Afc disabling system operative by reducing the d.c. discriminator output to zero

Claim 1

AN ANGULAR MODULATION RECEIVER HAVING AT LEAST: (A) ONE FREQUENCY TRANSLATING STAGE FOR THE RECEIVED SIGNALS INCLUDING A LOCAL OSCILLATOR AT A NOMINAL OPERATING FREQUENCY AND A MIXER TO PRODUCE THE FREQUENCY TRANSLATION OF THE RECEIVED SIGNAL; (B) AN AUTOMATIC FREQUENCY CONTROL CIRCUIT FOR SAID LOCAL OSCILLATOR INCLUDING A FREQUENCY DISCRIMINATOR FOR PRODUCING A DIRECT CURRENT OUTPUT SIGNAL WHICH IS PROPORTIONAL TO THE DEPARTURE OF SAID TRANSLATED SIGNAL FROM A PREDETERMINED FREQUENCY AND FREQUENCY CONTROLLING MEANS TO CONTROL THE LOCAL OSCILLATOR FREQUENCY IN RESPONSE TO SAID DIRECT CURRENT SIGNAL; (C) MEANS RESPONSIVE TO THE DIRECT CURRENT OUTPUT SIGNAL FROM SAID DISCRIMINATOR FOR DISABLING SAID AUTOMATIC FREQUENCY CONTROL CIRCUIT WHENEVER THE SAID DISCRIMINATOR OUTPUT SIGNAL EXCEEDS A PREDETERMINED VALUE TO RETURN THE LOCAL OSCILLATOR FREQUENCY TO ITS NOMINAL VALUE INCLUDING MEANS TO REDUCE THE DISCRIMINATOR OUTPUT SIGNAL IMPRESSED ON THE OSCILLATOR FREQUENCY CONTROLLING MEANS TO ZERO THEREBY TO RETURN THE LOCAL OSCILLATOR FREQUENCY TO ITS NOMINAL VALUE.