Beacon tracking system

• US 4,021,807 A
• Filed: 04/02/1975
• Issued: 05/03/1977
• Est. Priority Date: 04/02/1975
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Culpepper, Jerry W., Currie, Harry A., Heathcock, William F.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Berger, Richard E.
• Application Number:
  US05/564,510
• Time in Patent Office: 762 Days
• Field of Search: 343/113 R, 343/112 R, 343/112 D, 325/111, 340/224, 340/280
• US Class Current: 342/458
• CPC Class Codes: G01S 2205/05 Anti-theft or abduction
• CPC Class Codes: G01S 5/02 using radio waves using satellite radio beacon systems for determining position G01S19/00
• CPC Class Codes: G07G 3/003 Anti-theft control theft alarms G08B13/00
• CPC Class Codes: G08B 13/14 by lifting or attempted removal of hand-portable articles

Abstract

A radio frequency transmitter is hidden within a packet of currency which may be mingled with other currency packets in the cash drawer of a bank, convenience store or other such commercial institution. The transmitter is automatically activated by unauthorized removal from the cash drawer or other place of safekeeping. The signals from the transmitter activate alarms in one or more receivers located in police vehicles in the area. The receivers employ phase comparison techniques to indicate relative direction and distance to the transmitter thereby facilitating apprehension of the possessor of the packet.

Claims

1. A single site beam tracking system comprising:

a. an article having a concealed compartment;

b. a miniature electromagnetic energy transmitter within the concealed compartment of the article, said transmitter including;

i. an oscillator having a frequency stabilizing means for providing a selected frequency stability;

ii. a frequency multiplier coupled to the oscillator for generating a higher harmonic of the oscillator frequency for signal discrimination in a noise environment;

iii. a switch; and

iv. a source of electrical power, said switch connected between the source of power and oscillator for controlling transmitter operation;

c. a storage means including a switch activator, said article stored within the storage means with the transmitter switch in operative association with the switch activator for maintaining the transmitter switch in an off position while the article is within the storage means;

d. a receiver means including first and second antennas mounted upon a vehicle in a selectively spaced relationship along a transverse axis thereof, a phase comparison circuit selectively coupled to the first and second antenna for comparing the phases of the signals received by said first and second antennas to determine the direction to said transmitter, and a signal amplitude measuring means connected to the phase comparison circuit for determining distance from receiver to transmitter; and

e. a display means including a direction indicator and a distance indicator for providing direction and distance information locating the transmitter bearing article.

2. A beacon tracking system comprising:

a. an article having a concealed compartment;

b. a miniature electromagnetic energy transmitter within the concealed compartment of the article, said transmitter including;

i. an oscillator having a frequency stabilizing means for providing a selected frequency stability,

ii. a frequency multiplier coupled to the oscillator for generating a higher harmonic of the oscillator frequency for signal discrimination in a noise environment,

iii. a switch, and

iv. a source of electrical power, said switch connected between the source of power and oscillator for controlling transmitter operation;

c. a storage means including a switch activator, said article stored within the storage means with the transmitter switch in operative association with the switch activator for maintaining the transmitter switch in an off position while the article is within the storage means;

d. an electromagnetic energy receiver having;

i. first and second antennas mounted upon a vehicle in a selectively spaced relationship along a transverse axis thereof;

ii. first and second conversion channels connected respectively, to the first and second antennas, said conversion channels each having a plurality of converter stages for reducing the received frequency to a frequency substantially that for obtaining maximum phase difference accuracy and an AGC feedback circuit for increasing the dynamic range of input signals;

iii. detector means connected to the first conversion channel for detecting the presence of the transmitted signal; and

iv. a phase detector means connected to the outputs of the first and second conversion channels for comparing received signals to determine the phase difference of the transmitted signals received by the first and second antennas; and

e. a display unit including;

i. an indicator for indicating the presence of the transmitted signal,

ii. a direction meter connected to the phase detector for indicating the side of the vehicle to which the antenna is located; and

iii. a distance indicator connected to the AGC circuit for indicating the distance to the transmitter responsively to the amplitude of the AGC signals, whereby the vehicle provides the operator a single site for beacon tracking.

