RU2402874C2 - Amplitude telegraphy signal incoherent reception device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: device for incoherent reception of amplitude telegraphy (AT) signals has cascade-connected band-pass filter, intermediate frequency amplifier connected in an automatic gain control circuit, amplitude detector, low-pass filter and threshold element. The automatic gain control circuit comprises cascade-connected count pulse generator with fixed threshold, pulse counter, adder, register and digital-to-analogue converter, as well as a logic OR element and an XOR element, wherein the initial state of the pulse counter is characterised by a number M=f₀ T_s, where f₀ is the AT signal-carrier frequency, T_s is duration of the element of the AT signal. Use of discrete elements in the automatic gain control circuit enables to keep parameters of the receiver constant on the interval of each elementary transmission of the AT signal and their measurement at the boundary between transmissions in accordance with results for continuous analysis of the ratio of the signal level and interference at the output of the intermediate frequency amplifier.

EFFECT: higher noise immunity of receiving amplitude telegraphy signals.

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Description

The invention relates to communication technology and can be used for recording reception of amplitude telegraphy signals.

A device is known for receiving amplitude telegraphy signals, comprising a cascade-connected bandpass filter, an amplifier, an amplitude detector, a low-pass filter, a balancing stage and a threshold element, the output of which through the pause protection node is connected to the control input of the balancing stage, and the output of the amplifier is also connected to the detector automatic gain control system, the output of which through the integrating element is connected to the control input of the amplifier [1].

The disadvantage of the device, as noted in [1], is the relatively low noise immunity of the reception. This is due to the fact that when receiving the amplitude telegraphy (AT) signal, the threshold principle of reproducing transmitted signals is used. Moreover, the value of the optimal response threshold depends both on the amplitude of the signal at the output of the intermediate frequency amplifier (IFA), and on the rms value of the noise in the communication channel. In the aforementioned device, the balancing cascade, together with the IF, covered by the automatic gain control (AGC) circuit, provides insufficiently accurate “tracking” of the optimal registration threshold when the interference situation in the communication channel changes.

The closest in technical essence to the claimed is a device for receiving AT signals, containing a cascade-connected bandpass filter, amplifier, amplitude detector, low-pass filter and threshold element, as well as a quadratic detector, the input of which is connected to the output of the amplifier, and the output through an integrating element connected to the control input of the amplifier, in addition, between the output of the quadratic detector and the control input of the threshold element included cascade-connected cubic cascade, integrator and Tel threshold [2].

The disadvantages of this device, selected as a prototype, are [3]:

- there is a change in the voltage level at the outputs of the integrators and, accordingly, the threshold shaper on the interval of the duration of the signal element, due to the fact that the AT signal in total with interference belongs to the class of non-stationary random processes;

- the difficulty of the technical implementation of the threshold shaper, the amplitude characteristic of which is described by a rather complex mathematical expression.

The noted disadvantages lead to an error in measuring the ratio of the signal level to the noise level at the output of the amplifier and impair the noise immunity of receiving AT signals.

The aim of the claimed device is to increase the noise immunity of receiving AT signals while simplifying the receiving device.

This goal is achieved by the fact that in a device containing a cascade-connected bandpass filter, an amplifier with a controlled gain, an amplitude detector, a low-pass filter and a threshold element, cascade-connected counting pulse shaper, pulse counter, adder are included between the output of the IF and its control input , a register and a digital-to-analog converter, where the adder inputs are connected on one side to the meter outputs and, on the other hand, to the register outputs, the register control input is connected with the output of a two-input OR logic element, one of the inputs of which is connected to the output of the write pulse shaper, and the second input is connected to the exclusive OR output of the logic element, whose inputs are connected to the two upper bits of the pulse counter, the control input of the latter through the write pulse shaper is connected to the threshold output item.

A comparative analysis of the claimed device and its prototype showed that the controllable pulse counter, adder and register with a digital-to-analog converter are not used in the prototype, and the claimed device meets the criteria of “novelty” and “significant” differences.

The use of a register with a digital-to-analog converter in the claimed device leads to a positive effect, which consists in ensuring a constant voltage at the control input of the frequency converter over the interval of the duration of the information packet, and a pulse counter with an adder provide more accurate "tracking" of the optimal registration threshold than in known devices.

