Signal absence detector

• US 4,419,765 A
• Filed: 07/01/1980
• Issued: 12/06/1983
• Est. Priority Date: 10/12/1979
• Status: Expired due to Term

• Current Assignee: Keith H. Wycoff
• Original Assignee: Keith H. Wycoff
• Inventors: Dittmer, William H., Wycoff, Keith H.
• Primary Examiner(s): Bookbinder, Marc E.
• Application Number:
  US06/165,212
• Time in Patent Office: 1,253 Days
• Field of Search: 455/32, 455/35, 455/36, 455/38, 455/161, 455/164, 455/165, 455/227, 455/228, 455/343, 455/266, 455/229, 328/138, 328/146, 328/149, 307/355, 307/356, 307/522, 307/524, 340/171 R, 340/171 A, 340/311.1, 340/825.44, 340/825.48, 340/825.71, 340/825.73, 340/825.74
• US Class Current: 340/7.35
• CPC Class Codes: H03G 3/005 Control by a pilot signal H03G3/001 takes precedence
• CPC Class Codes: H03G 3/344 Muting responsive to the amount of noise (noise squelch) H03G3/345 takes precedence
• CPC Class Codes: H03J 1/0091 provided with means for scanning over a band of frequencies H03J1/0058 takes precedence

Abstract

The signal absence detector controls an operator circuit which periodically provides an operator signal to render the processor circuit in a communication receiver operative. The absence detector responds to a processed signal which is not of a predetermined character to terminate the operator signal. In one form of the invention, the operator circuit is a battery saver which intermittently provides a supply voltage. When the incoming signal is of the predetermined character, the supply voltage continues. The absence detector terminates the supply voltage when it is determined that the incoming signal does not have that character. In another form of the invention, the absence detector is employed in a scanning receiver, in which case the operator circuit steps the receiver between the various channels. The receiver will remain tuned to a channel as long as the incoming signal may be of the predetermined character. As soon as determination is made that the incoming signal does not have such character, the receiver is stepped to the next channel.

Claims

1. In a receiver of a modulated incoming signal having a normally inoperative processor circuit that may be rendered operative to process an incoming signal and produce a processed signal including the modulation portion of the incoming signal, the combination comprising an operator circuit for periodically providing an operator signal to render the processor circuit operative to process the incoming signal, an absence detector having an input coupled to the processor circuit and having an output coupled to said operator circuit, said absence detector being responsive to any processed signal which is not of a predetermined character substantially immediately to terminate the operating signal, duration sensor means coupled to said absence detector for producing an output signal when absence of the processed signal of predetermined character is not detected in a first predetermined duration, and timer means coupled to said duration sensor means and being responsive to the start of the output signal to produce a timer signal persisting for a second predetermined duration, said operator circuit being coupled to said timer means and being responsive to the timer signal to extend the duration of the operator signal to the end of the second predetermined duration.

2. A signal detector for a selective call signal receiver having means for supplying AC signals, said detector comprising filter means having a fixed Q and being coupled to the supply means to allow passage of an AC signal, a source of a series of pulses spaced apart by an interval at least several times the duration of each such pulse, variable-voltage means coupled to said source and being responsive to each such pulse to produce a threshold voltage having a first value at the commencement of each pulse and varying during each pulse from the first value toward a second value, and comparator circuit means having first and second inputs respectively coupled to said filter means and said variable-voltage means, said comparator means being operative to produce a comparator signal for a duration related to the time the amplitude of an AC signal from said filter means is at least equal to the threshold voltage.

3. The signal detector of claim 2, and further comprising duration sensor means coupled to said comparator means for producing an output signal when the duration of the comparator signal exceeds a predetermined value.

4. The signal detector of claim 3, wherein said comparator means includes means for smoothing the comparator signal before application thereof to said duration sensor means.

5. The signal detector of claim 3, wherein said duration sensor means includes a charging circuit coupled to said comparator means for producing a charging voltage of varying magnitude, and an electronic switch circuit coupled to said charging circuit for producing the output signal when the magnitude of the charging voltage reaches a predetermined level.

