RU2123767C1 - Electroacoustic transducer - Google Patents

Abstract

FIELD: electrical engineering; electric telephone communications; acoustic control of locations. SUBSTANCE: transducer that has filter connected in series with two-wire communication line connected to microphone-effect load and high-frequency oscillator whose input is connected to first wire of two-wire communication line is provided, in addition, with series-connected low-frequency band amplifier, low-frequency filter, detector, band filter. Input of band filter is connected to second wire of two-wire communication line. Output of low-frequency band amplifier functions as transducer output. EFFECT: improved sensitivity of device. 7 dwg

Description

 The invention relates to the field of radio engineering, in particular to telephone communications technology, and can be used for acoustic monitoring of premises.

 Known devices, for example: "Interactive telephone alerting device" according to the application of Great Britain N 2251765, published in the Journal of Abstracts (RJ), ser. 29A, 1992, N 5, ref. N, 497P; "Remote-controlled equipment for assessing the condition of telephone lines conducting direct current" according to US patent N 5115462, published in the Russian Federation, ser. 29A, 1993, N 11, ref. 360P; "Device for checking the connection to the telephone switchboard" according to the Swedish patent N 501021, published in the Russian Federation, ser. 29A, 1995, N 9, ref. N 440P.

 In these devices, the tasks of alerting and checking the telephone line are solved. These devices can be considered analogues of the claimed device.

 However, in these devices, audio signals are transmitted through the communication line to the telephone and returned. This is sufficient only for monitoring the subscriber line, but this does not allow for acoustic monitoring of the premises.

 Closest in its technical essence to the claimed one is "The device of the RF-imposition on the telephone," described in the book of V.I. Yarochkina "Security of information systems", M., Axis-89, 1996, pp. 104-105, Fig. 2.40, which is selected as a prototype.

 The prototype consists of a filter included in the rupture of a two-wire line connected to a load with a microphone effect (telephone) and an RF generator, the output of which is connected to a two-wire communication line between the filter and a load with a microphone effect.

 A feature of the prototype in comparison with these analogues is the presence in its composition of a filter and an RF generator, based on which the problem of electro-acoustic conversion can be solved.

 The disadvantage of the prototype is the low sensitivity due to the fact that the received signal is radiated by a load having a microphone effect, in particular a telephone, with a relatively low level of electromagnetic radiation.

 The aim of the invention is to develop a device for electro-acoustic conversion, providing higher sensitivity.

 This goal is achieved by the fact that in a known device containing a filter included in the gap of a two-wire communication line connected to a load having a microphone effect, and an RF generator, the output of which is connected to the first wire of a two-wire communication line, an additional band-pass low-frequency amplifier is introduced, low-pass filter, detector, band-pass filter, the input of which is connected to the second wire of a two-wire communication line, the grounding output of the high-frequency generator is connected to the grounding input of the low-frequency band the amplifier and the grounding input of the detector, and the input of the low-frequency bandpass amplifier through a low-pass filter is connected to the output of the detector, the signal input of which is connected to the output of the bandpass filter.

 The listed new set of essential features provides an increase in the sensitivity of the device by replacing the radio channel with a matched filtering device and isolating a low-frequency signal from a two-wire communication line.

 The analysis of the prior art made it possible to establish that analogues that are characterized by a combination of features that are identical to all the features of the claimed technical solution are absent, which indicates the compliance of the claimed invention with the condition of patentability "novelty".

 The search results for known solutions in this and related fields of technology in order to identify features that match the distinctive features of the claimed object from the prototype showed that they do not follow explicitly from the prior art. The prior art also did not reveal the popularity of the impact provided by the essential features of the claimed invention transformations to achieve the specified technical result. Therefore, the claimed invention meets the condition of patentability "inventive step".

 The claimed device is illustrated by the drawing in FIG. one; in FIG. 2 is a timing diagram explaining the principle of operation of the device.

 The electro-acoustic conversion device shown in FIG. 1 consists of a filter 1, an RF generator 2, a low-pass band amplifier 3, a low-pass filter 4, a detector 5, a band-pass filter 6, a two-wire communication line 7, a first wire 8, a second wire 9, and a load 10 having a microphone effect. The filter 1 is included in the gap of the two-wire communication line 7. The two-wire communication line 7 is connected to a load 10 having a microphone effect. The output of the RF generator 2 is connected to the first wire 8 of the two-wire communication line 7. The grounding output of the RF generator 2 is connected to the grounding input of the strip low-frequency amplifier 3 and the grounding input of the detector 5. The signal input of the strip low-frequency amplifier 3 through a low-pass filter 4 is connected to the output of the detector 5. The signal input of the detector 5 through a band-pass filter 6 is connected to the second wire 9 of the two-wire communication line 7. The output of the bandpass low-frequency amplifier 3 is the output of the device.

