials of new construction, (2) prior to a scheduled shipyard availability for an operational ship, and (3) just after work in a shipyard has been completed. The method does not simulate operational conditions by activating a majority of the available transmitters simultaneously. By monitoring individual interference signal levels when only two transmitters are operating, it provides accurate predictions of the severity of operational interference conditions. If RFI potential is high, the most important source can be determined. If several sources are found, they are automatically ranked in order of importance.