6. The signal detector of claim 5, wherein said charging circuit includes a capacitor that is charged at a relatively slow rate in the presence of the comparator signal and is discharged at a relatively fast rate upon termination of the comparator signal.

7. The signal detector of claim 2, wherein said source is coupled to said comparator means and is responsive to the comparator signal to extend a pulse substantially to the end of the comparator signal.

8. The signal detector of claim 3, and further comprising timer means coupled to said duration sensor means and being responsive to the output signal to produce a timer signal persisting for a predetermined duration.

9. The signal detector of claim 8, wherein said source is coupled to said comparator means and is responsive to the comparator signal to extend a pulse substantially to the end of the comparator signal, and said source is coupled to said timer means and is responsive to the timer signal to extend a pulse substantially to the end of the timer signal.

10. A tone detector for a selective call signal receiver having means for supplying tones, said detector comprising normally operative filter means having a fixed Q and being coupled to the supply means to allow passage of a tone, a source of series of pulses, decay means coupled to said source and being responsive to each such pulse to produce a threshold voltage which decays from a first value toward a second value, comparator means having first and second inputs respectively coupled to said normally operative filter means and to said decay means, said comparator means being operative to produce a comparator signal for a duration related to the time the amplitude of a tone from said normally operative filter means is at least equal to the threshold voltage, duration sensor/timer means coupled to said comparator means and being responsive to the comparator signal having a duration exceeding a predetermined value to provide an enabling signal persisting for a given duration, and normally inoperative filter means having a fixed Q and being coupled to said supply means and to said timing means, said normally inoperative filter means being rendered operative by the enabling signal for the duration thereof to allow passage of a tone.

11. The signal detector of claim 10, wherein said source is coupled to said comparator means and is responsive to the comparator signal to extend a pulse substantially to the end of the comparator signal.

12. The signal detector of claim 11, wherein said source is coupled to said comparator means and is responsive to the comparator signal to extend a pulse substantially to the end of the comparator signal, and said source is coupled to said duration sensor/timer means and is responsive to the enabling signal to extend a pulse substantially to the end of the enabling signal.

13. A tone detector for a selective call signal receiver having means for supplying tones, said detector comprising normally operative filter means having a fixed Q and being coupled to the supply means to allow passage of a tone, a source of series of pulses, decay means coupled to said source and being responsive to each such pulse to produce a threshold voltage which decays from a first value toward a second value, first comparator means having first and second inputs respectively coupled to said normally operative filter means and to said decay means, said first comparator means being operative to produce a first comparator signal for a duration related to the time the amplitude of a tone from said normally operative filter means is at least equal to the threshold voltage, first duration sensor/timer means coupled to said first comparator means and being responsive to the first comparator signal having a duration exceeding a predetermined value to provide an enabling signal persisting for a given duration, normally inoperative filter means having a fixed Q and being coupled to said supply means and to said timer means, said normally inoperative filter means being rendered operative by the enabling signal for the duration thereof to allow passage of a second tone, second comparator means coupled to said normally inoperative filter means and being operative to produce a second comparator signal for a duration related to the time the amplitude of a second tone from said normally inoperative filter means exceeds a certain threshold voltage, and second duration sensor/timer means coupled to said second comparator means and being responsive to the second comparator signal exceeding a given value to provide a timer signal persisting for a certain duration.

14. The signal detector of claim 13, wherein said source is coupled to said first comparator means and is responsive to the first comparator signal to extend a pulse substantially to the end of the first comparator signal, said source is coupled to said first duration sensor/timer means and is responsive to the enabling signal to extend a pulse substantially to the end of the enabling signal, said source is coupled to said second comparator means and is responsive to the second comparator signal to extend a pulse substantially to the end of the second comparator signal, and said source is coupled to said second duration sensor/timer means and is responsive to the timer signal to extend a pulse substantially to the end of the timer signal.