 The filter 1 is designed to prevent the penetration of the signal from the RF generator towards the communication line. The filter must pass low-frequency signals in a two-wire communication line and delay the high-frequency signal with a frequency of 150 ... 200 kHz, creating a resistance of 5 ... 10 kOhm in the indicated frequency range. It can be made, for example, in the form of two chokes. The calculation of such chokes is known and is given in the reference literature, for example, in the radio amateur manual, R. M. Tereshchuk, K. M. Tereshchuk, S. A. Sedov, “Semiconductor receiving and amplifying devices”, K., Naukova Dumka, 1982, p. 111-151.

 The high-frequency generator 2 is designed to generate an RF signal and feed it through the first wire 8 relative to the earth in the direction of the load 10. Such generators with a frequency of 150 ... 200 kHz are known, are widely used in electrical engineering and are commercially available from the industry, for example, GZ-36 generators, GZ-103, etc.

 Striped bass amplifier 3 is designed to amplify the selected low-frequency signal. The band-woofer amplifier at the central frequency of 1 ... 1.5 kHz should have a selectivity of 40 dB / octave and a sensitivity of at least 3 μV. These requirements are met, for example, by UNIPAN selective nanovoltmeters type 233 or 238 manufactured by Poland.

 The low-pass filter 4 is designed to isolate the low-frequency signal and suppress high-frequency noise coming from the output of the detector 6. The low-pass filter should have a cutoff frequency of about 3 kHz. The construction of filters with such parameters is known. In particular, it can be implemented on RC elements; the calculation of such a filter is given there on page 434.

 The detector 5 is designed to detect the amplitude-modulated signal from the load 10 through the second wire 9 of the two-wire communication line. Such a detector is known; its calculation is given there on page 470.

 The band-pass filter 6 provides the allocation of the modulated RF signal. The band-pass filter at a frequency of 150 ... 200 kHz should have a passband of about 6 kHz and can be made in the form of a coordinated sequential LC circuit, the calculation of which is given in the book by B.P. Aseev "Oscillating chains", M., Svyazizdat, 1955 , pp. 49-61.

 The claimed device operates as follows.

 High-frequency oscillations from the RF generator 2 (timing diagram 1 in Fig. 2) are fed through the first wire 8 to the load 10. When using the telephone apparatus as a load, the RF oscillations arrive at its elements through an open contact group even when the telephone is on-hook. Through the action of an acoustic (speech) signal on the load elements, 10 RF oscillations are modulated by speech. Filter 1 prevents the RF signal from entering the communication line and prevents the dissipation of its power in the line circuits of the telephone exchange. From the second wire 9, the mixture of the modulated RF signal and the noise signal of the telephone line (timing diagram 3, FIG. 2) is fed to the input of a bandpass filter 6 tuned to the resonant frequency of the RF signal. Thanks to the use of a band-pass filter 6, the modulated signal is filtered out from the noise of the two-wire communication line (timing diagram 4 in Fig. 2). In the detector 5, a low-frequency speech signal is emitted, which, after being filtered by a low-pass filter 4 (timing diagram 5 in Fig. 2), is amplified by a low-frequency strip amplifier 3 and is output to the device (timing diagram 6 in Fig. 2).

 This ensures a high level of the signal at the output of the strip low-frequency amplifier 3 and increases the sensitivity of the electro-acoustic conversion device and, therefore, the desired result is achieved.

 The ability to achieve the specified technical result was tested on a device layout in which a telephone was used as a load, filter 1 and a band-pass filter 6 were made using 5 mH inductors wound around ring ferrite cores with an external diameter of 35 mm. The GZ-36 generator was used as the high-frequency generator 2, and the UNIPAN type 238 was used as the low-frequency band amplifier 3. The detector 5 was made on a D-220 diode, and the low-pass filter 4 was a single-link filter on standard RC elements. Structurally, the device is made in the form of a rectangular block with dimensions of 150x70x40 mm.

 The experiments conducted with the prototype showed that the proposed device can detect allocated low-frequency signals at a distance 10 times greater compared to the prototype.

Claims (1)

 An electro-acoustic conversion device containing a high-frequency generator, the output of which is connected to the first wire of a two-wire communication line to supply a high-frequency signal to the load side, which has a microphone effect and is connected to a two-wire communication line, and a filter designed to prevent the signal from the high-frequency generator from penetrating towards the communication line and included in the gap of a two-wire communication line, characterized in that a low-frequency strip amplifier is introduced, the filter is low x frequency, detector, bandpass filter, the input of which is connected to the second wire of the two-wire communication line, the grounding output of the high-frequency generator is connected to the grounding input of the strip low-frequency amplifier and the grounding input of the detector, and the signal input of the low-frequency amplifier through the low-pass filter is connected to the output of the detector, the signal the input of which is connected to the output of the bandpass filter, and the output of the bandpass low-frequency amplifier is the output of the device.

Images