RU2099870C1 - Detection of microphone with radio transmitter and device for its implementation - Google Patents

Abstract

FIELD: radio engineering, detection of microphone with transmitter installed without authorization in limited space. SUBSTANCE: proposed process includes radiation of acoustic signal, reception of radio frequency signals, demodulation and filtration of signals. Radio frequency signals are received beyond limits of limited space in two points of limited space as minimum and are processed by Fourier transform comparing intensities of spectral components for each radio frequency. Those signals which have bigger or equal intensities in two points of limited space in comparison with intensities of spectral components of radio signal beyond limits of limited space are extracted. Then radio signals with specified spectral components are received, acoustic signal has duration ΔT, demodulated signals within interval ΔT are processed by Fourier transform at least twice. Device for implementation of detection has former of acoustic signal and radio receiver composed of mixer, discriminator, indicator connected with outputs to inputs in series and local oscillator. Device is supplemented with two antennas, antenna commutator, analog-to-digital converter, unit of on-line storages, Fourier transform unit, threshold unit, unit of comparators, on-line storage, code converter, electronic controlled switch, control unit. Local oscillator is manufactured in the form of digital synthesizer and indicator displays spectral components. EFFECT: enhanced reliability of detection. 8 cl, 14 dwg

Description

 The invention relates to radio engineering and can be used to detect unauthorized installed in a limited space microphone with a radio transmitter, the so-called "radio bug".

 A known time delay spectrometer containing an acoustic signal shaper and a receiver configured to measure the spectral characteristics of an acoustic signal reflected from an object (US Pat. No. 3,4666,652, CL 343-14, published 09.09.69).

 This device is not intended to detect a hidden microphone with a radio transmitter.

 The closest technical solution for the claimed are the method and device described in US patent N 3939420, H 04 B 1/46, publ. 02/17/76.

 A known method for detecting a microphone with a radio transmitter that is unauthorized installed in a limited space includes emitting an acoustic signal into a limited space, receiving radio frequency signals generated by a radio transmitter and modulated by an acoustic signal in a limited space, demodulating and filtering them, and judging by a demodulated filtered signal about the presence of a radio transmitter microphone.

 A known device for detecting a microphone with a radio transmitter includes an acoustic signal shaper and a radio receiver made of an antenna, mixer, intermediate frequency amplifier, discriminator, indicator connected by outputs to the inputs in series, and a local oscillator connected by the output to the second input of the mixer.

 The known method and device have the following limitations: low speed, since the entire range of radio frequencies is subjected to demodulation, insufficient detection quality, since it is possible to detect only simple radio frequency signals with amplitude and frequency modulation, it is impossible to recognize the “radio bug” signals whose radio frequency coincides with the frequency broadcasting stations and various radio interference.

 The problem solved by the invention, improving the quality of detection.

 The technical result for the method of improving performance and making it possible to detect the installed "radio bug" in the conditions of radio interference, making it possible to detect an unauthorized microphone with a radio transmitter using any kind of modulation with a time-varying frequency parameter.

 The technical result that can be obtained for the device during its implementation, improving the reliability of detection and speed with the possible action of various radio interference, including from broadcasting stations; providing the ability to process a radio frequency signal with AM, narrow FM, wide FM modulation; with frequency scrambling; with signal inversion, for example, single-lane, single-lane side; signals, tunable according to a certain law, unchanged in time, the so-called "frequency mosaic".

