RU1840892C - Frequency-modulated signal transmitter - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: transmitter comprises series-connected integrator, phase modulator, frequency multiplier, power amplifier and antenna, as well as series-connected synchroniser and modulator, the output of which is connected to the other input of the power amplifier, and the output of the synchroniser is connected to the input of a modulating signal source, wherein the other input of the phase modulator is connected to the output of a crystal oscillator, and the output of the integrator is connected to the input of a discharge device, wherein a pulse envelope selecting device and a switch are connected in series between the output of the modulating signal source and the input of the integrator, wherein a delay device is connected between the output of the modulating signal source and the input of the integrator, and the other input of the switch is connected to the output of the discharge device.

EFFECT: reduced distortion of information during transmission and more reliable reception of said information.

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Description

The proposed transmitter of frequency-modulated signals relates to the field of radio engineering and radar and is intended for use in radio communication systems, mutual exchange of information and mutual orientation, as well as in active radar.

A known transmitter with an indirect method of obtaining frequency modulation (see Vereshchagin EM, Nikitenko Yu.G., Frequency and phase modulation in communication technology. M .: "Communication", 1974, p. 20). The transmitter contains a source of modulating signals, an integrator, a phase modulator, a crystal oscillator, a frequency multiplier, a power amplifier and is designed to transmit broadband signals, for example, discrete signals, consisting of a series of rectangular pulses of various durations.

The specified device, in which frequency modulation (FM) is obtained by conversion from phase modulation (FM), has a drawback, namely, a parasitic shift in the average frequency of the FM transmitter is observed for any modulating signal containing a constant component, as a result, the stability of the average frequency of the FM the transmitter.

This phenomenon is explained by the accumulation of charge on the capacitor of the integrator and, accordingly, a decrease in the rate of rise of voltage on this capacitor. The law of variation of the average frequency at the output of the transmitter

. $$\Delta f_{\mathrm{from}m}(t)=\frac{\Delta f_d}{q}(\mathrm{one}-e^{-\frac{t}{T}})$$

.

So, for example, with a modulating signal with a duty cycle

q = 2 Δf _cm = 0.5Δf _d .

Figure 3 presents the timing diagrams of the transmitter, where:

a) - modulating pulses;

b) - voltage at the output of the integrator;

c) - frequency change at the output of the FM transmitter;

Δf _d - useful frequency deviation;

- установившееся смещение частоты; $$\frac{\Delta f_d}{q}$$

- steady-state frequency offset;

T is the integrator time constant.

The value of the useful frequency deviation at the output of the transmitter does not change, however, the average frequency shifts relative to the carrier frequency of the crystal oscillator in the opposite direction relative to the useful frequency deviation.

The FM transmitter of the VZOI-VZOR system has significant disadvantages.

1. When modulated by pulsed rectangular signals, the parameters of the integrator and phase modulator significantly affect the distortion of the shape of the transmitted signal. At the transmitter output, there is a deviation (throws) of the frequency of the opposite sign with respect to the useful frequency deviation after the end of the modulating pulse, several times higher than the useful deviation. This is due to the fast discharge of the capacitance of the integrator through an open diode, which is connected in parallel to the resistor of the integrating target with reverse polarity for the modulating unipolar pulse signal. The diode is turned on to improve the stability of the average frequency of the FM transmitter during the transmission of pulsed signals containing a constant component.

Information distortions appearing after the integrator and phase modulator are further increased in the subsequent multiplier-amplification path, which is associated with its limited broadband. At the same time, it is practically impossible to restore the original form of transmitted impulse information when it is received.

In FIG. 4 shows the timing diagrams of the operation of the VZOI - VZOR transmitter, where:

a) - modulating pulses;

b) - voltage at the output of the integrator;

c) - frequency change at the output of the FM transmitter.

2. Deviation (throws) of the frequency of the opposite sign with respect to the useful deviation significantly complicates the work of the FM receiver and can lead to a partial or even complete loss of transmitted information. It is necessary to install diode limiters at the output of the receiver discriminator, as well as fulfill special requirements for the construction of an intermediate frequency amplifier (IF) and a video amplifier, which complicates the construction of the receiver.

3. Significantly increased the radiation spectrum of the transmitter, which negatively affects the fulfillment of the compatibility conditions of radio systems installed at the facility, as well as the noise immunity of these systems.

The aim of the present invention is to reduce the distortion of information during transmission and increase the likelihood of its reliable reception while maintaining high stability of the average frequency of the frequency-modulated signals by eliminating the deviation of the frequency of the opposite sign with respect to the useful deviation.

