Radio receiver for use in a radio tracking system and a method of operation thereof

• US 5,722,059 A
• Filed: 12/06/1995
• Issued: 02/24/1998
• Est. Priority Date: 02/24/1995
• Status: Expired due to Term

• Current Assignee: NTP Incorporated
• Original Assignee: NTP Incorporated
• Inventors: Campana, Thomas J. Jr.
• Primary Examiner(s): Mullen, Thomas
• Application Number:
  US08/568,416
• Time in Patent Office: 811 Days
• Field of Search: 340/573, 340/574, 340/815.45, 340/825.69, 340/825.14, 340/825.2, 375/202, 371/47.1, 455/49.1, 455/53.1, 455/159.2, 455/269, 455/347, 455/351, 455/226.2, 455/226.4
• US Class Current: 455/226.2
• CPC Class Codes: G08B 21/0222 Message structure or message content, e.g. message protocol
• CPC Class Codes: G08B 21/0227 System arrangements with a plurality of child units
• CPC Class Codes: G08B 21/023 Power management, e.g. system sleep and wake up provisions
• CPC Class Codes: G08B 21/0247 System arrangements wherein the alarm criteria uses signal strength
• CPC Class Codes: G08B 21/0263 System arrangements wherein the object is to detect the direction in which child or item is located
• CPC Class Codes: H04B 17/18 Monitoring during normal operation
• CPC Class Codes: H04B 17/23 Indication means, e.g. displays, alarms, audible means
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0072 Error control for data other than payload data, e.g. control data
• CPC Class Codes: H04L 1/20 using signal quality detector

Abstract

A method and radio receiver for determining where at least one frequency hopping radio frequency transmitter is located with respect to a set range measured from a synchronized frequency hopping radio frequency receiver. Each frequency hopping radio frequency transmitter periodically transmits an identification code containing a plurality of digits which identifies each frequency hopping radio frequency transmitter. The synchronized frequency hopping radio frequency receiver determines if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, calculates an integral of a received signal strength indicator of each radio frequency carrier determined to contain at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computes an average of the calculated integrals, compares the average of the calculated integrals to a numerical value representing the set range and generates an alert when the comparison reveals that at least one of the at least one frequency hopping radio frequency transmitter is outside the set range.

Claims

1. A method for determining where at least one frequency hopping radio frequency transmitter is located with respect to a set range measured from a synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identifies each frequency hopping radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

in response to receiving each radio frequency carrier, determining if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, calculatinq an integral of a received signal strength indicator of each radio frequency carrier determined to contain at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computing an average of the calculated integrals which is updated to include newly calculated integrals only when each newly calculated integral differs from the computed average of the calculated integrals by less than a function of the average of the calculated integrals so as to exclude from the computation of the average of the calculated integrals newly calculated integrals which differ from the average of the calculated integrals by more than the function, comparing the average of the calculated integrals to a numerical value representing the set range and qenerating an alert when the comparison reveals that at least one of the at least one frequency hopping radio frequency transmitter is outside the set range.

2. A method in accordance with claim 1 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radlo frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

3. A method in accordance with claim 1 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one frequency hopping radio frequency transmitter which contains at least part of the digits of the identification code of the one frequency hopping radio frequency transmitter and an alert which signals to a user of the synchronized frequency hopping radio frequency receiver that the user of the frequency hopping one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one frequency hopping radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the alert was transmitted and in response to the synchronized frequency hopping radio frequency receiver being moved by a user the synchronized frequency hopping radio frequency receiver displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of the radio frequency carrier from the frequency hopping radio frequency transmitter from which the alert was received to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the frequency hopping radio frequency transmitter transmitting the alert, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which transmitted the alert is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

4. A method in accordance with claim 1 wherein:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, produces each received signal strength indicator.

5. A method in accordance with claim 4 wherein:

the amplifier is an intermediate frequency amplifier.

6. A method for determining where at least one frequency hopping radio frequency transmitter is located with respect to a set range measured from a synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identifies each frequency hopping radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

in response to receiving each radio frequency carrier, determining if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, calculating an integral of a received signal strength indicator of each radio frequency carrier determined to contain at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computing an average of the calculated integrals which is updated to include newly calculated integrals, comparing the average of the calculated integrals to a numerical value representing the set range and generating an alert when the comparison reveals that at least one of the at least one frequency hopping radio frequency transmitter is outside the set range.