 To solve the problem with the achievement of the specified technical result, in the known method of detecting a microphone with a radio transmitter, unauthorized installed in a limited space, including radiation in a limited space of an acoustic signal, receiving in a limited space of radio frequency signals generated by a radio transmitter and modulated by an acoustic signal, their demodulation and filtering , judgment on the demodulated filtered signal of the presence of a microphone broadcast According to the invention, the radio frequency signals are preliminarily received outside the limited space and at least two points of the limited space and processed by Fourier transform, the intensity of the spectral components corresponding to the radio frequency signals at two points of the limited space is compared for each radio frequency, and the spectral components with the maximum intensity relative to each other and relative to the level of false alarm, compare for each radio hour the spectral components with the maximum intensity obtained for the radio frequency signal for two points of a limited space, with the spectral components of the radio frequency signal outside the limited space relative to each other and the level of false alarm, finally distinguish those that for two points of a limited space have a greater or equal intensity in comparing with the intensity of the spectral components of the radio frequency signal outside a limited space, then receive only those radio frequency signals that correspond to the finally selected spectral components, the acoustic signal is emitted with a duration of ΔT, the demodulated signals in the interval ΔT are processed by the Fourier transform at least twice, and while maintaining the frequency position of the spectral components of the demodulated signal in the interval ΔT and their absence Outside of this interval, a microphone is judged.

There are additional options for implementing the method, in which it is advisable that:
an acoustic signal would be emitted at least two times at different frequencies:
the emitted acoustic signal would be generated with at least one additional frequency, and the demodulated signal was processed by Fourier transform with such a frequency resolution that the spectral components of the frequencies of the emitted acoustic signal would coincide in frequency;
emitted acoustic signals separately in time from at least three points of limited space, and at a known distance of these points relative to each other, the location of the microphone with the radio transmitter was judged by the time delay of arrival of the demodulated signal relative to the emitted acoustic signal.

 To solve the problem with achieving the specified technical result in a known device for detecting a microphone with a radio transmitter containing an acoustic signal shaper and a radio receiver made of an antenna, mixer, intermediate frequency amplifier, discriminator, indicator connected by outputs to inputs in series, and a local oscillator connected to the output at least one antenna and an antenna switch are introduced to the second input of the mixer according to the invention, and the antennas are connected to to the mixer through the antenna switch, an analog-to-digital converter, a random access memory unit, a Fourier transform unit, a threshold device connected in series with the data outputs and inputs are introduced, and the discriminator output is connected to the indicator input through them, the local oscillator is made in the form of a digital frequency synthesizer and introduced a comparator unit, random access memory, a code converter connected in series with the data outputs and inputs, and a threshold device data output connected n, with the data input of the digital frequency synthesizer through them, an electronic controlled switch is inserted, and the output of the intermediate frequency amplifier is connected to the discriminator input through the first output of the electronic controlled switch, and the second output of the electronic controlled switch is connected to the input of the analog-to-digital converter, the control unit the outputs of which are connected to the control inputs of the antenna switch, analog-to-digital Converter, block random access memory devices Fourier transform unit, threshold device, comparator unit, random access memory, code converter, digital frequency synthesizer, acoustic signal shaper, and the indicator is configured to indicate spectral components.

Additional embodiments of the device are possible, in which it is advisable that:
the shaper of the acoustic signal was made of a low-frequency generator and loudspeaker with the ability to change the frequency of the acoustic signal;
the acoustic signal generator was made of a low-frequency generator and a loudspeaker, while the low-frequency generator would be capable of simultaneously generating at least two frequencies, the frequency interval between which was selected from the condition that their spectral components coincide in the Fourier transform unit;
the acoustic signal shaper was made of a low-frequency generator and at least three loudspeakers connected by inputs to the output of the low-frequency generator with the possibility of spacing the loudspeakers relative to each other and a time indicator and an acoustic signal arrival delay measuring unit were introduced, connected by its input to the output of the acoustic signal discriminator, and the output to the time indicator input, while the control unit one of the control outputs was connected to the control the input of the unit for measuring the delay in the arrival of an acoustic signal.

 These advantages, as well as features of the present invention will become apparent when considering the best option for its implementation with reference to the accompanying figures.