15. In a selective call signal receiver including a processor circuit adapted to receive a carrier wave modulated by at least one code tone and to demodulate the code tone from the carrier wave, the combination comprising a resonant circuit coupled to the processor circuit for receiving the code tone, said resonant circuit including first reactance means, and second reactance means coupled together, said resonant circuit being resonant at a predetermined frequency, said second reactance means including amplifier means, and battery saver means for producing a pulsed supply voltage for at least the processor circuit and said resonant circuit so as cyclically to apply to and remove from the processor circuit and said resonant circuit the battery saver pulses, said battery saver means being connected to said amplifier means such that the voltage drop across said resonant circuit is substantially constant at substantially the same value both between battery saver pulses and during battery saver pulses, whereby said resonant circuit is precluded from ringing despite the cyclical application to and removal from said resonant circuit of the battery saver pulses.

16. In the filter of claim 15, wherein the voltage drop across said resonant circuit is kept at zero.

17. In the filter of claim 15, wherein said first reactance means is capacitor means and said second reactance means include further capacitor means.

18. In the filter of claim 15, and further comprising an operational amplifier having a signal input and a signal output, said first reactance means being coupled between said signal input and said signal output.

19. In the filter of claim 18, wherein said operational amp includes a bias input coupled to a source of pulsed bias voltage.

20. In the filter of claim 19, wherein said operational amp has a high supply terminal coupled to receive the pulsed supply voltage and a low supply terminal coupled to ground, and a high impedance coupled between the processor circuit and said signal input.

21. In a receiver of a modulated incoming signal having a normally inoperative processor circuit that may be rendered operative to process an incoming signal and produce a processed signal including the modulation portion of the incoming signal, the combination comprising a battery-saver circuit for periodically providing a supply voltage to render the processor circuit operative to process the incoming signal, an absence detector having an input coupled to the processor circuit and having an output coupled to said battery-saver circuit, said absence detector being responsive to any processed signal which is not of a predetermined character to substantially immediately terminate the supply voltage, duration sensor means coupled to said absence detector for producing an output signal when the processed signal has the predetermined character for a first predetermined duration, and timer means coupled to said duration sensor means and being responsive to the start of the output signal to produce a timer signal persisting for a second predetermined duration, said battery-saver circuit being coupled to said timer means and being responsive to the timer signal to extend the duration of the supply voltage to the end of the second predetermined duration.

22. In a selective-call communication receiver of an incoming signal modulated by a predetermined code and having a processor circuit that may be rendered operative to process an incoming signal and prduce a processed signal including the code, the combination comprising a battery-saver circuit for periodically providing a supply voltage to render the processor circuit operative to process the incoming signal, and an absence detector having an input coupled to the processor circuit and having an output coupled to said battery-saver circuit, said absence detector including means for detecting whether or not said processed signal includes the predetermined code and for terminating the supply voltage as soon as detection is made that said processed signal does not include said predetermined code.

23. In the receiver of claim 22, wherein said absence detector includes a frequency sensor having a variable bandwidth and having an output and a pulse input and having a signal input coupled to the processor circuit, said frequency sensor being operative to produce an output signal on said output in response to a processed signal having a frequency within a variable bandwidth, and a source of pulses coupled to said pulse input, said frequency sensor having means for causing the bandwidth to be relatively wide at the start of each pulse and to decrease during at least a portion thereof.

24. In the receiver of claim 22, wherein said operator circuit includes an astable multivibrator which is alternatively placed in two unstable conditions, said multivibrator producing the operator signal in one of the conditions thereof.

25. In the receiver of claim 22, wherein the predetermined code is followed by a voice message.

26. In the receiver of claim 22, wherein said absence detector includes filter means having a fixed Q and being coupled to the processor circuit to allow passage of the predetermined code, variable-voltage means coupled to said battery-saver circuit and being responsive to the supply voltage to produce a threshold voltage which varies from a first value to a second value, and comparator means having two inputs respectively coupled to said filter means and said variable-voltage means, said comparator means being operative to produce a comparator signal which persists for a duration related to the time the amplitude of the code from said filter means is at least equal to the threshold voltage, said battery-saver circuit including an astable multivibrator which is alternately placed in two conditions, said multivibrator being operative to produce the supply voltage in one of its conditions and alternately placed in the other condition for a predetermined duration, said multivibrator being coupled to said comparator means and remaining in the one condition for the duration of the comparator signal.