7. A method in accordance with claim 6 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

8. A method in accordance with claim 6 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one frequency hopping radio frequency transmitter which contains at least part of the digits of the identification code of the one frequency hopping radio frequency transmitter and an alert which signals to a user of the synchronized frequency hopping radio frequency receiver that the user of the frequency hopping one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one frequency hopping radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the alert was transmitted and in response to the synchronized frequency hopping radio frequency receiver being moved by a user the synchronized frequency hopping radio frequency receiver displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of the radio frequency carrier from the frequency hopping radio frequency transmitter from which the alert was received to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the frequency hopping radio frequency transmitter transmitting the alert, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which transmitted the alert is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

9. A method in accordance with claim 6 wherein:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, produces each received signal strength indicator.

10. A method in accordance with claim 9 wherein:

the amplifier is an intermediate frequency amplifier.

11. A method for determining where at least one frequency hopping radio frequency transmitter is located with respect to a set range measured from a synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identifies each radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

in response to receiving each radio frequency carrier, determining if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, producing a received signal strength indicator of each radio frequency carrier determined to contain at least part of the bits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computing an average of the received signal strength indicators, comparing the average of the received signal strength indicators to a value representing the set range and generating an alert when the comparison reveals that at least one of the at least one frequency hopping radio frequency transmitter is outside the set range.

12. A method in accordance with claim 11 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

13. A method in accordance with claim 11 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one frequency hopping radio frequency transmitter which contains at least part of the digits of the identification code of the one frequency hopping radio frequency transmitter and an alert which signals to a user of the synchronized frequency hopping radio frequency receiver that the user of the frequency hopping one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one frequency hopping radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the alert was transmitted and in response to the synchronized frequency hopping radio frequency receiver being moved by a user the synchronized frequency hopping radio frequency receiver displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of the radio frequency carrier from the frequency hopping radio frequency transmitter from which the alert was received to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the frequency hopping radio frequency transmitter transmitting the alert, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which transmitted the alert is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

14. A method in accordance with claim 11 wherein:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, produces each received signal strength indicator.

15. A method in accordance with claim 14 wherein:

the amplifier is an intermediate frequency amplifier.

16. A frequency hopping radio frequency receiver for determining where at least one frequency hopping radio frequency transmitter is located after synchronization between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter with respect to a set range measured from the synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identifies each frequency hopping radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

the frequency hopping radio frequency receiver having a processor, the processor in response to receiving each radio frequency carrier controls synchronization of frequency hopping between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter, determines if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, calculates an integral of a received signal strength indicator of each radio frequency carrier determined to contain at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computes an average of the calculated integrals which is updated to include newly calculated integrals only when each newly calculated integral differs from the computed average of the calculated integrals by less than a function of the average of the calculated integrals so as to exclude from the computation of the average of the calculated integrals newly calculated integrals which differ from the average of the calculated integrals by more than the function, compares the average of the calculated integrals to a value representing the set range and generates an alert when the comparison reveals that the at least one frequency hopping radio frequency transmitter is outside the set range.

17. A frequency hopping radio frequency receiver in accordance with claim 16 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

18. A frequency hopping radio frequency receiver in accordance with claim 16 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one frequency hopping radio frequency transmitter which contains at least part of the digits of the identification code of the one frequency hopping radio frequency transmitter and an alert which signals to a user of the synchronized frequency hopping radio frequency receiver that the user of the frequency hopping one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one frequency hopping radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the alert was transmitted and in response to the synchronized frequency hopping radio frequency receiver being moved by a user the synchronized frequency hopping radio frequency receiver displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of the radio frequency carrier from the frequency hopping radio frequency transmitter from which the alert was received to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the frequency hopping radio frequency transmitter transmitting the alert, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which transmitted the alert is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

19. A frequency hopping radio receiver in accordance with claim 16 further comprising:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, for producing each received signal strength indicator.

20. A frequency hopping radio frequency receiver in accordance with claim 19 wherein:

the amplifier is an intermediate frequency amplifier.

21. A frequency hopping radio frequency receiver for determining where at least one frequency hopping radio frequency transmitter is located after synchronization between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter with respect to a set range measured from the synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identify each frequency hopping radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

the frequency hopping radio frequency receiver having a processor, the processor in response to receiving each radio frequency carrier controls synchronization of frequency hopping between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter, determines if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, calculates an integral of a received signal strength indicator of each radio frequency carrier determined to contain at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computes an average of the calculated integrals which is updated to include newly calculated integrals, compares the average of the calculated integrals to a numerical value representing the set range and generates an alert when the comparison reveals that at least one of the at least one frequency hopping radio frequency transmitter is outside the set range.