In FIG. 1 shows a functional diagram of a device; in FIG. 2 is a spectral diagram at the output of a Fourier transform block for a first antenna located in a limited space; in FIG. 3 is the same as FIG. 2 for a second antenna located in a confined space; in FIG. 4 is a spectral diagram for the first and second antennas at the output of the comparator unit; in FIG. 5 is a spectral diagram for a third reference antenna placed outside a limited space; in FIG. 6 is a spectral diagram at the output of the final allocation comparator unit as a result of comparing the signals for the first and second antennas with the signal for the third antenna; in FIG. 7 is a spectral diagram of an emitted acoustic signal; in FIG. 8 is a spectral diagram of a demodulated signal in the absence of scrambling; in FIG. 9 is the same as FIG. 8 in the presence of scrambling; in FIG. 10 frequency-time diagram of the emitted acoustic signal; in FIG. 11 - two spectrograms at the output of the Fourier transform block; in FIG. 12
time-frequency diagram of the emitted acoustic signal with time division at two separate frequencies with two closely spaced frequencies; in FIG. 13 four spectrograms at the output of the Fourier transform block; in FIG. 14 appearance in projection on the floor plan when determining the location of the microphone with a radio transmitter.

 Since the method of detecting a microphone with a transmitter is implemented during the operation of the device, it will be described in the section describing its operation.

 The device (Fig. 1) for detecting a microphone with a radio transmitter comprises an acoustic signal generator 1 made of a low-frequency generator 2 and at least one loudspeaker (Fig. 1 shows three loudspeakers 3, 4, 5) and a radio receiver 6. The radio receiver 6 is made of antenna 7, mixer 8, amplifier 9 of intermediate frequency, discriminator 10, indicator 11, connected by outputs to inputs in series, and local oscillator 12, connected by output to second input of mixer 8.

 At least one antenna has been introduced (Fig. 1 shows two additional antennas: an antenna 13, which is installed in a limited space and a reference antenna 14, which is installed outside a limited space) and an antenna switch 15. Antennas 7, 13, 14 are connected to the input of the mixer 8 through the antenna switch 15. An analog-to-digital converter 16, an operative storage unit 17, a Fourier transform unit 18, a threshold device 19, connected in series with the outputs and inputs, are introduced. The output of the discriminator 10 is connected to the input of the indicator II through an analog-to-digital converter 16, a block 17 of random access memory, a block 18 of the Fourier transform, the threshold device 19.

 The local oscillator 12 is made in the form of a digital frequency synthesizer. A comparator unit 20, a random access memory 21, a code converter 22, connected in series with the outputs and inputs, are introduced. The data output of the threshold device 19 is connected to the data input of the local oscillator-digital frequency synthesizer 12 through the comparator unit 20, random access memory 21, code converter 22.

 An electronic controlled switch 23 is introduced, and the output of the intermediate frequency amplifier 9 is connected to the input of the discriminator 10 through the first output of the electronic controlled switch 23, and the second output of the electronic controlled switch 23 is connected to the input of the analog-to-digital converter 16. A control unit 24 is introduced, the control outputs of which are connected with the control inputs of the antenna switch 15, analog-to-digital Converter 16, block 17 random access memory, block 18 Fourier transform, the threshold troystva 19, block comparator 20, a random access memory 21, code converter 22, a digital frequency synthesizer 12, the low-frequency generator 2 generator 1 of the acoustic signal. The indicator 11 is configured to indicate spectral components.

 The acoustic signal generator 1 may be capable of changing the frequency of the acoustic signal, for example, with the possibility of the low-frequency generator 2 operating at separate frequencies.

 In another additional embodiment, the driver 1 may be made of a low-frequency generator 2, for example, based on a frequency synthesizer, with the possibility of simultaneously generating at least two frequencies, the frequency interval between which is selected from the condition that their spectral components coincide in the Fourier transform unit 18.

