RU1774515C - Demodulator of frequency-modulated signals - Google Patents

Abstract

The demodulator contains an amplifier-limiter 1, a single-shot 2, two And 3,4 elements, a trigger 5, two inverters 6,7, a frequency detector 8, a delay unit 12, a balanced mixer 13, a band-pass filter 14, a detector 15, a threshold block 16, electronic key 17. 1-3-5, 1-8-2-6-3, 1-2-6, 2-4-5, 1-7-4, 17-12-13, 1-13-14- 15-16-17-4, 17-3. Zil.

Description

The invention relates to radio engineering and can be used in radio receivers.

As a prototype, a demodulator of frequency-manipulated signals according to ed. No. 1145488, comprising an amplifier-limiter, a one-shot, two And elements, a frequency discriminator, a low-pass filter, an amplifier, a trigger, the inputs of which are connected to the outputs of the And elements, an inverter connected between the outputs of the one-shot and the first input of the first And element, while the second input the first element And is connected to the output of the amplifier-limiter, and the first input of the second element And is connected to the output of the single-vibrator, the input of the single-vibrator is connected to the output of the amplifier-limiter, between the output of the amplifier-limiter and the second input torogo element and included an additional inverter and series-connected frequency discriminator, the low-pass filter and amplifier

DC, and the input of the frequency discriminator is connected to the output of the amplifier-limiter, the output of the DC amplifier is connected to another input of the one-shot.

The disadvantages of this prototype device include low noise immunity when exposed to selective and pulsed interference.

The purpose of the invention is to increase noise immunity when exposed to selective and pulsed interference.

This goal is achieved due to the fact that in the demodulator of frequency-manipulated signals containing a limiter amplifier, a single-shot, two And elements, a trigger, the inputs of which are connected to the outputs of the And elements, an inverter connected between the output of the one-shot and the first input of the first And element, this second input of the first element And is connected to the output of the amplifier-limiter, and the first input of the second element And is connected

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with the output of a single-shot, the input of a single-shot is connected to the output of the amplifier-limiter, between the output of the amplifier-limiter and the second input of the second element And an additional inverter is included, as well as a series-connected frequency discriminator, a low-pass filter and a DC amplifier, the input of the frequency discriminator connected to the output of the amplifier-limiter, the output of the DC amplifier connected to the other input of the single-shot, introduced in series connected delay unit, balanced mixer, p losovoy filter, a detector, a threshold unit, and an electronic key, wherein the delay unit input and a second input of the balanced mixer are input demodulator keyer output being coupled to the third inputs of AND gates,

FIG. 1 is a structural diagram of a demodulator of frequency-manipulated signals.

The demodulator contains an amplifier-limiter 1, a single-vibrator 2, elements And 3, 4, a trigger 5, inverters 6, 7, a frequency detector 8, consisting of a frequency discriminator 9, a low-pass filter 10, a constant current amplifier 11, a delay unit 12 , balanced mixer 13, band-pass filter 14, detector 15, threshold block 16, electronic key 17.

Figure 2 shows timing diagrams of signals illustrating the operation of a demodulator of frequency-manipulated signals.

Ui is the signal at the input of amplifier-limiter 1, at time t 0 there is a transition from frequency B corresponding to package O to frequency fA corresponding to package 1, and at time t ti there is a transition from f d to TB, which corresponds to transmission the parcels

Ua, Uz - signals at the output of the amplifier - limiter 1 and inverter 7, respectively:

1) 4, Us signals at the output of one-shot 2 and inverter 6, respectively;

Ue, U, Us - signals at the output of circuits And 3, 4 and trigger 5, respectively, provided that the output of the electronic key 17 is not connected to the inputs of circuits And, t, e. in this way, the demodulator works without introducing a delay unit, mixer, bandpass filter, detector, threshold unit and electronic key.