The newly introduced features make it possible to increase the noise immunity of receiving signals of amplitude telegraphy, bringing it closer to optimal.

The invention is illustrated by drawings, where figure 1 shows a functional diagram of a device for incoherent reception of a signal of amplitude telegraphy, figure 2 is a timing diagram of a signal X (t) at the output of an intermediate frequency amplifier.

The device comprises a cascade-coupled band-pass filter 1, an intermediate-frequency amplifier with a controlled gain (UHF) 2, an amplitude detector 3, a low-pass filter (LPF) 4, a threshold element 5. The UHF 2 is covered by a cascade-connected automatic gain control circuit pulse counting generator (FSI) 6, pulse counter 9, adder 13, register 14, digital-to-analog converter (DAC) 8. The output of the FSI 6 is connected to the input of the counting counter 9. The inputs of the adder 13 are connected to the outputs on one side the counter 9, and on the other hand with the outputs of the register 14. The control input of the register is connected to the output of the logical element OR 11, one of the inputs of which is connected to the output of the pulse shaper write (PP) 7. The second input of the element OR 11 is connected to the output of the logical element exclusive OR 10. The inputs of element 10 are connected to the two high-order bits of the counter 9. The input of the preliminary recording of the counter 9 through the pulse shaper of record 7 is connected to the output of the threshold element 5. The inputs of the parallel recording of the counter are connected to the unit for starting flax state (ONS) 12.

The device operates as follows. The input signal, which is the sum of the amplitude-manipulated harmonic oscillation and additive interference, is fed through a band-pass filter 1 and the IF 2 to the input of the amplitude detector 3. The amplitude detector 3 together with the low-pass filter 4 converts the amplitude-modulated oscillation into a video signal that is fed to the input of the threshold element 5 with a fixed threshold. The threshold element 5 converts the distorted video signal into rectangular pulses with a standard amplitude.

The signal X (t) from the output of the amplifier 2 is also fed to the input of the counter pulse shaper 6 with a fixed threshold. In figure 2, the signal X (t) is shown in the form of a time diagram. An analysis of the situation shown in Fig. 2 leads to the conclusion that, with an optimal response threshold U _{n, the} number of pulses at the output of the FSI 6 at a time interval of 2T is f ₀ · T _s , where f ₀ is the carrier frequency of the signal, T _s is signal element duration. If the number of pulses N at the output of the FSI 6 is less than f ₀ · T _s , it is necessary either to decrease the value of U _n or to increase the gain of the IF amplifier 2. Since the second option does not require additional complication of the device as a whole (the implementation of the FSI with a fixed threshold is simpler than with changing) it is taken as the basis for the construction of the inventive device. It should be noted that the degree of necessary change in the gain of the IF 2 is unambiguously related to the difference f ₀ · T _s −N. This difference is determined using a pulse counter 9. This occurs as follows. At time t = 0, there is a positive voltage drop at the output, which is fed to the input of the recording pulse shaper 7. The resulting pulse from the output of the PHI 7 goes to the control input of counter 9. Due to this, the number M takes place in the counter the output of ONS 12. The value of the number M must satisfy the condition M = f ₀ · T _s (the required number M is set in ONS 12 using a set of jumpers). After that, with the arrival of each pulse from FSI 6, the number recorded in counter 9 decreases by one. By the time t = 2 T, at the output of the counter, there is a number f ₀ · T _s -N, represented in binary code, which is input to the adder 13. The second input of adder 13 receives the number R from the output of register 14. With the appearance of the following positive the difference at the output at time t = 2T by the signal from the output of the OR element 11, the updated number R is recorded in register 14. Using the DAC 8, this number is converted to an analog value, which in the form of the AGC voltage is supplied to the control input of the amplifier 2, due to which increases the gain Y B, approaching the optimum. For N> f ₀ · T _{s, the} number R recorded in register 14 will decrease, which will lead to a decrease in the gain of the gain. At N = f ₀ · T _{s, the} number R, and, accordingly, the gain of the IF amplifier, remains unchanged.

