Method of and apparatus for locating predetermined portions of a radio-frequency pulse, particularly adapted for leading edge location of loran and similar navigational pulses

Claim 3

A method as claimed in claim 1 and in which the continued said forward sampling is effected until the end of the predetermined cycle is reached.

Claim 4

A method as claimed in claim 1 and in which the continued said forward sampling is effected by obtaining the derivative of the pulse envelope signal information and combining the pulse envelope signal information with its derivative to obtain a null point, and varying the position of such null point forwardly along the successive cycles under the pulse envelope.

Claim 5

A method as claimed in claim 1 and in which said sampling backwardly is effected while receiving the signal information over a relatively narrow band compared with a relatively wide band of receiving during the forward sampling.

Claim 6

A method as claimed in claim 1 and in which said searching is limited to a predetermined search time, after which, if no signal information has been located, the searching is repeated for said predetermined search time over a wider band, after which, if no signal information has been located, said searching is effected for successive search times, each advanced in time from the previous.

Claim 7

A method as claimed in claim 1 and in which said searching is limited to a predetermined search time, after which, if no signal information has been located, said searching is effected for successive search times each aDvanced in time from the previous.

Claim 8

A method as claimed in claim 1 and in which said predetermined cycle is located in the leading edge of the transmitted pulse envelope.

Claim 9

A method as claimed in claim 7 and in which said transmitted pulse envelope comprises a Loran radio-frequency carrier navigation pulse which is transmitted via ground and sky waves such that the monitoring and searching involves the reception of an initial ground-wave pulse envelope and a subsequent contaminating overlapping sky-wave pulse envelope.

Claim 10

A method as claimed in claim 8 and in which said predetermined cycle is the third cycle under the leading edge of the ground-wave pulse envelope and each of the first-named predetermined time intervals is substantially three times the period of said cycle, and each of the said narrower predetermined time intervals is substantially equal to the period of said cycle.

Claim 11

A method as claimed in claim 8 and in which said sampling backwardly is effected while receiving the signal information over a relatively narrow band compared with a relatively wide band of receiving during the forward sampling.

Claim 12

A method as claimed in claim 10 and in which said narrow and wide bands are respectively adjusted to accommodate for the maximum and minimum time separations, respectively, of ground and sky-wave pulses.

Claim 13

A method as claimed in claim 8 and in which the continued said forward sampling is effected until the end of the predetermined cycle is reached.

Claim 14

A method as claimed in claim 12 and in which nulling is effected at the end of the predetermined cycle by sampling ahead of the same and comparing with sampling behind the same.

Claim 15

A method as claimed in claim 8 and in which the continued said forward sampling is effected by obtaining the derivative of the pulse envelope signal information and combining the pulse envelope signal information with its derivative to obtain a null point, and varying the position of such null point forwardly along the successive cycles under the pulse envelope.

Claim 16

Radio-frequency pulse envelope tracking apparatus having, in combination, means for receiving radio-frequency signal pulse information and for determining when received signal information reaches a threshold; means connected with the receiving and determining means for thereupon sampling the signal information backwardly in predetermined successive time intervals relatively wide compared with the cycle period of the radio frequency until no signal information is detected; means connected with the receiving and determining means for thereafter sampling forwardly in narrower predetermined successive time intervals until signal information is detected; and means cooperative with the last-named means for continuing the forward sampling to a predetermined cycle within said envelope and for locking thereupon.

Claim 17

Radio-frequency pulse envelope tracking apparatus having, in combination, means for receiving radio-frequency signal pulse information and for determining when received signal information reaches a threshold; means connected with the receiving and determining means for thereupon sampling the signal information backwardly in predetermined successive time intervals relatively wide compared with the cycle period of the radio frequency until no signal information is detected; means connected with the receiving and determining means for thereafter sampling forwardly in narrower predetermined successive time intervals until signal information is detected; and means cooperative with the last-named means for continuing the forward sampling to a predetermined cycle within said envelope and for locking thereupon.

Claim 18

Radio-frequency pulse envelope tracking apparatus as claimed in claim 15 and in which said radio-frequency signal information comprises ground and sky-wave transmitted navigation pulses, the latter of which is delayed with respect to the onset of the former but overlaps the same, with said predetermined cycle being selected within the leading edge of the former in advance of such overlap, and in which said receiving means comprises means for receiving such pulses.

Claim 19

Radio-frequency pulse envelope tracking apparatus as claimed in claim 15 and in which said locking means comprises means for locking upon the end of such predetermined cycle.

Claim 20

Radio-frequency pulse envelope tracking apparatus as claimed in claim 15 and in which said continuing sampling means comprises means for obtaining the derivative of the pulse envelope signal information and combining the pulse envelope signal information with its derivative to obtain a null point, and means for adjusting the position of such null point forwardly along the successive cycles under the pulse envelope to said predetermined cycle.

Claim 21

Radio-frequency pulse enveloPe tracking apparatus as claimed in claim 15 and in which timing means is provided for timing the search time during which said signal is less than said threshold and, after a predetermined search time, for widening the receiving band of said receiving means.

Claim 22

Radio-frequency pulse envelope tracking apparatus as claimed in claim 19 and in which means is provided, operable in the event that the widened band searching over a predetermined search time has resulted in no received signal reaching said threshold, for thereupon continuing such searching over such successive search times, each advanced in time from the previous.

Claim 23

Radio-frequency pulse envelope tracking apparatus as claimed in claim 15 and in which said receiving and determining means comprise radio-frequency amplifying means connected through sample-and-hold circuit means to analog-to-digital converter means having phase lock and quadrature data outputs, a phase-lock loop, said phase lock loop data output being connected through said phase-lock loop to means for advancing or retarding the sample-and-hold circuit means, and said quadrature data output being connected through limited band integrating means with threshold detector means.

Claim 24

Radio-frequency pulse envelope tracking apparatus as claimed in claim 21 and in which said backward and forward sampling means comprise cycle selection means connected with said radio-frequency amplifying means for obtaining the derivative of the received pulse envelope signal information and for combining the pulse envelope signal information with its derivative to obtain a null point and having means for adjusting the position of such null point forwardly along the successive cycles under the pulse envelope to said predetermined cycle; further sample-and-hold circuit means connected to said cycle selection means and feeding further analog-to-digital converter means; and further integrator and threshold detector means connected with said further analog-to-digital converter means for advancing or retarding the first-named sample and hold means.

Claim 25

Radio-frequency pulse envelope tracking apparatus as claimed in claim 21 and in which there is provided search timing means, gate means connected with said threshold detector means and controlled by said search timing means, front edge location sequencer means and retard and advance logic circuit means, said gate means being connected through said front edge location sequencer means and said retard and advance logic circuit means to control said phase lock loop.

Claim 26

Radio-frequency pulse envelope tracking apparatus as claimed in claim 23 and in which said phase lock loop comprises oscillator means feeding divider chain means, in turn connected with said sample and hold circuit means.

Claim 27

Radio-frequency pulse envelope tracking apparatus as claimed in claim 23 and in which said front edge location sequencing means is provided with an output connected with said radio-frequency amplifying means to change the bandwidth thereof in response to the output of said threshold detector and gate means.