22. A radio frequency receiver in accordance with claim 21 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hofromg radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

23. A radio frequency receiver in accordance with claim 21 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one frequency hopping radio frequency transmitter which contains at least part of the digits of the identification code of the one frequency hopping radio frequency transmitter and an alert which signals to a user of the synchronized frequency hopping radio frequency receiver that the user of the frequency hopping one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one frequency hopping radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the alert was transmitted and in response to the synchronized frequency hopping radio frequency receiver being moved by a user the synchronized frequency hopping radio frequency receiver displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of the radio frequency carrier from the frequency hopping radio frequency transmitter from which the alert was received to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the frequency hopping radio frequency transmitter transmitting the alert, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which transmitted the alert is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

24. A frequency hopping radio receiver in accordance with claim 21 further comprising:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, for producing each received signal strength indicator.

25. A frequency hopping radio frequency receiver in accordance with claim 21 wherein:

the amplifier is an intermediate frequency amplifier.

26. A frequency hopping radio frequency receiver for determining where at least one frequency hopping radio frequency transmitter is located after synchronization between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter with respect to a set range measured from the synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identifies each frequency hopping radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

the frequency hopping radio frequency receiver having a processor, the processor in response to receiving each radio frequency carrier controls synchronization of frequency hopping between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter, determines if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, produces a received signal strength indicator of each radio frequency carrier determined to contain at least part of the diqits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computes an average of the received signal strength indicators, compares the average of the received signal strength indicators to a numerical value representing the set range and generates an alert when a comparison reveals that at least one of the at least one frequency hopping radio frequency transmitter is outside the set range.

27. A frequency hopping radio frequency receiver in accordance with claim 26 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

28. A frequency hopping radio frequency receiver in accordance with claim 26 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one frequency hopping radio frequency transmitter which contains at least part of the digits of the identification code of the one frequency hopping radio frequency transmitter and an alert which signals to a user of the synchronized frequency hopping radio frequency receiver that the user of the frequency hopping one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one frequency hopping radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the alert was transmitted and in response to the synchronized frequency hopping radio frequency receiver being moved by a user the synchronized frequency hopping radio frequency receiver displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of the radio frequency carrier from the frequency hopping radio frequency transmitter from which the alert was received to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the frequency hopping radio frequency transmitter transmitting the alert, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which transmitted the alert is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

29. A frequency hopping radio receiver in accordance with claim 26 further comprising:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, for producing each received signal strength indicator.

30. A frequency hopping radio frequency receiver in accordance with claim 29 wherein:

the amplifier is an intermediate frequency amplifier.

31. A method for determining where at least one frequency hopping radio frequency transmitter is located with respect to a set range measured from a synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identifies each frequency hopping radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

in response to receiving each radio frequency carrier, determining if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, producing a function of a received signal strength indicator of each radio frequency carrier determined to contain at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computing a function in response to at least one function of the received signal strength indicator, comparing the computed function to a numerical value representing the set range and generating an alert when the comparison reveals that at least one of the at least one frequency hopping radio frequency transmitter is outside the set range.

32. A method in accordance with claim 31 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

33. A method in accordance with claim 31 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

34. A method in accordance with claim 31 wherein:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, produces each received signal strength indicator.

35. A method in accordance with claim 34 wherein:

the amplifier is an intermediate frequency amplifier.

36. A method in accordance with claim 34 wherein:

the computed function is responsive to a plurality of produced functions of the received signal strength indicator.

37. A method in accordance with claim 31 wherein:

the computed function is responsive to a plurality of produced functions of the received signal strength indicator.

38. A frequency hopping radio frequency receiver for determining where at least one frequency hopping radio frequency transmitter is located after synchronization between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter with respect to a set range measured from the synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits which identifies each frequency hopping radio frequency transmitter with a radio frequency carrier modulated with a subcarrier with the subcarrier being modulated with the identification code comprising:

the frequency hopping radio frequency receiver having a processor, the processor in response to receiving each radio frequency carrier controls synchronization of frequency hopping between the frequency hopping radio frequency receiver and the at least one frequency hopping radio frequency transmitter, determines if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, produces a function of a received signal strength indicator of each radio frequency carrier determined to contain at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter, computes a function in response to at least one function of the received signal indicator, compares the computed function to a value representing the set range and generates an alert when the comparison reveals that the at least one frequency hopping radio frequency transmitter is outside the set range.

