System for locating mobile objects in distress

• US 4,240,079 A
• Filed: 08/24/1978
• Issued: 12/16/1980
• Est. Priority Date: 02/07/1978
• Status: Expired due to Term

• Current Assignee: Viktor A. Zhilin
• Original Assignee: Viktor A. Zhilin
• Inventors: Zhilin, Viktor A.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US05/936,648
• Time in Patent Office: 845 Days
• Field of Search: 343/100 ST
• US Class Current: 342/352
• CPC Class Codes: G01S 1/68 Marker, boundary, call-sign, or like beacons transmitting signals not carrying directional information
• CPC Class Codes: G01S 11/10 using Doppler effect

Abstract

A system for locating mobile objects in distress comprises emergency radio stations provided on the mobile objects and energized when these mobile objects are in distress, at least one low orbiting earth satellite for retransmission of the signals from the emergency stations, at least one control station for tracking the earth satellite and determining its ephemeris, and at least one receiving station connected with the control station by a communication link and designed for reproduction of the messages transmitted by the emergency stations and for location of the mobile craft. The emergency radio stations are divided into groups with a specified pattern of the two components of a phase-shift-keyed signal, alternating in accordance with the transmitted message, assigned to each group. The receiving station includes a receiver, a reference-frequency oscillator, a signal processing device, their number being equal to that of the groups of emergency stations, and a computer for calculation of the coordinates of the emergency stations, with the input of the computer connected to the communication link. Each of the signal processing devices comprises a first filter and a second filter matched with the first and the second components of the signal from one of the groups of emergency radio stations, respectively, and connected to the output of the receiver, first and second detectors with their inputs connected to the outputs of the first and second filters, respectively, an adder with the two inputs thereof connected, respectively, to the outputs of the first and second detectors, tracking systems provided with a second-order astaticism for measuring the running phase of the envelopes of the received signals from the emergency stations, one of the inputs of each tracking system being connected with the output of the reference-frequency oscillator, and one of its outputs being connected with the other input of the computer, gates with their number equal to that of the tracking systems, and decoders with their number also equal to that of the tracking systems, for decoding the messages transmitted by the emergency stations. The signal inputs of the gates are connected to the output of the adder, the output of each of the gates is connected with the other input of one of the tracking systems, the inhibit inputs of each gate being connected with the other outputs of the remaining tracking systems. Two inputs of each of the decoders are connected to the outputs of the first and second detectors, respectively, while the control input of each decoder is connected with the other output of one of the tracking systems. The proposed system provides the capability of simultaneous operation of a large number of emergency radio stations within one common frequency band.

Claims

1. A system for location of mobile objects in distress comprising:

emergency radio stations each provided on one of the mobile objects and energized in the event of trouble with said mobile objects for transmission of distress messages by means of phase-shift-keyed signals occupying the common frequency band and representing a sequence of two components alternating in accordance with the message transmitted, said emergency radio stations being subdivided into groups each having a particular pattern of each of said components of said phase-shift-keyed signal;

at least one low orbiting earth satellite for retransmission of the signals emitted by said emergency radio stations;

at least one receiving station for reception of the signals retransmitted by said low orbiting earth satellite, reproduction of transmitted messages, and location of said mobile objects;

at least one control station for tracking of said earth satellite and measurement of the ephemeris thereof;

a communication link for connection of said receiving station with said control station;

said receiving station comprises a receiving antenna, a receiver having an input and an output, said input of said receiver being connected to said receiving antenna, a reference-frequency oscillator having an output, a plurality of signal processing means equal in number to said groups of emergency radio stations, and a computer for calculation of the coordinates of said emergency radio stations having a first input and a second input, said first input of said computer being connected with said communication link;

each of said signal processing means comprising;

a first filter and a second filter matched to said first and second components, respectively, of the signals emitted by the emergency radio stations belonging to one of said groups of said emergency radio stations, each of said filters having an input connected with said output of said receiver, and an output;

a first detector and a second detector each having an input and an output, said inputs of said first and second detectors being connected with said outputs of said first and second filters, respectively;

an adder having a first input and a second input and an output, said first and second inputs of said adder being connected with said outputs of said first and second detectors, respectively;

tracking systems with a second-order astaticism for measurement of the running phase of the envelopes of the signals received from said emergency radio stations, each of said tracking systems having a first and a second input and a first and a second output;

said first inputs of said tracking systems being connected with said output of said reference-frequency oscillator;

said first outputs of said tracking systems being connected with said second input of said computer;

gates equal in number to said tracking systems, said gates each having a signal input, inhibit inputs with their number equal to the number of said tracking systems minus one, and an output, said signal input of each of said gates being connected to said input of said adder, said output of each of said gates being connected to said second input of one of said tracking systems, said inhibit inputs of each of said gates being connected with said second outputs of the remaining tracking systems, respectively; and

decoders for decoding of the messages transmitted by said emergency radio stations, the number of said decoders being equal to that of said tracking systems, each of said decoders having a first input, a second input, and a control input, said first and second inputs of each of said decoders being connected with said outputs of said first and second detectors, respectively, said control input of each of said decoders being connected with said second output of one of said tracking systems.

2. A system as defined in claim 1, further comprising at least one geostationary satellite for retransmission of signals from said low orbiting earth satellite to said receiving station.

3. A system as defined in claim 1, wherein each of said signal processing means further comprises additional gates equal in number to said tracking systems, said gates each having number being equal to that of said tracking systems minus one;

and wherein the control input of each of said decoders is connected with said second output of one of said tracking systems via one of said additional gates, the inhibit inputs of each of said additional gates being connected to said second outputs of the remaining tracking systems, respectively.