 In order to provide reception and transmission at different points in space, antennas 7, 11, 13 can be connected by a high-frequency cable to the antenna switch 15, and loudspeakers 3, 4, 5 are connected by wires to the outputs of the low-frequency generator 2. A time indicator 25 and a block 26 are introduced measuring the delay in the arrival of an acoustic signal, connected by its input to the output of the discriminator 10, and by the output to the input of the indicator 25. The control unit 24 of one of the control outputs is connected to the control input of the unit 25.

 In FIG. 1 also shows a “radio bug” made with a microphone 27 and a radio transmitter 28.

 The device operates as follows.

 A variant is possible in which the radio receiver 6 is moved outside the studied limited space, for example, the premises or the passenger compartment of the vehicle, in this case it is sufficient to use two antennas, for example, 7 and 13, on one of which all radio frequency signals outside the limited space are memorization. In this case, the radio load of the studied range is first recorded, and then the antennas 7 and 13 are brought into a limited space and new radio frequency signals are detected.

 In another embodiment, one of the antennas, such as antenna 14, is carried out of a limited space, and registration of the radio load of the range and detection of new radio frequency signals is performed simultaneously.

 Since the radio-frequency signals of broadcasting stations are attenuated by the boundaries of a limited space, in order to accelerate the detection of the "radio bug" in both the first and second versions, the broadcasting signals and time-constant radio noise are screened out.

 The device can also be implemented in the analogue version, however, to expedite processing, it is advisable to use fast Fourier transform by digitally processing the signals under study.

 Pre-receive radio frequency signals outside the limited space of the antenna 13 and at least two points of the limited space by the antennas 7 and 13. Since the radio frequency picture in a limited space has nodes in which the radio frequency signals can have different intensities, the use of several antennas, for example 7 and 13, improves detection reliability. The more antennas are used, the higher the quality of detection.

 Received radio frequency signals separately in time by controlling the unit 24 of the antenna switch 15 are processed by the mixer 8, amplifier 9. The control unit 24 serves to temporarily synchronize the operation of the remaining units, in particular to generate clock signals for digital devices. In the recording mode of the radio range loading, an electronic controlled switch 23 connects the output of the amplifier 9 to the input of the analog-to-digital converter 16, bypassing the discriminator 10. Next, the signals are converted to digital form and fed to block 17, which contains as many random access memory devices as the antennas are used. At the output of block 18, the spectral components (Fig. 2, 3) of the corresponding RF signals in a digital code are obtained.

 The threshold device serves to set the threshold value corresponding to the level of false alarm, due to which the spectral components of radio noise are eliminated. The value of the selected threshold depends on the practically existing radio environment, as well as on various parameters of the limited space, for example, such as the radio-absorbability of the walls of the room or the vehicle body.

 In block 20 of the comparators, the intensities of the spectral components corresponding to the radio frequency signals at two points of a limited space are compared for each radio frequency, and the spectral components with maximum intensity relative to each other and relative to the threshold are selected (Fig. 4).

 Next, in block 20, for each radio frequency, the spectral components with the maximum intensity obtained for the radio frequency signal from the antennas 7, 13 are compared with the spectral components of the radio frequency signal outside the limited space from the antenna 14 (Fig. 5) with respect to each other and the threshold level. The time algorithm for the operation of blocks 18, 19, 20, and 21 is controlled by block 24 and finally select those components that for two points in a limited space have a greater or equal intensity in comparison with the intensity of the spectral components of the radio frequency signal outside the limited space (Fig. 6). Digital codes of such components are recorded in random access memory 21.

 Only those radio frequency signals are received that correspond to the finally allocated spectral components, for which the signals are converted to the corresponding codes in the code converter 22 and fed to the digital frequency synthesizer 12. The digital frequency synthesizer 12 supplies signals to the mixer 8 only with a frequency that corresponds to passing through the mixer 8 signals detected in block 20 of the comparators.

 Thus, in contrast to the known method and device, not all radio frequency signals are subjected to further demodulation, but previously detected, with the formation of a list of probable radio frequency signals, which are then subjected to demodulation, which allows a hundred times increase detection speed.