27. In the receiver of claim 22, wherein said absence detector includes filter means having a fixed Q and being coupled to the processor circuit to allow passage of the predetermined code, variable-voltage means coupled to said battery-saver circuit and being responsive to the supply voltage to produce a threshold voltage which varies from a first value to a second value, and comparator means having three inputs respectively coupled to said filter means and said variable-voltage means and said battery-saver circuit, said comparator means being responsive to the commencement of the supply voltage to commence producing a comparator signal which persists for a duration related to the time the amplitude of the code from said filter means is at least equal to the threshold voltage, said battery-saver circuit including a monostable multivibrator which is periodically placed in a stable condition to produce the supply voltage and is periodically placed in an unstable condition for a predetermined duration, said multivibrator being coupled to said comparator means and remaining in its stable condition for the duration of the comparator signal.

28. In a selective-call communication receiver of an incoming signal modulated by a predetermined tone and having a processor circuit that may be rendered operative to process an incoming signal and produce a signal including the tone, the combination comprising a battery-saver circuit for periodically providing a supply voltage to render the processor circuit operative to process the incoming signal, and an absence detector having an input coupled to the processor circuit and having an output coupled to said battery-saver circuit, said absence detector including means for detecting whether or not said processed signal includes the predetermined tone and for terminating the supply voltage as soon as detection is made that said processed signal does not include said predetermined tone.

29. In the receiver of claim 28, wherein said absence detector includes filter means having a fixed Q and being coupled to the processor circuit to allow passage of the processed signal, a source of series of pulses, variable-voltage means coupled to said source and being responsive to each such pulse to produce a threshold voltage which varies from a first value to a second value, and comparator means having first and second inputs respectively coupled to said filter means and said variable-voltage means, said comparator means being operative to produce a comparator signal for a duration related to the time the amplitude of the process signal passing through said filter means is at least equal to the threshold voltage.

30. In a selective-call communication receiver of an incoming signal modulated by a predetermined sequence of tones and having a processor circuit that may be rendered operative to process an incoming signal and produce a processed signal including the predetermined sequence of tones, the combination comprising a battery-saver circuit for periodically providing a supply voltage to render the processor circuit operative to process the incoming signal, and an absence detector having an input coupled to the processor circuit and having an output coupled to said battery-saver circuit, said absence detector including means for detecting whether or not said processed signal includes the predetermined sequence of tones and for terminating the supply voltage as soon as detection is made that said processed signal does not include any of the tones in said predetermined sequence.

31. In a scanning receiver for receiving a modulated incoming signal in one of a plurality of channels and having a processor circuit which includes signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, mixer means for mixing the modulated incoming signal with the local signal, and demodulator means coupled to the mixer means for supplying a processed signal including the modulation portion of the incoming signal, the combination comprising an absence detector including means for detecting whether or not said processed signal has a predetermined character and for producing a start signal as soon as detection is made that said processed signal does not have said predetermined character, and stepping means having an input and at least two outputs and being operative to produce output signals on said outputs respectively having variable durations dependent on the occurrence of a start signal applied to the input of said stepping means, said signal generating means being coupled to the outputs of said stepping means, said stepping means being responsive to each start signal substantially immediately to change the frequency of the local signal to correspond to the next channel to be scanned.