4. A system, as defined in claim 1, wherein each of said tracking systems comprises:

a frequency divider with two values of the division ratio, having a first and a second input and an output, the first value of the division ratio ensuring a repetition period of the signals from said output of said frequency divider smaller than the repetition period of the signals emitted by said emergency radio stations, the second value of the division ratio ensuring a repetition period of the signals from said output of said frequency divider equal to the repetition period of the signals emitted by said emergency radio stations;

a tracking strobe and selector pulse shaper having an input, a first output and a second output, said input of said tracking strobe and selector pulse shaper being connected with said output of said frequency divider;

a gate having a signal input, an enable input, and an output, said signal input of said gate being connected with said first output of said tracking strobe and selector pulse shaper, said output of said gate representing said second output of said tracking system;

a time discriminator for generation of a misalignment voltage depending on the time shift between the tracking strobes and the signal from said output of said adder, said time discriminator having a first input, a second input, and an output, said first input of said time discriminator representing said second input of said tracking system, said second input of said time discriminator being connected with said second output of said tracking strobe and selector pulse shaper;

a feedback circuit including a first integrator having an input connected to said output of said time discriminator and an output, an amplifier having an input connected to said output of said time discriminator, and an output, an adding network having two inputs of which the first one is connected with said output of said first integrator, while the second one is connected with said output of said amplifier, and an output, and a second integrator having an input connected to said output of said adding network and an output;

a phase shifter for shifting of the tracking strobes according to the magnitude of the signal from said output of said second integrator in said feedback circuit, said phase shifter having a first and a a second input and an output, said first input of said phase shifter representing said first input of said tracking system, said second input of said phase shifter being connected with said output of said second integrator in said feedback circuit, said output of said phase shifter being connected to said first input of said frequency divider;

a phase meter for measurement of the amount of displacement of the tracking strobes which determines the running phase of the envelope of the signal received from one of said emergency radio stations, said phase meter having a first input, a second input, a third input, and an output, said first input of said phase meter being connected to said first input of said phase shifter, said second input of said phase meter being connected with said output of said phase shifter, said output of said phase meter representing said first output of said tracking system; and

a control circuit for generation of a control signal defining said second value of the division ratio of said frequency divider, said control circuit including a coincidence circuit, an integrating circuit, and a high input impedance amplifier connected in series, said coincidence circuit having two inputs, the first input being connected with said first output of said tracking strobe and selector pulse shaper, and the second input being connected with said first input of said time discriminator, said amplifier of said control circuit having an output connected with said second input of said frequency divider, with said third input of said phase meter, and with said enable input of said gate.

5. A system as defined in claim 2, wherein each of said signal processing means further comprises additional gates with their number equal to that of said tracking systems, said additional gates each having inhibit inputs equal in number to said tracking systems minus one;

and wherein the control input of each of said decoders is connected with said second output of one of said tracking systems via one of said additional gates, the inhibit inputs of each of said additional gates being connected to said second outputs of the remaining tracking systems, respectively.

6. A system as defined in claim 5, wherein each of said tracking systems comprises:

a frequency divider with two values of the division ratio having a first input, a second input, and an output, the first value of the division ratio ensuring a repetition period of the signals from said output of said frequency divider smaller than the repetition period of the signals emitted by said emergency radio stations, the second value of the division ratio ensuring a repetition period of the signals from said output of said frequency divider equal to the repetition period of the signals emitted by said emergency radio stations;

a tracking strobe and selector pulse shaper having an input, a first output and a second output, said input of said tracking strobe and selector pulse shaper being connected with said output of said frequency divider;

a gate having a signal input, an enable input, and an output;

said signal input of said gate being connected with said first output of said tracking strobe and selector pulse shaper, said output of said gate representing said second output of said tracking system;

a time discriminator for generating a misalignment voltage depending on the time shift between the tracking strobes and the signals from said output of said adder, said time discriminator having a first input, a second input, and an output, said first input of said time discriminator representing said second input of said tracking system, said second input of said time discriminator being connected with said second output of said tracking strobe and selector pulse shaper;

a feedback circuit including a first integrator having an input connected with said output of said time discriminator and an output, an amplifier having an input connected to said output of said time discriminator and an output, an adding network having two inputs, the first input being connected with said output of said first integrator and the second output being connected with said output of said amplifier, and an output, and a second integrator connected to said output of said adding network, and an output;

a phase shifter for shifting of tracking strobes according to the magnitude of the signal from said output of said second integrator in said feedback circuit, said phase shifter having a first input, a second input, and an output, said first input of said phase shifter representing said first input of said tracking system, said second input of said phase shifter being connected with said output of said second integrator in said feedback circuit, said output of said phase shifter being connected to said second input of said frequency divider;

a phase meter for measurement of the amount of displacement of the tracking strobes which determines the running phase of the envelope of the signal received from one of said emergency radio stations, said phase meter having a first input, a second input, a third input, and an output, said first input of said phase meter being connected to said first input of said phase shifter, said second input of said phase meter being connected to said output of said phase shifter, said output of said phase meter representing said first output of said tracking system; and

a control circuit for generation of a control signal defining said second value of the division ratio, said control circuit including a coincidence circuit, an integrating circuit and a high input impedance amplifier connected in series, said coincidence circuit having two inputs, the first input being connected with said first output of said tracking strobe and selector pulse shaper and the second input being connected with said first input of said time discriminator, said amplifier of said control circuit having an output connected with said second input of said frequency divider, with said third input of said phase meter, and with said enable input of said gate.