CELLULAR TELEPHONE DISABLING DEVICE

Abstract: The invention provides a method of disabling operation of a cellular telephone in a particular zone. The method includes sweeping an interference signal across a frequency band in which the cellular telephone operates to inhibit communication between the celluar telephone and a base station. The invention also provides a cellular telephone disabling device for disabling a cellular telephone in a particular zone.

Description: CELLULAR TELEPHONE DISABLING DEVICE THIS INVENTION relates to cellular telephone communication. In particular it relates to a method of disabling operation of a cellular telephone in a particular zone and to a cellular telephone disabling device. In accordance with the invention, there is provided a method of disabling operation of a cellular telephone in a particular zone, the method including sweeping an interference signal across a frequency band in which the cellular telephone operates to inhibit communication between the cellular telephone and a base station. The method may include generating a source signal; sweeping the source signal across the frequency band in which the cellular telephone operates to provide the interference signal; and transmitting the interference signal in the zone thereby to disable operation of the telephone. The source signal generated may be a monotone source signal. Typically, in South Africa, the frequency band across which the interference signal is swept is the GSM band of about 935 MHz to about 960 MHz. CONFIRMATION COPT Further in accordance with the invention, there is provided a cellular telephone disabling device for disabling a cellular telephone in a particular zone, the device including a signal source for generating a source signal; control means for sweeping the source signal across a frequency band in which the cellular telephone operates to provide an interference signal; and transmitter means operable to transmit the interference signal in the zone thereby to disable operation of the telephone. The signal source may include conventional circuitry to generate a monotone source signal. Preferably the signal source includes temperature compensation means for compensating for the effect of ambient temperature changes on the signal source. The signal source may be a voltage controlled oscillator (VCO). The control means may be operable to provide a voltage control signal to which the VCO is responsive. The control means may include circuitry for generating a sweep control signal, and an adjustable voltage reference for setting a centre frequency of the voltage controlled oscillator. Typically, the circuitry is oscillator circuitry and the sweep control signal is a sawtooth waveform. The control means may include a summing circuit to sum the sweep control signal and the voltage reference. The sweep control signal typically has a frequency of about 20 KHz so that the interference signal sweeps across the frequency band in which the cellular telephone operates at a frequency of about 20 KHz. The device may include an amplifier for amplifying the interference signal prior to transmission thereof. The amplifier may be a conventional amplifier, e.g an HMPX 3002 or the like, adjusted to have a gain of about 30 dB. The device may further include a bandpass filter connected intermediate the VCO and the amplifier. The bandpass filter typically operates in the range of about 935 MHz to about 960 MHz. The device may include a low-pass filter, e.g. a conventional LC filter, connected to an output of the amplifier for attenuating harmonics of the interference signal. Typically, the low-pass filter has a cutoff frequency of about 1 GHz. The invention is now described, by way of example, with reference to the accompanying diagrammatic drawings. In the drawings, Figure 1 shows a schematic block diagram of a cellular telephone disabling device in accordance with the invention; and Figure 2 shows a circuit diagram of the device of Figure 1 . Referring to the drawings, reference numeral 10 generally indicates a cellular telephone disabling device for disabling communication between a cellular telephone in a particular zone and a base station. The device 1 0 includes a signal source in the form of a voltage controlled oscillator (VCO) 14, a controller 1 6 connected to the VCO 14 and operable to sweep a source signal of the VCO 14 across a frequency band in which the cellular telephone operates. The VCO 14 provides an interference signal which is fed into a bandpass filter 1 8. The device 10 further includes transmitter circuitry 20 comprising an amplifier 22, a low-pass filter 24, and an antenna (not shown). The signal source is a conventional voltage controlled oscillator 14 and the controller 1 6 is operable in a conventional fashion to provide an output voltage control signal which is fed into the VCO 14 thereby to control the interference signal generated at its output. Accordingly, the controller 1 6 includes an adjustable voltage reference 26 which defines a centre frequency of the VCO 14, oscillator circuitry 28 for generating a sweep control signal in the form of a sawtooth wave, and a summing circuit 30. The summing circuit 30 sums the output voltage control signal and the output voltage of the voltage reference 26. An output of the summing circuit 30, which is fed into the voltage controlled oscillator 14 defines a sweep control signal with a frequency of about 20 KHz thereby to sweep the interference signal through the frequency band in which the cellular telephone operates. The frequency band is typically about 935 MHz to about 960 MHz. In order to filter out any unwanted frequencies in the event of the voltage controlled oscillator 14 being faulty, the bandpass filter 1 8 with an operating range of about 935 MHz to about 960 MHz filters the interference signal generated by the voltage controlled oscillator 14 prior to it being fed into the amplifier 22. The amplifier 22 is typically a conventional amplifier e.g an HMPX 3002 or the like, adjusted by circuitry 32 to have a gain of about 30 dB. An output of the amplifier 22 is fed into the low-pass filter 24 which typically has a cut off frequency of about 1 GHz. The power output from the output of the low-pass filter 24 is typically about 20 dBm. However, it is to be appreciated that, dependant upon the size of the zone in which cellular telephones are to be disabled, the power output may be adjusted accordingly by means of the circuitry 32. Further, in various countries or regions throughout the world, the frequency band in which the device 10 operates may vary. Referring in particular to Figure 2 of the drawings, the oscillator circuitry 28 for generating the sweep control signal includes conventional oscillator circuitry employing operational amplifiers 34, 36 to generate a sawtooth waveform which is fed along line 38 to gain control circuitry 40. The sweep control signal is then fed via line 42 to the summing circuit 30. The adjustable voltage reference 26 has its output voltage reference adjusted by a variable resistor 44 and fed via line 46 to the summing circuit 30. The voltage controlled oscillator 14 includes conventional circuitry and generates the interference signal which is then fed along line 50 into the amplifier 22. An output interference signal, the power of which is determined by the variable resistor 32, is fed via the low-pass filter 20 to an antenna system (not shown) which is arranged to have an appropriate radiation pattern dependant upon the application of the device 10. The low-pass filter 20 typically has a cutoff frequency of about 1 GHz. In certain embodiments of the invention (not shown) the voltage controlled oscillator 14 includes temperature compensation means for compensating for deviations in the interference signal due to ambient temperature changes. In use, the device 10 is mounted in a particular zone for example a bank or the like where disabling of operation of cellular telephones is required. In order for a cellular telephone to effect communication between a base station, control information in the form of digital data received by the cellular telephone must be error free. The interference signal in the form of a single tone which is scanned across the operating frequency band introduces errors in the signal received by the cellular telephone thereby disabling the communication between the cellular telephone and the base station. The Applicant believes that as the interference signal is a single tone which is scanned across the cellular telephone frequency band, energy transmitted by the device 10 is confined to a single receive channel thereby effectively to disable operation of a cellular telephone in the selected zone. Thus, the blocking of cellular communication is achieved with lower output power from the device 10 than would be required if a broad band noise-like jamming signal was to be generated to disable cellular telephone communication. The Applicant further believes that by confining the sweep range to the intended blocking band, and if it is swept at a slow enough rate, an additional advantage of reduced incidental blocking of the adjacent frequency spectrum is obtained.