32. In a scanning receiver for receiving a modulated incoming signal in one of a plurality of channels and having a processor circuit which includes signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, mixer means for mixing the modulated incoming signal with the local signal, and demodulator means coupled to the mixer means for supplying a processed signal including the modulation portion of the incoming signal, the combination comprising an absence detector including means responsive to the processed signal not having a predetermined character to produce a start signal, stepping means responsive to each start signal substantially immediately to change the frequency of the local signal to correspond to the next channel to be scanned, duration sensor means coupled to said absence detector for producing an output signal when the processed signal has the predetermined character for a first predetermined duration, and timer means coupled to said duration sensor means and being responsive to the start of the output signal to produce a timer signal persisting for a second predetermined duration, said stepping means being coupled to said timer means and being responsive to the timer signal to prevent stepping to the end of the second predetermined duration.

33. In a scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by a predetermined code, the receiver having a processor circuit which includes signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, mixer means for mixing the modulated incoming signal with the local signal, and demodulator means coupled to the mixer means for supplying a processed signal including the modulation portion of the incoming signal, the combination comprising an absence detector including means for detecting whether or not said processed signal includes a predetermined code and for producing a start signal as soon as detection is made that said processed signal does not include said predetermined code, and stepping means having an input and at least two outputs and being operative to produce output signals on said outputs respectively having variable durations dependent on the occurrence of a start signal applied to the input of said stepping means, said signal generating means being coupled to the outputs of said stepping means, said stepping means being responsive to each start signal substantially immediately to change the frequency of the local signal to correspond to the next channel to be scanned.

34. In the scanning receiver of claim 33, wherein the predetermined code is a single tone.

35. In the scanning receiver of claim 34, the combination further comprising battery-saver circuit for supplying to the processor circuit a supply voltage during operation of said stepping means for rendering the processor circuit operative to process the incoming signal, said battery-saver circuit being responsive to a start signal corresponding to the last channel to be scanned to discontinue for a fixed duration supplying the supply voltage to the processor circuit.

36. In the scanning receiver of claim 35, wherein said battery-saver circuit includes an astable multivibrator which is alternately placed in two conditions, said multivibrator being operative to produce a supply voltage in one of its conditions and is alternately placed in the other condition for a predetermined duration, said multivibrator being coupled to said absence detector and remaining in the one condition until a start signal is produced corresonding to the last channel to be scanned.

37. In a scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by a predetermined sequence of tones, the receiver having a processor circuit which includes signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, mixer means for mixing the modulated incoming signal with the local signals, and demodulator means coupled to the mixer means for supplying a processed signal including the modulation portion of the incoming signal, the combination comprising an absence detector including means for detecting whether or not said processed signal includes the predetermined sequence of tones and for producing a start signal as soon as detection is made that said processed signal does not include any one of the tones in said predetermined sequence, and stepping means having an input and at least two outputs and being operative to produce output signals on said outputs respectively having variable durations dependent on the occurrence of a start signal applied to the input of said stepping means, said signal generating means being coupled to the outputs of said stepping means, said stepping means being responsive to each start signal substantially immediately to change the frequency of the local signal to correspond to the next channel to be scanned.

38. In the scanning receiver of claim 37, the combination further comprising a battery-saver circuit for supplying to the processor circuit a supply voltage during operation of said stepping means for rendering the processor circuit operative to process the incoming signal, said battery-saver circuit being responsive to a start signal corresponding to the last channel to be scanned to discontinue for a fixed duration supplying the supply voltage to the processor circuit.

39. In the receiver of claim 38, wherein said absence detector includes filter means having a fixed Q on each frequency and being coupled to the processor circuit to allow passage of the predetermined sequence of tones in the proper sequence, variable-voltage means coupled to said battery-saver circuit and being responsive to the supply voltage to produce a threshold voltage which varies during each tone from a first value to a second value, and comparator means having three inputs respectively coupled to said filter means and said variable-voltage means and said battery-saver circuit, said comparator means being responsive to the commencement of the supply voltage to commence producing a comparator signal which persists for a duration related to the time the amplitude of each tone from said filter means is at least equal to the threshold voltage, said battery-saver circuit including a monostable multivibrator which is periodically placed in one condition to produce the supply voltage and is periodically placed in a second condition for a predetermined duration, said multivibrator being coupled to said comparator means and remaining in its stable condition for the duration of the comparator signal.