3. A single site beacon tracking system comprising:

a. an article having a concealed compartment;

b. a minature radio transmitter compartment of the article, said transmitter including;

i. an oscillator having a frequency stability means for providing a selected frequency stability,

ii. a frequency multiplier coupled to the oscillator for generating a higher harmonic of the oscillator frequency for transmission,

iii. a modulator for modulating the carrier signal with a transmitter identifying frequency signal,

iv. a switch, and

v. a source of electrical power, said switch connected between the source of power and oscillator for controlling transmitter operation;

c. a storage means including a switch activator, said article stored within the storage means with the transmitter switch in operative association with the switch activator for maintaining the transmitter switch in an off position while the article is within the storage means;

d. an RF receiver having;

i. first, second and third antennas mounted upon a self propelled vehicle, the antennas forming the corners of a right triangle whose legs have a length less than one-half the wavelength at the carrier frequency of the transmitter, the first antenna being positioned at the intersection of a longitudinal axis and a transverse axis of the self propelled vehicle with the second and the third antennas being positoned, repectively, on the corresponding transverse and longitudinal axes of the vehicle,

ii. a switching means connected to the second and third antennas,

iii. a first triple conversion channel connected to the first antenna and a second triple conversion channel connected to the switching means of the second and third antennas, the switching means operative to connect selectively the second and third antennas to the second triple conversion channel, said first and second triple conversion channels including first, second and third converter stages for reducing the received frequency to a frequency substantially that for obtaining maximum phase difference accuracy and an AGC feedback circuit coupling the output of the second amplifier stage back to the first amplifier for increasing the dynamic range of input signals,

iv. an alarm detector coupled to the output of the second stage amplifier of the first triple conversion channel for detecting the presence of the transmitter identifying frequency signal in any incoming signal,

v. a phase detector coupled to the outputs of the first and second triple conversion channels for producing an analog signal having an amplitude proportional to the phase difference of the transmitted signals received, and

vi. a large angle detector coupled to said phase detector for producing, above a selected threshold, an on/off gating signal; and

e. a display unit including;

i. a switch selector coupled to the second and third antenna selector switch for switching the second triple conversion circuit from the second antenna to the third antenna;

ii. a direction meter including first and second circuits connected to the phase detector, said direction meter when the second antenna is connected to the second triple conversion channel having its first circuit connected to the detector for the meter to indicate the side of the vehicle to which the transmitter is located and when the third antenna is connected to the second triple conversion channel having its second circuit connected to the detector for indicating the end of the vehicle to which the transmitter is located,

iii. a front/rear lamp assembly including front and rear lamps connected to the phase detector and operative responsively to the third antenna input to light, selectively, the front and rear lamps to indicate whether the transmitter is in front of or behind the vehicle,

iv. a tone generator having input terminals connected to the AGC feedback circuit, alarm detector and large angle detector, the alarm detector activating the tone generator responsive to the presence of a signal having the transmitter identifying frequency, the amplitude of the AGC signal varying the frequency of the output of the tone generator to provide an audible tone indicating distance to the transmitter, and the large angle detector providing a gating signal to gate the tone generator on and off in a periodic fashion to indicate that a turn of the self propelled vehicle is required to track the transmitter,

v. a speaker connected to the output of the tone generator to produce sound waves indicative of the tone generator output, and

vi. a distance indicator connected to the AGC feedback circuit for visually indicating the distance to the transmitter responsively to the amplitude of the AGC signals.

4. A method for indicating removal of an item from its proper repository and for locating said item after said removal, said method comprising the steps of:

a. secreting a radio frequency energy transmitter in an item;

b. activating the radio frequency energy transmitter in response to removal of the item to transmit transmitter identifying signals;

c. receiving said radio frequency energy at a pair of antennas selectively mounted on a vehicle in a spaced relationship at less than about one-half wavelength of a carrier frequency of the transmitted radio frequency energy;

d. processing received radio frequency energy to detect the presence of the transmitted RF energy and to determine the phase of the radio frequency received at each of the pair of antennas and the amplitude of the radio frequency energy received at one of the pair of antennas;

e. comparing the phases of the transmitted radio frequency energy received by the antennas for determining the phase difference thereof; and

f. converting the phase difference signal and the amplitude of the RF energy received by one of the antennas, respectively, to direction and distance receivable signals for location of the transmitter by the operator of the vehicle.