Secure communication line

Claim 1

IN COMBINATION, AN INTRUSION DETECTION SYSTEM AND A SECURE TRANSMISSION LINE TAMPER PROTECTION SYSTEM COMPRISING ALARM RELAY MEANS RESPONSIVE TO THE OUTPUT OF SAID DETECTION SYSTEM, FIRST OSCILLATOR MEANS ENERGIZED THROUGH SAID ALARM RELAY MEANS WHEN SAID DETECTION SYSTEM IS NOT ALARMED, SECOND ENERGIZED OSCILLATOR MEANS MODULATED BY SAID FIRST OSCILLATOR MEANS, CONDUCTOR MEANS CONNECTED BETWEEN SAID SECOND OSCILLATOR MEANS AND A MONITOR FACILITY, DETECTOR MEANS ELECTRICALLY CONNECTED TO SAID CONDUCTOR MEANS IN SAID MONITOR FACILITY TO DEMODULATE THE MODULATED OUTPUT OF SAID SECOND OSCILLATOR MEANS ON SAID CONDUCTOR MEANS, FIRST INDICATOR MEANS CONNECTED TO SAID DETECTOR MEANS AND RESPONSIVE TO THE OUTPUT THEREOF LESS THAN A PREDETERMINED MAGNITUDE TO INDICATE DE-ENERGIZATION OF SAID SECOND OSCILLATOR MEANS AND SYSTEM FAILURE, DIFFERENTIATOR MEANS ELECTRICALLY CONNECTED TO SAID DETECTOR MEANS TO DIFFERENTIATE THE OUTPUT THEREOF, SECOND INDICATOR MEANS CONNECTED TO SAID DIFFERENTIATOR MEANS AND RESPONSIVE TO THE OUTPUT THEREOF IN EXCESS OF A PREDETERMINED MAGNITUDE TO INDICATE TAMPERING WITH SAID CONDUCTOR MEANS, AND THIRD INDICATOR MEANS CONNECTED TO SAID DETECTOR MEANS AND RESPONSIVE TO THE ABSENCE OF THE OUTPUT OF SAID FIRST OSCILLATOR MEANS IN THE DEMODULATION OUTPUT OF SAID DETECTOR MEANS TO INDICATE INOPERATIVENESS OF SAID FIRST OSCILLATOR MEANS AND INTRUSION OF THE PROTECTED AREA.