Using an in-line uninterruptable power supply as TEMPEST ‘filter’ for naval vessels

A major objective of TEMPEST engineering is to separate equipment carrying classified (=RED) data from equipment carrying unclassified (=BLACK) data, to prevent unintentional radio or electrical signals, containing classified data, emission. RED/BLACK separation in the power supply system is in general achieved by adding TEMPEST filters, but on board naval vessels the power system is insulated and the use of filter capacitances is limited. Solid-state uninterruptable power supplies (UPS) create isolation, because of the AC/DC and DC/AC conversion and associated internal filtering. Measurements have been performed on an operational UPS to determine the a-symmetrical, symmetrical and non-symmetrical isolation. The results obtained from the UPS tested show very good isolation which, combined with the already installed power line filters inside equipment, will be more than adequate to achieve the required isolation for RED/BLACK separation.