This goal is achieved by the fact that in the transmitter containing the power amplifier connected to the antenna, a synchronizer, one output of which is connected to the source of modulating signals, and the other through a modulator with the first input of the power amplifier, a phase modulator, the first input of which is connected to the output of the integrator and the discharge target input, the second input with a crystal oscillator, and the output through the frequency multiplier connected to the second input of the power amplifier, a pulse envelope extraction device, a key circuit and a back line are introduced rzhki, wherein the two inputs of gating circuit connected respectively to the output of the pulse envelope detection apparatus and the outlet of the discharge target, and an output connected to the input of the integrator and the output of the delay line, the source baseband output coupled to the input of the delay line and the input of the pulse envelope detection apparatus.

Introduction to the transmitter of frequency-modulated signals of the pulse envelope extraction device, the key circuit and the delay line reduces information distortion during transmission and increases the probability of its reliable reception while maintaining high stability of the average frequency of the frequency-modulated signals by eliminating the deviation of the frequency of the opposite sign with respect to useful deviation , which became possible due to the introduction of a key device into the known device, which interferes with the operation of the discharge target of the integrator during transmission pulse discharge information and provides an integrator signal at the end of transmission of the pulse envelope detection apparatus, as well as delay line pulse information to the response time of the gating circuit and pulse envelope detection apparatus.

The invention is illustrated by drawings, which represent:

in FIG. 1 is a block diagram of a proposed transmitter of frequency-modulated signals;

in FIG. 2 - time diagrams of the operation of the transmitter of frequency-modulated signals;

in FIG. 3 - time diagrams of the operation of the transmitter (analogue);

in FIG. 4 - timing diagrams of the transmitter VZOI - VZOR (prototype).

The frequency-modulated signal transmitter (Fig. 1) contains a modulating signal source 1, a delay line 2, an integrator 3, a phase modulator 4, a crystal oscillator 5, a frequency multiplier 6, a power amplifier 7, a modulator 8, a pulse envelope extraction device 9, a key circuit 10, a discharge circuit 11, a synchronizer 12, and an antenna.

The power amplifier 7 is connected to the antenna. One output of the synchronizer 12 is connected to the source of modulating signals 1, and the other through a modulator 8 is connected to the first input of the power amplifier 7. The first input of the phase modulator 4 is connected to the output of the integrator 3 and the input of the discharge circuit 11, the second input is connected to the crystal oscillator 5, and output - through a frequency multiplier 6 is connected to the second input of the power amplifier 7. Two inputs of the key circuit 10 are connected respectively to the output of the pulse envelope extraction device 9 and the output of the discharge circuit 11, and the output is connected to the input of the integrator 3 and 2 delay line progress. The output of the source of modulating signals 1 is connected to the input of the delay line 2 and the input of the pulse envelope extraction device 9.

The specific implementation and operation of the frequency multiplier, power amplifier, modulator, synchronizer and delay line are described in the scientific and technical literature. In the book Vereshchagin E.M., Nikitenko Yu.G. “Frequency and phase modulation in communication technology”, M .: “Communication”, 1974, a phase modulator, a crystal oscillator and an integrator are described in sufficient detail. The source of modulating signals is based on elements of discrete technology and, depending on the type of transmitted message, produces various code pulse sequences. The device for extracting the envelope of pulses is also made on elements of discrete technology and is triggered by impulses of the beginning and end of the transmitted message according to their distinguishing features from the rest of the message pulses. The key circuit is made on an integrated circuit, and the discharge circuit is on resistors and semiconductor diodes.

The transmitter frequency-modulated signals operates as follows. When it is turned on, at both outputs of the synchronizer 12 signals appear corresponding to the operation of the transmitter in the mode of transmitting code, pulse information. The signal from the first output of the synchronizer 12 is fed to the input of the source of modulating signals 1. At the same time, the pulse code information intended for transmission to another moving object appears at the output of the source of modulating signals 1, enters the device for selecting the envelope of pulses 9 and the input of the delay line 2. At the time from the beginning of the first pulse of code information to the end of the last pulse of code information at the output of the device for extracting the envelope of pulses 9, a pulse arrives at the first input of the key circuit 10. The action of this pulse is such that the key circuit 10 disconnects the output of the discharge circuit 11 from the input of the integrator 3, i.e. carries out a closed circuit "integrator - discharge circuit - key circuit".