39. A frequency hopping radio receiver in accordance with claim 38 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each frequency hopping radio frequency transmitter which is used to compute the average of the calculated integrals; and

after generation of the alert using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the identification codes were transmitted which caused generation of the alert and in response to the synchronized frequency hopping radio frequency receiver being moved by a user, displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of transmissions of the radio frequency carrier containing at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted which caused the synchronized frequency hopping radio frequency receiver to generate the alert to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier containing the at least part of the digits of the identification code of the frequency hopping radio frequency transmitter from which the identification code was transmitted to generate the alert is received, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which is outside of the set range is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

40. A frequency hopping radio receiver method in accordance with claim 38 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one frequency hopping radio frequency transmitter which contains at least part of the digits of the identification code of the one frequency hopping radio frequency transmitter and an alert which signals to a user of the synchronized frequency hopping radio frequency receiver that the user of the frequency hopping one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one frequency hopping radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier containing at least part of the digits of the identification code identifying the frequency hopping radio frequency transmitter from which the alert was transmitted and in response to the synchronized frequency hopping radio frequency receiver being moved by a user the synchronized frequency hopping radio frequency receiver displaying a magnitude of the integral of each successively received signal strength indicator generated in response to reception of the radio frequency carrier from the frequency hopping radio frequency transmitter from which the alert was received to permit a user of the synchronized frequency hopping radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the frequency hopping radio frequency transmitter transmitting the alert, producing a maximum magnitude of the integral of each successively received signal strength indicator relative to the synchronized frequency hopping radio frequency receiver whereby a direction of the frequency hopping radio frequency transmitter which transmitted the alert is determined by the user of the synchronized frequency hopping radio frequency receiver relative to the synchronized frequency hopping radio frequency receiver.

41. A frequency hopping radio receiver in accordance with claim 38 further comprising:

an amplifier, responsive to each radio carrier modulated with the subcarrier containing the identification of one of the at least one radio frequency transmitter, for producing each received signal strength indicator.

42. A frequency hopping radio frequency receiver in accordance with claim 41 wherein:

the amplifier is an intermediate frequency amplifier.

43. A frequency hopping radio frequency receiver in accordance with claim 41 wherein:

the computed function is responsive to a plurality of produced functions of the received signal strength indicator.

44. A frequency hopping radio frequency receiver in accordance with claim 38 wherein:

the computed function is responsive to a plurality of produced functions of the received signal strength indicator.

45. A method for determining where at least one radio frequency transmitter is located with respect to a set range from a radio frequency receiver with each radio frequency transmitter periodically transmitting an identification code which identifies each radio frequency transmitter with a radio frequency carrier comprising:

producing a first function of a signal produced in response to each received radio frequency carrier transmitted with the identification code of one of the at least one radio frequency transmitter, producing a second function in response to at least one first function, comparing the second function to a value representing the set range and generating an alert when the comparison reveals that at least one of the at least one radio frequency transmitter is outside the set range.

46. A method in accordance with claim 45 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by each radio frequency transmitter; and

after generation of the alert using a directional antenna to receive transmissions of the identification code, transmitted with the radio frequency carrier, identifying the radio frequency transmitter from which the identification code was transmitted which caused the generation of the alert and in response to the radio frequency receiver being moved by a user the radio frequency receiver displaying in response to the second function a magnitude display to permit a user of the radio frequency receiver to locate a direction, from which a radio frequency carrier transmitted with the identification code of the radio frequency transmitter which generated the alert is received, producing a maximum magnitude display in response to the second function relative to the radio frequency receiver whereby a direction of the radio frequency transmitter which is outside of the set range is determined by the user of the radio frequency receiver relative to the radio frequency receiver.

47. A method in accordance with claim 46 wherein:

the second function is responsive to a plurality of the first functions.

