SU734884A1 - Noise suppressor - Google Patents

Description

(54) DINING SUPPLIER

The invention relates to radio engineering and can be used in communication devices to automatically turn on or turn off terminal devices depending on the quality of the input signal, usually estimated by the signal-to-noise ratio. In particular, the proposed noise suppressor can be used in radio receivers to eliminate the tedious effect of noise on the operator. A squelch is known, including a high-pass filter, an amplifier and a noise detector, a device, calculating our ratio of signal voltage to noise voltage, and an analog switch. In this device, the noise voltage is allocated by a high-pass filter, the bandwidth of which does not include the composition of the transmitted signal. This noise voltage is amplified, rectified, and fed to a device that calculates the ratio of the signal voltage to the noise voltage, the signal from which controls the operation of the analog switch 1. The disadvantage of this device is the need for a wider bandwidth prior to that compared to the width of the spectrum of the transmitted message, the low and unstable sensitivity of the detection of the information signal against the background noise and low speed associated with the need to straighten and fil tration analyzed signals. The latter can lead to distortions of the transmitted message. The closest in technical essence is a device containing a driver that converts an analog input signal into a digital one, the counter of periods of the input signal over a time determined by a clocking circuit operated by a master oscillator. The circuit also contains a prohibition element and a turn-off delay counter that controls the analog key 2. A drawback of the device is a narrow control range of the threshold signal-to-noise ratio, which for this device is approximately equal to 1. The control of the threshold signal-to-noise ratio of this device can be done by measuring - not counting the volume of the counter of the number of periods of the input signal or by changing the frequency of the master oscillator. However, if the number of periods increases by more than 10%, the circuit will perceive the noise signal as informational. When reducing the number of periods in the counter, part of the working signal spectrum will be perceived by the circuit as a noise signal, which will lead to partial loss of information. If the input signal is a fixed frequency, for example, when receiving a telegraph signal tinted by the frequency direction, then if the volume of the number of periods counter decreases, there may be a complete loss of information. A change in the frequency of the master oscillator leads to the same results, and the switch-off delay time changes. The purpose of the invention is to expand the control range of the threshold signal-to-noise ratio. To do this, the noise suppressor contains an input signal period counter, the counting input of which is connected to the output of the driver, the zeroing input to the first output of the clocking circuit, and the output to the first input of the inhibit element the second input of which is connected to the first output of the clocking circuit, the third input to the output of the delay counter, the first you .had to the control input of the analog switch, and the second output to the zero input of the delay counter, counting The input of which is connected via the clocking circuit to the output of the master oscillator, a low-frequency noise generator and an analog adder are entered, the first input of which is connected to the output of the low-frequency noise generator, the second input is combined with the signal input of the analog key and is the device input, and the output is connected with shaper inlet. The drawing shows a structural electrical circuit, noise suppressor. The device contains a driver 1, converts an analog signal into a digital signal, the output of which is connected to the counting input of the counter 2 periods of the input signal. The zeroing input of the counter 2 is connected to the first output of the clocking circuit 3, which operates from the master oscillator 4. The output of the counter 2 is connected to the first input of the prohibition element 5, the second input of which is connected to the first high circuit of the clocking circuit 3, and the third input to the output of the counter 6 shutdown delays. The counting input of the counter b is connected to the second output of the clocking circuit 3, and the zeroing input of the counter b is connected to the first output of the prohibition element 5, the second output of which is connected. It is not connected with the control input of the analog switch 7. The signal input of the analog switch 7 is connected to one. from the inputs of the analog sum 8), another input of the adder 8 is connected to the noise of the generator 9 low frequency 734884 noise with an adjustable output voltage level, and the output of the summer 8 to the input of the driver 1. The noise suppressor input is the connection point of the signal input of the analog switch 7 and one of the inputs of the analog adder 8. The output of the noise canceller is the output of the analog switch 7. The noise canceller operates as follows. . The mixture of signal and noise enters the input of the noise canceller and simultaneously arrives at the signal input of the key 7 and one of the inputs of the adder 8, to the other input of which the adjustable noise voltage from the noise generator 9 arrives. . . The resulting mixture from the output of the adder 8 is fed to the input of the former 1, which produces pulses for each positive crossing of the zero line by applying the voltage of the mixture. The pulses from the output of the imaging unit 1 are fed to the counting input of counter 2, which accumulates them for a period of time determined by the follow-up period of the discharge pulses fed to the obnuyushchy input of the counter 2 from the first output of the clocking circuit 3, to the input of which 4. The pulse repetition period TO is about tens of milliseconds and determines the speed of the noise suppressor, and the volume of the counter 2 is chosen from the condition Nc4.2.0,9 Fu.cp.-To, where РШ.СЬ, is the average noise frequency noise input Ate, NcM.a is the volume of counter 2. In the case of counter 2 overflowing, pulses from its output go to the first input of prohibition element 5, which at the same time prohibits the passage of reset pulses from the first output of the clocking circuit 3 to the zeroing input of counter 6, which accumulates pulses received at its counting input from the second output of the clocking scheme 3 and the corresponding zero-out cycles of the counter 2. The volume of the counter b was chosen from the condition. .NC4.6 T „/ Where Nc4.6 is the volume of the counter 6, TH is the average duration of the pause-speech signal. If counter 2 overflows with the cycle for the number of cycles greater than Ncn.e, then the described mechanism of operation of prohibition element 5 and counter 6 causes the latter to overflow. The impulse from its output changes the state of the prohibition element 5, which switches the key 7 to the “off” state. the signal from the input of the noise suppressor does not pass to its output. This happens if the resultant mixture consisting only of noise or a signal-to-noise ratio less than unity enters from the output of adder 8 to the input of shaper I for a time greater than Tn, which indicates that at the input of the noise suppressor signal-to-noise ratio less than the specified threshold value defined by the expression

 Vl + (ishg / ish.bh)

(U (j / Uiji) BX.HO | J.

i where and shg

- noise voltage of the noise generator;

UUI.BX is the noise voltage at the input of the noise suppressor.

In this case, the pulse frequency from the generator 1 output is such that the counter 2 overflows during the time between two zeroing pulses.

When the signal-to-noise ratio at the input of the squelch is greater than the specified threshold value, and accordingly the signal-to-noise ratio of the resulting mixture at the input of imaging unit 1 is greater than one, the pulse frequency from its output is such that counter 2 does not overflow during the time between two zeroing pulses. In this case, the prohibition element 5 permits the passage of reset pulses from the first output of the clocking circuit 3 to the zero reset input 6 and changes its state to the opposite, transferring the key 7 to the "switched on." Signal from the input of the noise canceller passes to its output. During the natural pauses of a speech signal with a duration of not more than Tn, prohibition element 5 does not have time to change its state and maintains key 7 in the "on" state. This is because during this time

The counting input of counter 6 from the second output of the clocking circuit 3 will receive a number of pulses less than Msb. The counter b will not overflow and after the end of the pause, it will pulse out from the first output of the clocking circuit 3.

Claims (2)

1.Shvartsman A. R. On some schemes of noise suppressors. “Questions of radio electronics, series TRS, 1974, no. 1, s. 170-174. 2. US patent number 3902123, cl. 325-478, 1975 (prototype).