To convert FM to FM between the input of the modulating signal and the phase modulator 4, an integrator 3 is included.

The time constant of the charge of the integrator 3 is selected 8 ÷ 10 times greater than the maximum transmission time of the code information. The fulfillment of this condition provides a constant rate of voltage change at the integrator 3 upon receipt of each subsequent pulse of information. In order to prevent information pulses from entering the integrator 3 input before the integrator-discharge-circuit-key circuit circuit is broken, an information pulse delay line 2 is activated between the modulating signal source 1 and integrator 3 for the duration of the operation of the pulse envelope extraction device 9 and key scheme 10.

An indirect FM method is used in the transmitter, so the integrated pulses of code information are fed to the first input of the phase modulator 4. To obtain a stable carrier frequency, a crystal oscillator 5 is connected to the second input of the phase modulator 4. The frequency-modulated signal from the output of the phase modulator 4 is fed to the multiplier frequency 6 to obtain the nominal output frequency of the transmitter and the heterodyne signal of the receiver.

The signal from the second output of the synchronizer 12, equal in duration to the transmission time of the pulse code information, is fed to the input of the modulator 8, which provides at this time the rated mode of operation of the power amplifier 7.

An amplified frequency-modulated signal enters the antenna and is emitted into free space. At the moment of the end of the last pulse of the transmitted code information, the pulse disappears at the output of the pulse envelope separation device 9, the action of which on the key circuit 10 was closing and the circuit "integrator - discharge circuit - key circuit" closes.

After the transfer of information, the transmitter signals of the synchronizer 12 is transferred to the mode of receiving information of another moving object. In this case, according to the signal from the first output of the synchronizer 12, the source of modulating signals 1 is disconnected from the delay line 2 and the device for selecting the envelope of pulses 9. The signal from the second output of the synchronizer 12, equal in duration to the time of receiving information, is fed to the input of the modulator 8, which at that time is already does not provide the nominal mode of operation of the power amplifier 7 (for example, the first voltage anode of the traveling wave lamp of the power amplifier 7 does not receive the rated supply voltage and 100% gating of the output power of the transmitter occurs Single information on the reception by the receiver). During the transient processes occurring in the modulator 8 and the power amplifier 7 when the FM transmitter passes from the information transfer mode to the receive mode, the integrator is discharged and its transition to its initial state.

The rate of change (decrease) in the voltage at the integrator is such that it does not cause a carrier frequency shift at the output of the transmitter after the end of the last pulse of the transmitted code information. In FIG. 2 shows the timing diagrams of the operation of the transmitter of frequency-modulated signals where:

a) modulating pulses;

b) the voltage at the output of the integrator;

c) the voltage at the output of the modulator;

d) a change in the frequency at the output of the transmitter.

A signal with a carrier frequency of F ₂ (F ₁ ), emitted by another moving object, enters the antenna and the signal input of the receiver mixer. A monochromatic frequency signal F ₁ (F ₂ ) is output to the mixer heterodyne input from the output of the frequency multiplier 6. The received pulse code information is displayed on the indicator.

The use of a device for extracting the envelope of pulses, a key circuit and a delay line compares the proposed transmitter of frequency-modulated signals from the specified prototype, since the distortion of the transmitted code pulse information is significantly reduced and the reliability of its reception is increased. Eliminating the deviation of the frequency of the opposite sign with respect to the useful deviation simplifies the construction of the receiver, since it does not require the installation of diode limiters at the output of the receiver discriminator and the fulfillment of special requirements for the intermediate frequency amplifier. The narrowing of the emission spectrum improves the compatibility conditions and noise immunity of the transmitter, as well as systems installed at the facility. The introduced new elements are simple in construction, but significantly improve the most important tactical and technical indicators of the transmitter of frequency-modulated signals.

Claims (1)

A frequency-modulated signal transmitter comprising an integrator, a phase modulator, a frequency multiplier, a power amplifier and an antenna, as well as a synchronizer and a modulator connected in series, the output of which is connected to another input of the power amplifier, and the other output of the synchronizer is connected to the input of the modulating signal source, while the output of the crystal oscillator is connected to another input of the phase modulator, and the integrator output is connected to the input of the discharge device, characterized in that, with In order to reduce distortion of information signals during transmission, between the output of the source of modulating signals and the input of the integrator a series-connected device for extracting the envelope of pulses and a key are introduced, while between the output of the source of the modulating signals and the input of the integrator an additionally introduced delay device is also included, and another input of the key is connected to the output discharge devices.

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