48. A method in accordance with claim 45 further comprising:

using an omnidirectional antenna to receive the radio frequency carrier transmitted by one of the at least one radio frequency transmitter with the identification code of the one radio frequency transmitter and an alert which signals to a user of the radio frequency receiver that the user of the one radio frequency transmitter is transmitting a change in status of the user; and

in response to reception of the alert from one of the at least one radio frequency transmitter using a directional antenna to receive transmissions of the radio frequency carrier transmitted with the identification code identifying the radio frequency transmitter from which the alert was transmitted and in response to the radio frequency receiver being moved by a user the radio frequency receiver displaying, in response to the second function a magnitude display to permit a user of the radio frequency receiver to locate a direction, from which a radio frequency carrier with the identification code is received from the radio frequency transmitter which transmitted the alert, producing a maximum magnitude display in response to the second function relative to the radio frequency receiver whereby a direction of the radio frequency transmitter which transmitted the alert is determined by the user of the radio frequency receiver relative to the radio frequency receiver.

49. A method in accordance with claim 48 wherein:

the second function is responsive to a plurality of the first functions.

50. A method in accordance with claim 45 wherein:

the radio frequency carrier is modulated with a subcarrier; and

the subcarrier is modulated with at least one identification frame group, each identification frame group comprising a plurality of frames with at least one of the plurality of frames of the identification frame group containing bits encoding the identification code, a plurality of bits of error correction code in each frame, synchronization information for synchronizing a clock of the radio frequency receiver, and a command field for encoding the alert transmitted to the radio frequency receiver from the user of the radio frequency transmitter transmitting the alert.

51. A method in accordance with claim 50 wherein:

the subcarrier has cycles which are modulated with bits encoding the identification code with each cycle of the subcarrier being modulated with bits at a plurality of separated angular positions; and

for each received radio frequency carrier processing detected individual cycles of the subcarrier to calculate an integral of at least one selected modulated part of each of the individual cycles, numerically comparing each of the calculated integrals with a plurality of stored numerical ranges which ranges each represent one of a plurality of possible numerical values that the selected part may encode to identify a stored range numerically including the calculated integral, substituting for the at least one selected part of each of the cycles the one of the plurality of numerical values representative of the identified stored range including the calculated integral with each numerical value encoding one bit and decoding a plurality of bits.

52. A method in accordance with claim 51 wherein:

the second function is responsive to a plurality of the first functions.

53. A method in accordance with claim 50 wherein:

the second function is responsive to a plurality of the first functions.

54. A method in accordance with claim 45 wherein:

the second function is responsive to a plurality of the first functions.

55. A radio frequency receiver for determining where at least one radio frequency transmitter is located with respect to a set range from the radio frequency receiver with each radio frequency transmitter periodically transmitting an identification code which identifies each radio frequency transmitter with a radio common carrier comprising:

a processor, the processor producing a first function of a signal produced in response to each received radio frequency carrier transmitted with the identification code of one of the at least one radio frequency transmitter, producing a second function in response to at least one first function, comparing the second function to a numerical value representing the set range and generating an alert when a comparison reveals that at least one of the at least one radio frequency transmitter is outside the set range.

56. A radio frequency receiver in accordance with claim 55 further comprising:

an omnidirectional antenna, the omnidirectional antenna receiving the radio frequency carrier transmitted by each radio frequency transmitter; and

a directional antenna, the directional antenna after generation of the alert receives transmissions of the identification code, transmitted with the radio frequency carrier, identifying the radio frequency transmitter from which the identification code was transmitted which caused the radio frequency receiver to generate the alert and in response to the radio frequency receiver being moved by a user the processor in response to the second function controlling a magnitude display to permit a user of the radio frequency receiver to locate a direction, from which a radio frequency carrier transmitted with the identification code of the radio frequency transmitter generated the alert is received, producing a maximum magnitude display in response to the second function relative to the radio frequency receiver whereby a direction of the radio frequency transmitter which is outside of the set range is determined by the user of the radio frequency receiver relative to the radio frequency receiver.

57. A radio frequency receiver in accordance with claim 56 wherein:

the second function is responsive to a plurality of the first functions.

58. A radio frequency receiver in accordance with claim 55 further comprising:

an omnidirectional antenna, the omnidirectional antenna receiving the radio frequency carrier transmitted by one of the at least one radio frequency transmitter with the identification code of the one radio frequency transmitter and an alert which signals to a user of the radio frequency receiver that the user of the one radio frequency transmitter is transmitting a change in status of the user; and

a directional antenna, the directional antenna in response to reception of the alert from one of the at least one radio frequency transmitter receives transmissions of the radio frequency carrier transmitted with the identification code identifying the radio frequency transmitter from which the alert was transmitted and in response to the radio frequency receiver being moved by a user, the processor in response to the second function controlling a magnitude display to permit a user of the radio frequency receiver to locate a direction, from which a radio frequency carrier is received from the radio frequency transmitter transmitting the alert, producing a maximum magnitude display in response to the second function relative to the radio frequency receiver whereby a direction of the radio frequency transmitter which transmitted the alert is determined by the user of the radio frequency receiver relative to the radio frequency receiver.

