US3889260A — Analog echo protection circuit for DME

Claim 1

Independent Claim 260 words

In a distance measuring system of the type which transmits a series of interrogation pulses toward a remote beacon and receives a stream of pulses from said beacon including reply pulses synchronized with said interrogation pulses; the improvement comprises the combination therewith of apparatus for determining, within a given range interval, the position of a set of synchronized reply pulses; said apparatus comprising: a. first means including a first timer initially set to a time t1, where t1 has a given value corresponding to a certain range within said given range interval, for determining and storing, in response to solely a first single interrogation pulse, a measure of the time t2 corresponding to the range of the first received reply pulse which occurs after time t1; b. second means including a second timer for determining in response to at least one interrogation pulse subsequent to said first interrogation pulse whether reply pulses continue to occur substantially at time t2; and c. third means coupled to said first and second means and responsive to the failure of said reply pulses to continue to occur for causing said first means to determine and store in response to solely the next following single interrogation pulse a measure of the time t3 corresponding to the range of the first received reply pulse which occurs after time t2, said third means being responsive only to the continuation of occurrence of said reply pulses for deriving an output signal indicating that said reply pulses which continue to occur are reply pulses synchronized with said interrogation pulses.

Claim 2

Dependent Claim 260 words

In a distance measuring system of the type which transmits a series of interrogation pulses toward a remote beacon and receives a stream of pulses from said beacon including reply pulses synchronized with said interrogation pulses; the improvement comprises the combination therewith of apparatus for determining, within a given range interval, the position of a set of synchronized reply pulses; said apparatus comprising: a. first means including a first timer initially set to a time t1, where t1 has a given value corresponding to a certain range within said given range interval, for determining and storing, in response to solely a first single interrogation pulse, a measure of the time t2 corresponding to the range of the first received reply pulse which occurs after time t1; b. second means including a second timer for determining in response to at least one interrogation pulse subsequent to said first interrogation pulse whether reply pulses continue to occur substantially at time t2; and c. third means coupled to said first and second means and responsive to the failure of said reply pulses to continue to occur for causing said first means to determine and store in response to solely the next following single interrogation pulse a measure of the time t3 corresponding to the range of the first received reply pulse which occurs after time t2, said third means being responsive only to the continuation of occurrence of said reply pulses for deriving an output signal indicating that said reply pulses which continue to occur are reply pulses synchronized with said interrogation pulses.

Claim 3

Dependent Claim 72 words

The combination as set forth in claim 1, wherein said distance measuring system is tracking a set of reply pulses and where said set of synchronized reply pulses, if present, are valid reply pulses, and where there is further included a means responsive to said output signal to cause said distance measuring system to stop tracking the set of reply pulses it is tracking and to search for said valid reply pulses.

Claim 4

Dependent Claim 269 words

Apparatus for distinguishing synchronized reply pulses from random reply pulses, comprising in combination: means producing a series of spaced apart reference pulses each marking the start of a cycle; means producing a series of reply pulses, some of which are synchronized in time relative to said reference pulses and some of which are random relative thereto; timing means storing a signal indicative of time, t, between receipt of one reference pulse and a reply pulse in the same cycle; means producing a range gate pulse at time, t, in the N successive cycles next following the one in which said one reference pulse occurred, where N is a fixed integer greater than zero; means responsive to the absence of any reply pulses during the presence of said N range gate pulses, being indicative that said reply pulse being timed was a random reply pulse, for causing said timing means to time until another reply pulse is received during the Nth cycle following the one in which said one reference pulse occurred and then to store that new time, t'', which represents the time of occurrence of said another reply pulse in its cycle; said means for producing range gate pulses producing N additional range gate pulses at time, t'', during the N cycles following the one in which said aNother pulse was produced; and means responsive to the presence of a reply pulse during at least Y of said times said N additional range gate pulses are present for indicating said another reply pulse is a synchronized reply pulse, where Y is a preselected integer not greater than N.

Claim 5

Dependent Claim 269 words

Apparatus for distinguishing synchronized reply pulses from random reply pulses, comprising in combination: means producing a series of spaced apart reference pulses each marking the start of a cycle; means producing a series of reply pulses, some of which are synchronized in time relative to said reference pulses and some of which are random relative thereto; timing means storing a signal indicative of time, t, between receipt of one reference pulse and a reply pulse in the same cycle; means producing a range gate pulse at time, t, in the N successive cycles next following the one in which said one reference pulse occurred, where N is a fixed integer greater than zero; means responsive to the absence of any reply pulses during the presence of said N range gate pulses, being indicative that said reply pulse being timed was a random reply pulse, for causing said timing means to time until another reply pulse is received during the Nth cycle following the one in which said one reference pulse occurred and then to store that new time, t'', which represents the time of occurrence of said another reply pulse in its cycle; said means for producing range gate pulses producing N additional range gate pulses at time, t'', during the N cycles following the one in which said aNother pulse was produced; and means responsive to the presence of a reply pulse during at least Y of said times said N additional range gate pulses are present for indicating said another reply pulse is a synchronized reply pulse, where Y is a preselected integer not greater than N.

Claim 6

Dependent Claim 95 words

The combination as set forth in claim 3, wherein means for causing said timing means to time comprises a counter, means responsive to said a reply pulse for energizing said counter, means responsive to each of the following reference pulses for altering the count in said counter by a unit value, and means responsive to the counter having been altered by a count of N times said unit value and by the concurrent presence of the next following said range gate pulse for causing said timing means to time until another reply pulse is received.

Claim 7

Dependent Claim 69 words

The combination as set forth in claim 3, wherein said means producing a range gate pulse comprises a second timing means producing a signal indicative of the time following each reference pulse and a comparison means for comparing the signal from said timing means indicative of time, t, and the signal from said second time indicating means for producing a range gate pulse when said signals indicate equal time.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1978-06-09	1978-12-09	1979-06-10	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1982-06-09	1982-12-09	1983-06-10	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1986-06-09	1986-12-09	1987-06-10	$7700.00	Window Closed / Lapsed

Analog echo protection circuit for DME

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