40. In the receiver of claim 38, wherein said absence detector includes filter means having a fixed Q on each frequency and being coupled to the processor circuit to allow passage of the predetermined sequence of tones in the proper sequence, variable-voltage means coupled to said battery-saver circuit and being responsive to the supply voltage to produce a threshold voltage which varies during each tone from a first value to a second value, and comparator means having two inputs respectively coupled to said filter means and said variable-voltage means, said comparator means being operative to produce a comparator signal which persists for a duration related to the time the amplitude of each tone from said filter means is at least equal to the threshold voltage, said battery-saver circuit including an astable multivibrator which is alternately placed in stable conditions, said multivibrator being operative to produce the supply voltage in one of its conditions and is alternately placed in the other condition for a predetermined duration, said multivibrator being coupled to said comparator means and remaining in the one condition for the duration of the comparator signal.

41. In a scanning receiver for receiving a modulated incoming signal in one of a plurality of channels and having a normally inoperative processor circuit which includes signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, mixer means for mixing the modulated incoming signal with the local signal, and demodulator means coupled to the mixer means for supplying a processed signal including the modulation portion of the incoming signal, the combination comprising an absence detector including means for detecting whether or not said processed signal has a predetermined character and for producing a start signal as soon as detection is made that said processed signal does not having said predetermined character, stepping means having an input and at least two outputs and being operative to produce output signals on said outputs respectively having variable durations dependent on the occurrence of a start signal applied to the input of said stepping means, said signal generating means being coupled to the outputs of said stepping means, said stepping means being responsive to each start signal substantially immediately to change the frequency of the local signal to correspond to the next channel to be scanned, and a battery-saver circuit for supplying to the processor circuit a supply voltage during operation of said stepping means for rendering the processor circuit operative to process the incoming signal, said battery-saver circuit being coupled to the outputs of said stepping means and being responsive to a start signal corresponding to the last channel to be scanned to discontinue for a fixed duration supplying the supply voltage to the processor circuit.

42. In a scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by a predetermined code, the receiver having a normally inoperative processor circuit which includes signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, mixer means for mixing the modulated incoming signal with the local signal, and demodulator means coupled to the mixer means for supplying a processed signal including the modulation portion of the incoming signal, the combination comprising an absence detector including means for detecting whether or not said processed signal includes a predetermined code and for producing a start signal as soon as detection is made that said processed signal does not include said predetermined code, stepping means having an input and at least two outputs and being operative to produce output signals on said outputs respectively having variable durations dependent on the occurrence of a start signal applied to the input of said stepping means, said signal generating means being coupled to the outputs of said stepping means, said stepping means being responsive to each start signal substantially immediately to change the frequency of the local signal to correspond to the next channel to be scanned, and a battery-saver circuit for supplying to the processor circuit a supply voltage during operation of said stepping means for rendering the processor circuit operative to process the incoming signal, said battery-saver circuit being coupled to the outputs of said stepping means and being responsive to the start signal corresponding to the last of the frequency-determining means to discontinue for a fixed duration supplying the supply voltage to the processor circuit.

43. In the scanning receiver of claim 42, wherein said absence detector includes filter means having a fixed Q on any frequency searched for and being coupled to the processor circuit to allow passage of the predetermined code, variable-voltage means coupled to said battery-saver circuit and being responsive to the supply voltage to produce a threshold voltage which varies from a first value to a second value, and comparator means having two inputs respectively coupled to said filter means and said variable-voltage means, said comparator means being operative to produce a comparator signal which persists for a duration related to the time the amplitude of the code from said filter means is at least equal to the threshold voltage, said battery-saver circuit including an astable multivibrator which is alternately placed in two conditions, said multivibrator being operative to produce the supply voltage in one of its conditions and alternately placed in the other condition for a predetermined duration, said multivibrator being coupled to said comparator means and remaining in the one condition for the duration of the comparator signal.