59. A radio frequency receiver in accordance with claim 58 wherein:

the second function is responsive to a plurality of the first functions.

60. A radio frequency receiver in accordance with claim 55 wherein:

the radio frequency subcarrier is modulated with a subcarrier; and

the subcarrier is modulated with at least one identification frame group, each identification frame group comprising a plurality of frames with at least one of the plurality of frames of the identification frame group containing bits encoding the identification code, a plurality of bits of error correction code in each frame, synchronization information for synchronizing a clock of the radio frequency receiver, and a command field for encoding the alert transmitted to the radio frequency receiver from the user of the radio frequency transmitter transmitting the alert.

61. A radio frequency receiver in accordance with claim 60 wherein:

the second function is responsive to a plurality of the first functions.

62. A radio frequency receiver in accordance with claim 60 wherein:

the subcarrier has cycles which are modulated with bits encoding the identification code with each cycle of the subcarrier being modulated with bits at a plurality of separated angular positions; and

for each received radio frequency carrier, the processor processes detected individual cycles of the subcarrier to calculate an integral of at least one selected modulated part of each of the individual cycles, numerically compares each of the calculated integrals with a plurality of stored numerical ranges which ranges each represent one of a plurality of possible numerical values that the selected part may encode to identify a stored range numerically including the calculated integral, substitutes for the at least one selected part of each of the cycles the one of the plurality of numerical values representative of the identified stored range including the calculated integral with each numerical value encoding one bit and decodes a plurality of bits.

63. A radio frequency receiver in accordance with claim 62 wherein:

the second function is responsive to a plurality of the first functions.

64. A radio frequency receiver in accordance with claim 55 wherein:

the second function is responsive to a plurality of the first functions.

65. A method of use of at least one radio frequency transmitter with each radio frequency transmitter periodically transmitting an identification code which identifies each radio frequency transmitter with a radio frequency carrier comprising:

producing with a radio receiver a first function of a signal produced in response to reception of each radio frequency carrier transmitted with the identification code of one of the at least one radio frequency transmitter, producing a second function in response to at least one first function and in response to the second function either determining if one of the at least one radio frequency transmitter is outside of a set range between the one of the at least one radio frequency transmitter and the radio frequency receiver or determining a direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

66. A method in accordance with claim 65 wherein:

the radio frequency carrier is modulated with a subcarrier; and

the subcarrier is modulated with at least one identification frame group, each identification frame group comprising a plurality of frames with at least one of the plurality of frames of the identification frame group containing bits encoding the identification code, a plurality of bits of error correction code in each frame, synchronization information for synchronizing a clock of the radio frequency receiver, and a command field for encoding the alert transmitted to the radio frequency receiver from the user of the radio frequency transmitter transmitting the alert.

67. A method in accordance with claim 66 wherein:

the second function is responsive to a plurality of the first functions.

68. A method in accordance with claim 67 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

69. A method in accordance with claim 66 wherein:

the subcarrier has cycles which are modulated with bits encoding the identification code with each cycle of the subcarrier being modulated with bits at a plurality of separated angular positions; and

for each received radio frequency carrier processing detected individual cycles of the subcarrier to calculate an integral of at least one selected modulated part of each of the individual cycles, numerically comparing each of the calculated integrals with a plurality of stored numerical ranges which ranges each represent one of a plurality of possible numerical values that the selected part may encode to identify a stored range numerically including the calculated integral, substituting for the at least one selected part of each of the cycles the one of the plurality of numerical values representative of the identified stored range including the calculated integral with each numerical value encoding one bit and decoding a plurality of bits.

70. A method in accordance with claim 69 wherein:

the second function is responsive to a plurality of the first functions.

71. A method in accordance with claim 70 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

72. A method in accordance with claim 69 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

73. A method in accordance with claim 66 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

74. A method in accordance with claim 65 wherein:

the second function is responsive to a plurality of the first functions.