 For demodulation, an electronic controlled switch 23 connects the output of amplifier 9 to the input of discriminator 10, which can be made frequency and / or amplitude. To work with the acoustic signal, the clock frequency of the block 24 is changed and it is chosen lower, while the block 20 is turned off, and the data from the threshold device 19 are sent to the indicator 11.

 Shaper 1 emit an acoustic signal of duration ΔT (Fig. 7). The signals demodulated by discriminator 10 are processed by block 18 at least two times in the interval ΔT (Fig. 10-13), i.e. during the existence of an acoustic signal, it is filtered several times by means of the Fourier transform. Such processing can significantly increase the reliability of detection of the microphone 27 with the radio transmitter 28.

 While maintaining the frequency position of the spectral components of the demodulated signal (Fig. 8-13) in the interval ΔT and their absence outside this interval, the presence of a microphone 27 is judged.

 Since in the proposed technical solution, the criterion for maintaining the frequency position of the spectral components of the demodulated signal is selected as the detection criterion, the method allows for the detection of a microphone 27 with a radio transmitter 28 with almost all types of modulation of the radio frequency signal (Fig. 8, 9): with frequency scrambling, with inversion a signal, for example, a single-lane, single-lane side; signals, tunable according to a certain law, unchanged in time, the so-called "frequency mosaic".

 To further improve the quality of detection, an acoustic signal can be radiated at least twice at different frequencies (Figs. 12, 13), while the criterion for maintaining the frequency position remains valid for each individual frequency.

 In addition, the studies showed that the reliability of the detection is significantly increased if a radiated acoustic signal is generated with at least one additional frequency (Fig. 12), and the demodulated signal is processed by block 18 with such a frequency resolution that the spectral components of the main and additional frequencies the emitted acoustic signal coincided in frequency. In this case, the additional frequency is chosen very close to the main one and the acoustic signal is emitted simultaneously at these frequencies. In the general case, there can be more than two such frequencies.

 With the current level of technology, the method allows for detection with high speed.

 The analysis time of the 15 MHz wide range with a resolution of 8 kHz and 0.5 dB in level is 1 s, which allows for 5 minutes to analyze the frequency range from 30 to 2000 MHz for the presence of a "radio bug".

 To detect the location of the microphone 27 with the radio transmitter 28, it is possible to use methods of measuring distance by the time delay of the acoustic signal, see, for example, US patent N 3566348, G 01 S 11/00, publ. 02/23/71 or application of Great Britain N 2170907, G 01 S 11/00, publ. 08/13/86. However, these methods do not allow to identify the location of the "radio bug".

 To identify the location of the microphone with the transmitter, it is advisable to emit acoustic signals separately in time from at least three points of limited space, and for a known distance of these points relative to each other, judge the location of the microphone 27 with the radio transmitter 28 by the time delay of the arrival of the demodulated signal relative to the emitted acoustic signal.

 To detect the location of the "radio bug", a time indicator 25 and an acoustic signal arrival delay measuring unit 26 are connected to the radio receiver 6 and connected to the output of the discriminator 10 by its input and to the output of the indicator 25.

 By the control signal from block 24, the low-frequency generator 2 is started and block 26 is simultaneously started. By the time delay of the signal, the location of the radio bug can be determined, the propagation speed of the radio frequency signal can be neglected, since it practically does not affect the accuracy of determining the location. The appearance of the location calculation is shown in FIG. 14. In the general case, it is necessary to have four loudspeakers in order to obtain only one point of intersection of the four spheres with the measured radius. However, when placing loudspeakers 3, 4, 5, for example, in the corner of the room, it is enough to have three of them, since the second intersection point will be outside the limited space.

 The most successfully claimed method of detecting a microphone with a radio transmitter and device can be used by various consumers to combat unauthorized listening to rooms. The method and device allows to detect the presence of active embedded devices of the following types: radio microphones, microphones with the transmission of information over the power grid, telephone radio transmitters, radio stethoscopes.