44. In the scanning receiver of claim 42, wherein said absence detector includes filter means having a fixed Q on any searched for frequency and being coupled to the processor circuit to allow passage of the predetermined code, variable-voltage means coupled to said battery-saver circuit and being responsive to the supply voltage to produce a threshold voltage which varies from a first value to a second value, and comparator means having three inputs respectively coupled to said filter means and said variable-voltage means and said battery-saver circuit;

said comparator means being responsive to the commencement of the supply voltage to commence producing a comparator signal which persists for a duration related to the time the amplitude of the code from said filter means is at least equal to the threshold voltage, said battery-saver circuit including a monostable multivibrator which is periodically placed in a stable condition to produce the supply voltage and is periodically placed in an unstable condition for a predetermined duration, said multivibrator being coupled to said comparator means and remaining in its stable condition for the duration of the comparator signal.

45. In a selective-call scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by a predetermined sequence of tones, the combination comprising signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, stepping means for cyclically changing the frequency of the local signal, mixer means coupled to said signal generating means for mixing the modulated incoming signal with the local signal, demodulator means coupled to said mixer means for supplying the modulation components of the incoming signal, frequency responsive means coupled to said demodulator means and being sequentially responsive to each tone to allow passage thereof, and circuit means coupled to said frequency-responsive means for producing a start signal as soon as detection is made by said frequency-responsive means that the incoming signal does not include any one of the tones in the predetermined sequence of tones, and stepping means having an input and at least two outputs and being operative to produce output signals on said outputs respectively having variable durations dependent on the occurrence of a start signal applied to the input of said stepping means, said signal generating means being coupled to the outputs of said stepping means, said stepping means being coupled to said circuit means and being responsive to each start signal to change the frequency of the local signal.

46. In the selective call scanning receiver of claim 45, wherein the local signal has two frequencies corresponding to two channels.

47. In the selective call scanning receiver of claim 45, wherein said stepping means includes a counter.

48. In the selective call scanning receiver of claim 45, wherein said frequency-responsive means includes a single filter and a plurality of frequency-determining means individually connectable to said filter to cause said filter to have one of a corresponding plurality of center tone frequencies, and further stepping means for connecting said frequency-determining elements in circuit with said filter means as the tones are received in sequence.

49. In a selective-call scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by modulation components including a predetermined tone, the combination comprising a signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, stepping means for cyclically changing the frequency of the local signal, mixer means coupled to said signal generating means for mixing the modulated incoming signal with the local signal, demodulator means coupled to said mixer means for supplying the modulation components of the incoming signal, frequency-responsive means coupled to said demodulator means for producing a filter signal having a maximum amplitude when the incoming signal includes the predetermined tone, a source of a series of pulses, variable-voltage means coupled to said source and being responsive to each such pulse to produce a threshold voltage which varies from a first value to a second value, the comparator means having first and second inputs respectively coupled to said frequency-responsive means and said variable-voltage means, said comparator means being operative to produce a comparator signal for a duration related to the time the amplitude of the filter signal is at least equal to the threshold voltage, said stepping means being coupled to said comparator means and being responsive to termination of the comparator signal to change the frequency of the local signal.

50. In the selective-call scanning receiver of claim 49, and further comprising reset means coupled from said stepping means and to said variable-voltage means and being responsive to the changing of the frequency of the local signal to reset said variable-voltage means.

51. In the selective-call scanning receiver of claim 50, wherein said reset means is also coupled from said stepping means to said frequency-responsive means and is responsive to the connection of said frequency-determining means to reset said frequency-responsive means.

