Digital tracker

Claim 2

In a range-tracking system of the type wherein interrogation pulses are transmitted from a first station to a remote second station and in response to each interrogation pulse a reply pulse of a first predetermined duration is transmitted from said second station and received at said first station, the actual range between said stations being proportional to the time delay between the transmission of an interrogation pulse and the receipt of a reply pulse in response thereto, said system including first means for generating a range gate pulse of a second predetermined duration at a time delay with respect to each transmitted interrogation pulse corresponding to a predicted range between said stations, and second means responsive to the order of occurrence of a reply pulse with respect to the occurrence of a range gate pulse following the transmission of each interrogation pulse for changing said predicted range in a direction which tends to reduce the error between said predicted range and said actual range, the improvement therein: wherein said first means generates a range gate pulse having a second predetermined duration which is substantially equal to said first predetermined duration of a reply pulse, and wherein said scond means comprises a range analog gate for passing only the portion of each reply pulse which overlaps a range gate pulse in occurrence, and further means responsive to the time of occurrence of the passed portion of each reply pulse with respect to the then-existing value of the predicted range between said stations for making said change in said predicted range.

Claim 3

A system according to claim 1 wherein said further first means includes detector means responsive to each reply pulse portion passing said range analog gate for determining the centroid of said reply pulse portion and means responsive to said detector means for determining the actual range to said second station and making said change in said predicted range.

Claim 4

A system according to claim 2 wherein said means responsive to said detector means includes means for limiting changes in the determination of the predicted range, whereby the possibility of tracking false reply pulses is minimized.

Claim 5

A digital tRacker for tracking reply pulses from an acquired and verified remote station remotely located relative to an interrogation station carrying said digital tracker, said interrogation station being of the type incorporating means for transmitting interrogation pulses at a predetermined repetition rate, said reply station being of the type incorporating means responsive to said interrogation pulses for transmitting reply pulses having a predetermined duration, said interrogation station further having means to acquire and verify the presence of said remote station in response to said interrogation and reply pulses thereby to provide a first control signal and a second control signal corresponding respectively to each of said interrogation pulses and to each of said reply pulses from said acquired and verified remote station, comprising, a. normally inoperative range gated analog means for receiving and passing said reply signals, b. detector means coupled to said analog means for converting said reply pulses to digital pulses, c. means responsive to said digital pulses and said first control signals for counting the time interval therebetween and generating a third control signal representing said time interval, d. means responsive to said third control signal for determining the range to said remote station, e. said counting means including means responsive to said first and second control signals to initially generate a fourth control signal for enabling said analog means, said fourth control signal having a duration substantially equal to the duration of said reply pulses, whereby reply pulses from an acquired and verified remote station preset said counting means with a first time interval manifesting a first range to said remote station, f. said counting means including means reponsive to said digital pulses and said first control signals to subsequently generate said fourth control signal to enable said analog means to thereby track said remote station after being acquired and verified by passing at least a portion of said reply pulses to said detector means.

Claim 6

A digital tRacker for tracking reply pulses from an acquired and verified remote station remotely located relative to an interrogation station carrying said digital tracker, said interrogation station being of the type incorporating means for transmitting interrogation pulses at a predetermined repetition rate, said reply station being of the type incorporating means responsive to said interrogation pulses for transmitting reply pulses having a predetermined duration, said interrogation station further having means to acquire and verify the presence of said remote station in response to said interrogation and reply pulses thereby to provide a first control signal and a second control signal corresponding respectively to each of said interrogation pulses and to each of said reply pulses from said acquired and verified remote station, comprising, a. normally inoperative range gated analog means for receiving and passing said reply signals, b. detector means coupled to said analog means for converting said reply pulses to digital pulses, c. means responsive to said digital pulses and said first control signals for counting the time interval therebetween and generating a third control signal representing said time interval, d. means responsive to said third control signal for determining the range to said remote station, e. said counting means including means responsive to said first and second control signals to initially generate a fourth control signal for enabling said analog means, said fourth control signal having a duration substantially equal to the duration of said reply pulses, whereby reply pulses from an acquired and verified remote station preset said counting means with a first time interval manifesting a first range to said remote station, f. said counting means including means reponsive to said digital pulses and said first control signals to subsequently generate said fourth control signal to enable said analog means to thereby track said remote station after being acquired and verified by passing at least a portion of said reply pulses to said detector means.

Claim 7

A digital tracker according to claim 4 further including means responsive to said counting means for determining the range rate of said remote station.

Claim 8

A digital tracker according to claim 5 further including means responsive to said range and said range rate determining means for determining the time for impact with said remote station.

Claim 9

A digital tracker according to claim 4 wherein said detector means generates a digital pulse whose leading edge is substantially coincident with the centroid of said reply pulse, said detector including an analog delay line having a plurality of taps, and means for summing and comparing two equal groups of said taps to determine the centroid of said reply pulse.

Claim 10

A digital tracker according to claim 7 including means responsive to the output of said analog delay line for generating said digital pulse having its leading edge corresponding to said centroid.

Claim 11

A digital tracker according to claim 5 including a register for storing the time count from a previous count, means for comparing said time count to the registered time count, means for altering the count of said registered count in response to changes in the count of said counter, and means to limit the change of said register to a selected time interval.

Claim 12

A digital tracker according to claim 9 wherein the repetition rate of said interrogation pulses is 1000 pulses per second.

Claim 13

A digital tracker according to claim 9 wherein said counting means includes a down counter coupled to said register, means for transferring the count of said register into said down counter, means to detect a zero count from said down counter, and clock means for controlling the rate of said down counter.

Claim 14

A digital tracker according to claim 11 including means for generating said fourth control signal responsive to said zero count means for rendering saId range gate means operative.

Claim 15

A digital tracker according to claim 12 including means for determining the time interval between said reply pulse and said range gate pulse, means responsive to said time interval for generating a delay pulse having a duration greater than said difference, and means responsive to said delay pulse to increase the increment of the least significant number of said range rate computation.

Claim 16

A digital tracker according to claim 7 including threshold means coupled to each of said two groups of taps to inhibit any reply pulse below a threshold value.

Claim 17

A digital tracker according to claim 9, wherein said register is limited before interrogation signal intervals to effect a change in the time count to + or - 100 nanoseconds, wherein 100 nanoseconds is equal to 1/120 nautical miles of range to said remote station.