It should be noted that a situation is possible when, at the time of the next positive voltage drop at the output, there was not an alternation of packages and pauses, but a long pause. In this case, at the optimal gain, the number M recorded in the counter 9 to the arrival of the positive edge will change slightly. If no measures were taken, this would lead to a significant change in the number R in the register 14, and, accordingly, to a change in the gain of the amplifier. To prevent this possibility, an exclusive OR 10 logic element was introduced. The fact is that with a slight change in the number M, the voltage levels at the upper bits 7, 8 of the counter correspond to the potentials of a logical unit and a logical zero. Therefore, at the output of element 10 (at the input of element 11), the potential of a logical unit takes place. This "prohibits" the passage of the pulse from the output of the physical protection element 7 to the control input of the register 14. Thus, the element 10 together with the element 11 prevents false operation, which could lead to the "departure" of the gain of the IF amplifier from the optimal one. A similar function is performed by the pause protection circuit in the device described in [1].

Another situation is possible. For simplicity, consider a specific example. Let the following combination of parcels and pauses take place on some part of the time axis: “0”, “1”, “1”, “0”, “1” (“0” corresponds to a pause, “1” to a parcel), and f ₀ · T _s = 100 (i.e., 100 periods of the carrier oscillation fit in the interval Ts). In this case, the counter 9 at the time of the first transition from "0" to "1" is written the number M = f ₀ · T _s = 100. With the optimal gain in the time interval T _s , on which the first parcel takes place, the number recorded in the counter will decrease by approximately f ₀ · T _s = 100. Over the next period of time of 2T _s , on which there is an alternation of "1" and "0", this number will decrease by another f ₀ · T _s = 100. Thus, by the time of the next positive difference, the contents of the counter are Мс = М-2 f ₀ · T _s = 100-200 = -100. In this case, the potentials on the digits 7, 8 of the counter correspond to the levels of logical zero and logical units. Therefore, at the output of element 10, and, accordingly, at the input of element OR 11, the potential of a logical unit takes place. This prevents the passage of the pulse from the output of the physical protection element 7 to the control input of the register 14. Therefore, the gain of the IF amplifier in this case also remains unchanged.

From the above description it follows that the claimed device does not contain previously unknown blocks and elements. The inventive device allows adaptation to a changing interference situation in the communication channel for a time interval equal to twice the duration of the elementary package. This ensures that the gain of the amplifier remains constant over the interval of the duration of the package, thereby achieving greater accuracy in setting the optimal gain of the amplifier. This, in turn, helps to ensure reception noise immunity close to noise immunity of optimal incoherent reception of AT signals.

Information sources

1. N. A. Sartasov and others. Short-wave trunk radio receivers. M .: "Communication", 1971, p.142-146, Fig.4.3.

2. Copyright certificate of the USSR No. 665405, cl. HB04 1/10, 1979.

3. Smirnov A.V., Prozorovsky E.E., Bulakh N.N. Incoherent reception of amplitude telegraphy signals with a tracking threshold. - On Sat "Issues of the formation and processing of signals in radio systems." Issue 1. Taganrog, 1976, p. 58-63.

Claims (1)

A device for incoherent reception of amplitude telegraphy (AT) signals, comprising a cascade-connected bandpass filter, an intermediate-frequency amplifier covered by an automatic gain control circuit, an amplitude detector, a low-pass filter and a threshold element, characterized in that the automatic gain control circuit is implemented in cascade -connected shaper of counting pulses with a fixed threshold, pulse counter, adder, register and digital-to-analog converter, the output of The counter pulse generator is connected to the counter countdown input, the second adder input is connected to the register output, the register control input is connected to the output of the OR logic element, one of the inputs of which is connected to the output of the recording pulse generator, and the second input is connected to the output of the exclusive OR logic element, the inputs of which are connected to the two high-order bits of the pulse counter, the output of the threshold element is connected to the input of the recording pulse shaper, the output of the recording pulse shaper is connected to the control yuschemu input pulse counter, the initial state is characterized by the number M = f ₀ T _s, where f ₀ - AT carrier frequency signal, T _s - signal element duration AT.

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