The plots fi and fa show the change in the frequency at the inputs of the balanced mixer 13. During the time rf determined by the delay unit 12, a signal with a frequency Af is present at the output of the bandpass filter tuned to the difference frequency Л f fA - fs, which is detected and supplied to the threshold block.

Ug is the signal at the output of the electronic key 17. (

Ue, U, Us - signals at the outputs of circuits AND 3, 4 and trigger 5, respectively, at

0 provided that the output of the electronic key 17 is connected to the inputs of circuits I.

Fig. 3 shows timing diagrams of signals for a demodulator operating in the presence of interference.

5 At time t2 during transmission 1 under the influence of interference, the frequency briefly changes in the direction of decrease, and at time tz during transmission of O, in the direction of increase. If the output of the electronic key 17 is not connected to the inputs of the circuits AND 3, 4, the output signal Ua of the trigger 5 contains errors. When connecting the blocks entered into the device, these errors are eliminated, as shown in the diagram Us.

5 The invention is illustrated by the following operation description example.

The output frequency-shift signal with the help of amplifier-limiter 1 is converted into rectangular pulses. Each pulse of the obtained sequence with its leading edge is triggered by a single vibrator 2. The pulse duration of a single vibrator 2 is equal to the half-cycle of the center frequency. The pulses of one vibrator 2 and an amplifier-limiter 1 of variable duration are separated by an And 3 element with an inverter 6 on the one hand and an And 4 element with an inverter 7 on the other side according to the sign of the difference in duration and are converted into pulses with a duration depending on the frequency and lasting during the modulation period. Separated pulses are fed to the inputs of trigger 5 and control its operation,

5 Permission for the passage of separated pulses through the elements And 3, 4 is carried out by a logical unit from the output of the electronic key 17, which is formed only when the sign of the manipulations changes for a period of 2-3 periods of frequency shift.

To generate a signal that controls the operation of the electronic key 17, connected to the input of the demodulator

5, one of the inputs of the balanced mixer 13. The second signal of the balanced mixer 13 is supplied with the same signal as the first, but with a delay determined by the time delay unit 12 During the time gs, which is chosen equal to 2-3 periods of the frequency shift, at the output a bandpass filter 14 with a tuning frequency equal to the frequency of the frequency shift, a signal appears through the detector 15 and the threshold block 16 to the input of the electronic key 17. The role of the threshold block 16 can play, for example, a tunnel diode, which in the absence of a signal at the output detects The vector 15 is in the low-voltage state, and if there is a signal at the output of the detector, it goes into the high-voltage state. The electronic key is a transistor to the base of which a tunneling diode is connected. The operating point of the transistor is selected so that it is open when the tunnel diode is in a low voltage state. The collector of the transistor is connected to the inputs of circuits And 3 and 4, and at these inputs there is a logical 1 only when the transistor-electronic key 17 is closed, and only then trigger 5 changes its state.

When the center frequency drifts due to the instability of the radio line, the frequency detector 8 emits a voltage proportional to the center frequency drift, the pulse width of one-shot 2 tracks half the period

center frequency. When the frequency of the input signal changes due to pulsed and selective interference, the voltage at the output of the filter 14 is not enough to trigger the threshold device 16, the key 17 outputs a logic zero, and trigger 5 retains its previous state.

Thus, a change in the state of the output trigger 5 occurs when the frequency of the input signal changes only by an amount equal to the frequency of the frequency shift, i.e. The frequency of change in the state of the trigger corresponds to the period of manipulation and does not depend on the presence of interference.

Claims (1)

SUMMARY OF THE INVENTION Demodulator of frequency-manipulated signals by autosw. N ° 1145488. characterized in that, in order to increase the noise immunity under the influence of selective and pulsed interference, a delayed block, a balanced mixer, a bandpass filter, a detector, a threshold block and an electronic key are introduced in series, the input of the delay block and the second input of the balanced mixer are the input of the demodulator, the output of the electronic key is connected to the third inputs of elements I. Fig / Fhg. 2 Fie.