75. A method in accordance with claim 74 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

76. A method in accordance with claim 65 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

77. A radio frequency receiver for use with at least one radio frequency transmitter with each radio frequency transmitter periodically transmitting an identification code which identifies each radio frequency transmitter with a radio frequency carrier comprising:

a processor, the processor producing a first function of a signal produced in response to each received radio frequency carrier transmitted with the identification code of one of the at least one radio frequency transmitter, producing a second function in response to at least one first function, and in response to the second function either determining if one of the at least one radio frequency transmitter is outside of a set range between the one of the at least one radio frequency transmitter and the radio frequency receiver or determining a direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

78. A radio frequency receiver in accordance with claim 77 further comprising:

the radio frequency subcarrier is modulated with a subcarrier; and

the subcarrier is modulated with at least one identification frame group, each identification frame group comprising a plurality of frames with at least one of the plurality of frames of the identification frame group containing bits encoding the identification code, a plurality of bits of error correction code in each frame, synchronization information for synchronizing a clock of the radio frequency receiver, and a command field for encoding the alert transmitted to the radio frequency receiver from the user of the radio frequency transmitter transmitting the alert.

79. A radio frequency receiver in accordance with claim 78 wherein:

the subcarrier has cycles which are modulated with bits encoding the identification code of the radio frequency transmitter which transmitted the received radio frequency carrier with each cycle of the subcarrier being modulated with bits at a plurality of separated angular positions; and

for each received radio frequency carrier the processor processes detected individual cycles of the subcarrier to calculate an integral of at least one selected modulated part of each of the individual cycles, numerically compares each of the calculated integrals with a plurality of stored numerical ranges which ranges each represent one of a plurality of possible numerical values that the selected part may encode to identify a stored range numerically including the calculated integral, substitutes for the at least one selected part of each of the cycles the one of the plurality of numerical values representative of the identified stored range including the calculated integral with each numerical value encoding one bit and decodes a plurality of bits.

80. A radio frequency receiver in accordance with claim 79 wherein:

the second function is responsive to a plurality of the first functions.

81. A radio frequency receiver in accordance with claim 79 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

82. A radio frequency receiver in accordance with claim 80 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

83. A radio frequency receiver in accordance with claim 78 wherein:

the second function is responsive to a plurality of the first functions.

84. A radio frequency receiver in accordance with claim 83 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

85. A radio frequency receiver in accordance with claim 78 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

86. A radio frequency receiver in accordance with claim 77 wherein:

the second function is responsive to a plurality of the first functions.

87. A radio frequency receiver in accordance with claim 86 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

88. A radio frequency receiver in accordance with claim 77 wherein:

the receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one radio frequency transmitter relative to the radio frequency receiver.

89. A method of use of at least one frequency hopping radio frequency transmitter in radio communication with a synchronized frequency hopping radio frequency receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits with a radio frequency carrier which identifies each radio frequency transmitter to the frequency hopping radio frequency receiver comprising:

in response to receiving each radio frequency carrier determining if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, producing a first function of a signal produced in response to reception of each radio frequency carrier transmitted with at least part of the digits of identification code of one of the at least one frequency hopping radio frequency transmitter, producing a second function in response to at least one first function and in response to the second function either determining if one of the at least one frequency hopping radio frequency transmitter is outside of a set range between the one of the at least one frequency hopping radio frequency transmitter and the frequency hopping radio frequency receiver or determining a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

90. A method in accordance with claim 89 wherein:

the radio frequency carrier is modulated with a subcarrier; and

the subcarrier is modulated with at least one identification frame group, each identification frame group comprising a plurality of frames with at least one of the plurality of frames of the identification frame group containing bits encoding the identification code, a plurality of bits of error correction code in each frame, synchronization information for synchronizing a clock of the frequency hopping radio frequency receiver, and a command field for encoding the alert transmitted to the frequency hopping radio frequency receiver from the user of the frequency hopping radio frequency transmitter transmitting the alert.

91. A method in accordance with claim 90 wherein:

the subcarrier has cycles which are modulated with bits encoding the identification code with each cycle of the subcarrier being modulated with bits at a plurality of separated angular positions; and

for each received radio frequency carrier processing detected individual cycles of the subcarrier to calculate an integral of at least one selected modulated part of each of the individual cycles, numerically comparing each of the calculated integrals with a plurality of stored numerical ranges which ranges each represent one of a plurality of possible numerical values that the selected part may encode to identify a stored range numerically including the calculated integral, substituting for the at least one selected part of each of the cycles the one of the plurality of numerical values representative of the identified stored range including the calculated integral with each numerical value encoding one bit and decoding a plurality of bits.

