Digital time domain mode ranging system

Claim 1

A DIGITAL RANGE SYSTEM COMPRISING: PULSE GENERATING MEANS; DIVIDING MEANS FOR DIVIDING THE OUTPUT PULSE REPETITION FREQUENCY OF SAID PULSE GENERATING MEANS INTO A FIRST PULSE REPETITION FREQUENCY FOR OPERATION IN A FIRST MODE AND A SECOND PULSE REPETITION FREQUENCY FOR OPERATION IN A SECOND MODE; TRANSMISSION MEANS FOR SELECTIVELY TRANSMITTING SAID FIRST AND SECOND PULSE REPETITION FREQUENCIES; RECEPTION MEANS FOR RECEIVING THE RETURN SIGNAL OF THE PULSE REPETITION FREQUENCY BEING TRANSMITTED AS A REPLY PULSE; MEANS FOR GENERATING A RANGE GATE PULSE; SAID RECEPTION MEANS RECEIVING SAID RANGE GATE PULSE TO PRODUCE A RANGE SIGNAL WHEN SAID RANGE GATE PULSE AND SAID REPLY PULSE ARE SIMULTANEOUSLY PRESENT IN SAID RECEPTION MEANS; SWITCHING MEANS RESPONSIVE TO A PLURALITY OF SAID RANGE SIGNALS TO SWITCH SAID DIVIDING MEANS FROM SAID FIRST MODE TO SAID SECOND MODE AFTER A SELECTED NUMBER OF SAID REPLY PULSES HAS BEEN RECEIVED IN SAID RECEPTION MEANS; ERROR DETECTOR MEANS FOR RECEIVING SAID RANGE SIGNAL AND GENERATING AN ERROR SIGNAL IN RESPONSE TO SAID RANGE SIGNAL; AND FIRST SWEEP MENS FOR DELAYING THE GENERATION OF SAID RANGE GATE PULSE IN RESPONSE TO SAID ERROR SIGNAL; SECOND SWEEP MEANS FOR ACTIVATING SAID FIRST SWEEP MEANS THROUGH SAID SWITCHING MEANS SO THAT SAID FIRST SWEEP MEANS VARYINGLY DELAYS THE GENERATION OF SAID RANGE GATE PULSE; THE OUTPUT OF SAID SECOND SWEEP MEANS BEING A LINEARLY VARYING, REPETITIVE SIGNAL; MEANS FOR COUNTING THE NUMBER OF PULSES IN SAID OUTPUT PULSE REPETITION FREQUENCY; SAID COUNTER MEANS BEING DEACTIVATED WHEN SAID RANGE SIGNAL IS PRESENT SO THAT THE NUMBER OF PULSES COUNTED IN SAID OUTPUT PULSE REPETITION FREQUENCY IS INDICATIVE OF THE DISTANCE TRAVELED BY SAID REPLY PULSE.