Abstract: A secured scramble decoder filter comprised of a narrow band filter assembled on a fragile substrate and mounted in a housing wich automatically destroys the filter when any tampering is attempted. The filter is a series tuned network bridging a conductor coupled through a capacitor to a parallel tuned network, which is connected to ground. The coils for the filter are printed on a special electronic glass tube for temperature stability while the capacitors are deposited on the fragile substrate. The filter is mounted in a sealed housing in brackets with a spring, loaded to break the substrate when the device is tampered with to render it inoperative. The device is provided with a mounting screw requiring a special tool for removal so that when the device is mounted any prying in an attempt to remove the device will trigger the destruction of the filter.