The 21-80-04-1 is a low pass filter designed to pass frequencies in the range 30-600 MHz and provide isolation to frequencies in the range 960-1220 MHz. The 21-80-04-1 comprises a Tchebyscheff low pass filter produced using discrete coils and low-loss chip capacitors, located on a thin printed circuit card within a aluminium alloy tubular housing, the ends of which are sealed and fitted with the RF connectors.