Claims: CLAIMS 1 . A method of disabling operation of a cellular telephone in a particular zone, the method including sweeping an interference signal across a frequency band in which the cellular telephone operates to inhibit communication between the cellular telephone and a base station. 2. A method as claimed in Claim 1 , which includes generating a source signal; sweeping the source signal across the frequency band in which the cellular telephone operates to provide the interference signal; and transmitting the interference signal in the zone thereby to disable operation of the telephone. 3. A method as claimed in Claim 2, in which the source signal generated is a monotone source signal. 4. A method as claimed in any one of the preceding claims 1 to 3 inclusive, in which the frequency band across which the interference signal is swept is the GSM band of about 935 MHz to about 960 MHz. 5. A cellular telephone disabling device for disabling a cellular telephone in a particular zone, the device including a signal source for generating a source signal; control means for sweeping the source signal across a frequency band in which the cellular telephone operates to provide an interference signal; and transmitter means operable to transmit the interference signal in the zone thereby to disable operation of the telephone. 6. A device as claim in Claim 5, in which the signal source includes conventional circuitry to generate a monotone source signal. 7. A device as claimed in Claim 5 or Claim 6, in which the signal source includes temperature compensation means for compensating for the effect of ambient temperature changes on the signal source. 8. A device as claimed in any one of the preceding claims 5 to 7 inclusive, in which the signal source is a voltage controlled oscillator. 9. A device as claimed in Claim 8, in which the control means is operable to provide a voltage control signal to which the voltage controlled oscillator is responsive. 1 0. A device as claimed in any one of the preceding claims 5 to 9 inclusive, in which the control means includes circuitry for generating a sweep control signal and an adjustable voltage reference for setting a centre frequency of the voltage controlled oscillator. 1 1 . A device as claimed in Claim 10, in which the circuitry is oscillator circuitry and the sweep control signal is a sawtooth waveform. 1 2. A device as claimed in Claim 10 or Claim 1 1 , in which the control means includes a summing circuit to sum the sweep control signal and the voltage reference. 13. A device as claimed in any one of the preceding claims 10 to 1 2 inclusive, in which the sweep control signal has a frequency of about 20 KHz so that the interference signal sweeps across the frequency band in which the cellular telephone operates at a frequency of about 20 KHz. 14. A device as claimed in any one of the preceding claims 5 to 1 3 inclusive, which includes an amplifier for amplifying the interference signal prior to transmission thereof. 1 5. A device as claimed in Claim 14, in which the amplifier is a conventional amplifier, adjusted to have a gain of about 30 dB. 1 6. A device as claimed in Claim 14 or Claim 1 5, which includes a bandpass filter connected intermediate the voltage controlled oscillator and the amplifier. 1 7. A device as claimed in Claim 1 6, in which the bandpass filter operates in the range of about 935 MHz to about 960 MHz. 1 8. A device as claimed in any one of the preceding claims 14 to 1 7 inclusive, which includes a low-pass filter, connected to an output of the amplifier for attenuating harmonics of the interference signal. 1 9. A device as claimed in Claim 18, in which the low-pass filter has a cutoff frequency of about 1 GHz. 20. A method as claimed in Claim 1 , substantially as herein described and illustrated. 21 . A device as claimed in Claim 5, substantially as herein described and illustrated. 22. A new method or a new device, substantially as herein described.

Inventors: SCHMITZ MATTHIAS MARIA ALFRED, STANDER PIERRE, SCHMITZ, MATTHIAS, MARIA, ALFRED, STANDER, PIERRE
Applicants: SCHMITZ MATTHIAS MARIA ALFRED, STANDER PIERRE, WHITE HENDRIK CHRISTOFFEL, SCHMITZ, MATTHIAS, MARIA, ALFRED, STANDER, PIERRE, WHITE, HENDRIK, CHRISTOFFEL
Application year: 1999
Main classification: H04K3
IPC codes: H04W48