52. In a selective-call scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by a predetermined sequence of tones, the combination comprising signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, stepping means for cyclically changing the frequency of the local signal, mixer means coupled to said signal generating means for mixing the modulated incoming signal with the local signal, demodulator means coupled to said mixer means for supplying the modulation components of the incoming signal, frequency responsive means coupled to said demodulator means and being sequentially responsive to each tone for producing a sequence of filter signals each having a maximum amplitude when the incoming signal includes the tone to which said frequency-responsive means is then tuned, a source of a series of pulses, variable-voltage means coupled to said source and being responsive to each such pulse to produce a threshold voltage which varies from a first value to a second value, and comparator means having first and second inputs respectively coupled to said frequency-responsive means and said variable-voltage means, said comparator means being operative to produce comparator signals each for a duration related to the time the amplitude of the corresponding filter signal is at least equal to the threshold voltage, said stepping means being coupled to said comparator means and being responsive to termination of the comparator signal to change the frequency of the local signal.

53. In the selective-call scanning receiver of claim 52, and further comprising reset means coupled from said stepping means and to said variable-voltage means and being responsive to the changing of the frequency of the local signal to reset said variable-voltage means.

54. In the selective-call scanning receiver of claim 52, wherein the local signal has two frequencies.

55. In the selective-call scanning receiver of claim 52, and further comprising battery saver means for producing a pulsed supply voltage for at least a portion of said receiver, said stepping means being coupled to said battery saver means and being operative in the presence of a comparator signal to cause the supply voltage to become continuous.

56. In a selective-call scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by a predetermined sequence of tones, the combination comprising signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, stepping means for cyclically changing the frequency of the local signal, mixer means coupled to said signal generating means for mixing the modulated incoming signal with the local signal, demodulator means coupled to said mixer means for supplying the modulation components of the incoming signal, frequency-responsive means coupled to said demodulator means and being sequentially responsive to each tone for producing a sequence of filter signals each having a maximum amplitude when the incoming signal includes the tone to which said frequency-responsive means is then tuned, a source of a series of pulses, variable-voltage means coupled to said source and being responsive to each such pulse to produce a threshold voltage which varies from a first value to a second value, comparator means having first and second inputs respectively coupled to said frequency-responsive means and said variable-voltage means, said comparator means being operative to produce comparator signals each for a duration related to the time the amplitude of the corresponding filter signal is at least equal to the threshold voltage, said stepping means being coupled to said comparator means and being responsive to termination of the comparator signal to change the frequency of the local signal, and timer means coupled to said comparator means and being responsive to the output signal to produce a timer signal persisting for a predetermined duration, said stepping means being further coupled to said timer means and being responsive to the timer signal to preclude changing the frequency of the local signal for the duration of timer signal.

57. In the selective-call scanning receiver of claim 56, wherein said frequency-responsive means includes a single filter and a plurality of frequency-determining means individually connectable to said filter to cause said filter to have one of a corresponding plurality of center tone frequencies, further stepping means for connecting said frequency-determining elements in circuit with said filter means as the tones are received in sequence, and duration sensor means coupled to said comparator means for producing an output signal upon termination of the tone if the duration of the comparator signal exceeds a predetermined value to cause said further stepping means to connect the next frequency-determining element in circuit.

58. In a selective-call scanning receiver for receiving an incoming signal in one of a plurality of channels, which incoming signal is modulated by a predetermined sequence of tones, the combination comprising battery saver means for producing a pulsed supply voltage for at least a portion of the receiver, signal generating means operative to produce a local signal having one of a corresponding plurality of frequencies, stepping means for cyclically changing the frequency of the local signal and for operating said battery saver means, mixer means coupled to said signal generating means for mixing the modulated incoming signal with the local signal, demodulator means coupled to said mixer means for supplying the modulation components of the incoming signal, frequency-responsive means coupled to said demodulator means and being sequentially responsive to each tone to allow passage thereof, and circuit means coupled to said frequency-responsive means and being responsive to absence of each tone therefrom for producing a start signal, said stepping means being coupled to said circuit means and being responsive to each start signal to change the frequency of the local signal and to cause the supply voltage to become continuous.

59. In the selective-call scanning receiver of claim 58, wherein said stepping means is constructed and arranged to cause the local signal to have each of said plurality of frequencies for a duration equal to the inverse of said plurality times the duration of a pulse of supply voltage, whereby during each pulse of supply voltage the local signal will have each of the plurality of frequencies.