92. A method in accordance with claim 91 wherein:

the second function is responsive to a plurality of the first functions.

93. A method in accordance with claim 91 wherein:

the frequency hopping radio receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

94. A method in accordance with claim 90 wherein:

the second function is responsive to a plurality of the first functions.

95. A method in accordance with claim 92 wherein:

the frequency hopping radio receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

96. A method in accordance with claim 94 wherein:

the frequency hopping radio receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

97. A method in accordance with claim 90 wherein:

the frequency hopping radio receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

98. A method in accordance with claim 89 wherein:

the second function is responsive to a plurality of the first functions.

99. A method in accordance with claim 98 wherein:

the frequency hopping radio receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

100. A method in accordance with claim 89 wherein:

the frequency hopping radio receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

101. A frequency hopping radio frequency receiver for use with at least one frequency hopping radio frequency transmitter synchronized by radio communication with the radio frequency frequency hopping receiver with each frequency hopping radio frequency transmitter periodically transmitting an identification code containing a plurality of digits with a radio frequency carrier which identifies each radio frequency transmitter to the frequency hopping radio frequency receiver comprising:

a processor, the processor in response to receiving each radio frequency carrier determines if at least part of the digits of the identification code of one of the at least one frequency hopping radio frequency transmitter is contained therein, produces a first function of a signal produced in response to each received radio frequency carrier transmitted with at least part of the digits of the identification code of one of the at least one radio frequency transmitter, produces a second function in response to at least one first function, and in response to the second function either determines if one of the at least one frequency hopping radio frequency transmitter is outside of a set range between the one of the at least one radio frequency transmitter and the frequency hopping radio frequency receiver or determines a direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

102. A frequency hopping radio frequency receiver in accordance with claim 101 further comprising:

the radio frequency subcarrier is modulated with a subcarrier; and

the subcarrier is modulated with at least one identification frame group, each identification frame group comprising a plurality of frames with at least one of the plurality of frames of the identification frame group containing bits encoding the identification code, a plurality of bits of error correction code in each frame, synchronization information for synchronizing a clock of the frequency hopping radio frequency receiver, and a command field for encoding the alert transmitted to the frequency hopping radio frequency receiver from the user of the frequency hopping radio frequency transmitter transmitting the alert.

103. A frequency hopping radio frequency receiver in accordance with claim 102 wherein:

the subcarrier has cycles which are modulated with bits encoding the identification code with each cycle of the subcarrier being modulated with bits at a plurality of separated angular positions; and

for each received radio frequency carrier, the processor processes detected individual cycles of the subcarrier to calculate an integral of at least one selected modulated part of each of the individual cycles, numerically compares each of the calculated integrals with a plurality of stored numerical ranges which ranges each represent one of a plurality of possible numerical values that the selected part may encode to identify a stored range numerically including the calculated integral, substitutes for the at least one selected part of each of the cycles the one of the plurality of numerical values representative of the identified stored range including the calculated integral with each numerical value encoding one bit and decodes a plurality of bits.

104. A frequency hopping radio frequency receiver in accordance with claim 103 wherein:

the second function is responsive to a plurality of the first functions.

105. A radio frequency receiver in accordance with claim 103 wherein:

the frequency hopping receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

106. A radio frequency receiver in accordance with claim 104 wherein:

the frequency hopping receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

107. A frequency hopping radio frequency receiver in accordance with claim 102 wherein:

the second function is responsive to a plurality of the first functions.

108. A radio frequency receiver in accordance with claim 107 wherein:

the frequency hopping receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

109. A radio frequency receiver in accordance with claim 102 wherein:

the frequency hopping receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

110. A frequency hopping radio frequency receiver in accordance with claim 101 wherein:

the second function is responsive to a plurality of the first functions.

111. A radio frequency receiver in accordance with claim 110 wherein:

the frequency hopping receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.

112. A frequency hopping radio frequency receiver in accordance with claim 101 wherein:

the frequency hopping receiver comprises an antenna providing selective omnidirectional and directional reception of the radio frequency carrier; and

the reception of the antenna is selectable so that omnidirectional reception is selected when a determination is made if one of the at least one frequency hopping radio frequency transmitter is outside of the set range and so that directional reception is selected when a determination is made of the direction of the one of the at least one frequency hopping radio frequency transmitter relative to the frequency hopping radio frequency receiver.