Radio search and intercept system including serially connected frequency determining units with increasing passbands

Claim 1

IN A RECEIVING SYSTEM FOR MONITORING A WIDE FREQUENCY SPECTRUM AND DETERMINING THE FREQUENCY OF A RECEIVED SIGNAL IN SAID SPECTRUM, A FREQUENCY DETERMINING UNIT, COMPRISING: AN IF AMPLIFIER HAVING A PREDETERMINED PASSBAND; A FIRST FILTER HAVING A PASSBAND EQUAL TO THE UPPER HALF OF THE PASSBAND OF SAID AMPLIFIER; A SECOND FILTER HAVING A PASSBAND EQUAL TO THE LOWER HALF OF THE PASSBAND OF SAID AMPLIFIER; A FIRST RECTIFIER CONNECTED TO SAID FIRST FILTER AND DEVELOPING A DIRECT VOLTAGE WHEN A RECEIVED SIGNAL IS COUPLED THROUGH SAID FIRST FILTER; A SECOND RECTIFIER CONNECTED TO SAID SECOND FILTER AND DEVELOPING A DIRECT VOLTAGE WHEN A RECEIVED SIGNAL IS COUPLED THROUGH AND SECOND FILTER; IMPEDANCE MEANS CONNECTED TO SAID RECTIFIERS SO THAT CURRENT FLOW FROM ONE OPPOSES THE OTHER; AND SWITCH MEANS RESPONSIVE TO SAID CURRENT FLOW TO INDICATE THE FILTER COUPLING SAID RECEIVED SIGNAL.