Claims (8)

 1. A method of detecting a microphone with a radio transmitter that is unauthorized installed in a limited space, including emitting an acoustic signal into a limited space, receiving radio frequency signals generated by a radio transmitter and modulated by an acoustic signal in a limited space, demodulating and filtering them, narrowing by a demodulated filtered signal about the presence of a radio transmitter microphone characterized in that the pre-receive radio frequency signals outside the boundaries space and at least two points in a limited space and process them with the Fourier transform, compare for each radio frequency the intensity of the spectral components corresponding to radio frequency signals at two points in a limited space, and select the spectral components with maximum intensity relative to each other and relative to the level of false alarm, for each radio frequency, the spectral components with maximum intensity obtained for the radio frequency are compared the needle for two points of a limited space, with the spectral components of the RF signal outside the limited space relative to each other and the level of false alarm, finally select those that for two points of a limited space have a greater or equal intensity of the spectral components of the radio frequency signal than outside the limited space, then only those radio frequency signals are received that correspond to the finally allocated spectral components them, an acoustic signal is emitted with a duration of ΔT, filtering is carried out by means of the Fourier transform at least twice in the interval ΔT, and while maintaining the frequency position of the spectral components of the demodulated signal in the interval ΔT and their absence outside this interval, the presence of a microphone is judged.  2. The method according to claim 1, characterized in that the acoustic signal is emitted at least two times at different frequencies.  3. The method according to claim 1, characterized in that the emitted acoustic signal is generated with at least one additional frequency, the Fourier transform is carried out with such a frequency resolution that the spectral components of the frequencies of the emitted acoustic signal coincide in frequency.  4. The method according to claim 1, characterized in that additional acoustic signals are emitted separately in time from at least three points of limited space, and at a known distance of these points relative to each other, the location of the microphone with the radio transmitter is judged by the time delay of arrival of the demodulated signal relative to the emitted acoustic signal.  5. A device for detecting a microphone with a radio transmitter, comprising an acoustic signal conditioner and a radio receiver comprising an antenna, a mixer and an intermediate frequency amplifier connected in series, a discriminator, an indicator and a local oscillator, the output of which is connected to the second input of the mixer, characterized in that at least one additional antenna, antenna switch, serially connected analog-to-digital converter, random access memory unit, Fourier transform unit, burner device, comparator unit, random access memory, code converter, the output of which is connected to the input of the local oscillator, made in the form of a digital frequency synthesizer, an electronic controlled switch, the input of which is connected to the output of the intermediate frequency amplifier, the first output with the discriminator input, the second output with the input of the analog-to-digital converter, a control unit whose control outputs are connected to the control inputs of the antenna switch, analog-to-digital converter, block random access memory, Fourier transform unit, threshold device, comparator unit, random access memory, code converter, digital frequency synthesizer, acoustic signal conditioner, threshold device output is connected to the indicator input, antennas are connected to the mixer input through an antenna switch, the indicator is made with the possibility indication of spectral components.  6. The device according to claim 5, characterized in that the shaper of the acoustic signal is made of a low-frequency generator and loudspeaker with the ability to change the frequency of the acoustic signal.  7. The device according to claim 5, characterized in that the acoustic signal conditioner is made of a low-frequency generator and a loudspeaker, while the low-frequency generator is capable of simultaneously generating at least two frequencies, the frequency interval between which is selected from the condition of coincidence and their spectral components with Fourier transform block.  8. The device according to claim 5, characterized in that the shaper of the acoustic signal is made of a low-frequency generator and at least three loudspeakers connected to the output of the low-frequency generator with the possibility of spacing the loudspeakers relative to each other and a time indicator and a unit for measuring the delay of arrival of the acoustic signal are introduced, the input of which is connected to the discriminator output, the output with the time indicator input, and the control input with the control output of the control unit.

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