RU2011298C1 - Device for suppression of noise level in communication equipment - Google Patents

Abstract

FIELD: communication equipment. SUBSTANCE: device for suppression of noise level in communication equipment has operational amplifier 1, half-section of low-pass filter 2, phase shifter 3 and voltage divider 4. The device for suppression of noise level in communication equipment, along with the functions of noise suppression and gain of legitimate signal, fulfils the function of gain correction required for elimination of frequency distortions introduced by the communication line. EFFECT: facilitated procedure. 1 dwg

Description

 The invention relates to communication technology, and more specifically to communication devices in rail transport, in which interference is observed induced by the contact electric traction network, and there is a need to suppress interference.

 Known devices for compensatory reduction of the level of said interference. A feature of the known devices is the inclusion of communication equipment at the input (outside it), and the achieved interference suppression (achieved signal-to-noise ratio) at the input of the communication equipment remains the same at its output, since in a communication equipment a linear amplifier undesirably amplifies both useful signals and and interference.

 The purpose of the invention is to increase the signal-to-noise ratio at the output of communication equipment.

 The drawing shows a structural electrical diagram of the proposed device.

 A device for reducing the level of interference in communication equipment contains an operational amplifier (OA) 1, a half-link low-pass filter (LPF) 2, a phase shifter 3, a voltage divider 4 containing a resistor 5 and a variable resistor 6. A resistor 7 is included in the inverse input circuit of the OS 1, and in the negative feedback circuit of the op-amp - resistor 8.

 The device is included in the communication equipment instead of a linear amplifier of the receiving path of the equipment and operates as follows.

 The input terminals of the device receive useful signals and interfering voltages from the communication line. As is known, the largest disturbing voltages induced by the electric traction contact network have frequencies of 50, 100, 150, 200 Hz. In the device, these voltages from the input terminals are supplied to both inputs of the OS 1 (inverse and direct) by two separate circuits. The interfering voltages pass through the resistor 7 to the inverse input, and the other way through the direct input through the filter D-0.4 2 separating them, transformer phase shifter 3, and voltage divider 4.

 When passing through the half-link of the low-pass filter 2, the interfering voltages receive a phase shift, but with their further passage through the phase shifter 3, which rotates the phase by another 180 ° (with the corresponding inclusion of its windings), the interfering voltages acquire the initial phase. The interference voltages supplied to the inverse input of the op-amp 1 through the resistor 7 are not subjected to phase changes. As a result, interfering voltages are supplied to both op amp inputs in the same phase (in phase). They are also equal in magnitude by changing the resistance of the variable resistor 6 in the voltage divider 4.

 When both op-amp 1 inputs have equal and in-phase interfering voltages, as follows from the op amp theory, they are suppressed as much as possible and are detected at the output of op-amp 1 by attenuated 40-50 dB.

 It is necessary to take into account that voltage equalization at the op amp inputs in this case is achieved only at one frequency of interfering voltages transmitted by the low-pass filter of the low-pass filter 2, since the filter introduces attenuation into the circuit, which varies depending on the frequency. It is advisable to equalize at the inputs of the OS 1 and obtain the maximum suppression of a more significant interfering voltage observed at a frequency of 50 Hz.

 Since with increasing filter attenuation with increasing frequency the inequality of the values of interfering voltages at the inputs of OS 1 increases, with the maximum suppression of the interference voltage with a frequency of 50 Hz, interference voltages of higher frequencies of 100, 150, 200 Hz are suppressed less.

 To reduce this dependence of the suppression of noise from changes in the filter attenuation in the passband, the device provides for a decrease in the steepness of the filter attenuation with increasing frequency, achieved by the fact that the device has not an integer value, but a half-coupled low pass filter 2. This is achieved by expanding the passband with 0.2 to 0.4 kHz and the fact that the phase shifter 3 has a transformation ratio that provides a slight increase in the transformable voltage. Moreover, the device provides a sufficiently large suppression of those interference, the frequency of which is higher than 5 Hz, especially since these interference in themselves have a lower level.

 The voltages of the useful signals having frequencies above 0.4 kHz and falling into the delay band of the half-link of the low-pass filter 2 pass through the filter to the direct input of the op-amp 1 with significantly greater attenuation than through the other circuit to the inverse input. When the difference ratio of the voltages supplied to both inputs OK 1, these voltages are not suppressed, but amplified. Thus, the interference suppression device simultaneously functions as a linear amplifier of the receiving path of communication equipment with adjustable gain of useful signals by changing the resistance of the variable resistor 8 in the negative feedback circuit of the OS 1.

 An increase in the signal-to-noise ratio in the considered device is achieved not only due to the property of the op-amp significantly suppress common-mode voltages. Whereas in a conventional linear amplifier of communication equipment, not only useful signals are undesirably amplified, but also interference, in a linear amplifier in the form of the device in question, the compensated reduced noise level does not increase, only useful signals are amplified, and an additional increase in the signal-to-noise ratio at the output of communication equipment is provided by increasing only the numerator of the ratio in the absence of an increase in the denominator.

 (56) Mikhailov M.I. and Razumov L.D. Protection of cable communication lines from the influence of external electromagnetic interference. M.: Communication, 1967, p. 319 and 320, p. 10.58.

Claims (1)

 DEVICE REDUCTION DEVICE IN COMMUNICATION EQUIPMENT, comprising an amplifier and a phase shifter, characterized in that, in order to increase the signal / noise ratio at the output of the device, a low-pass filter (LPF) half-link with a passband of 0 - 0.4 kHz and a voltage resistor divider are introduced wherein the amplifier is made in the form of an operational amplifier, the direct input of which is connected to the output of the resistor voltage divider, the inverse input of the operational amplifier is connected to the input of the low-pass filter of the low-pass filter and is the input of the device, the output of the half-link The low-pass filter is connected through the phase shifter to the input of the voltage divider, while the phase shifter is designed as a small-sized transformer, and the entire device is included in the communication equipment instead of a linear amplifier of the receiving path.