SU1497756A1 - Frequency telegraphy signal demodulator - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to improve noise immunity. The demodulator contains multipliers 1.4, low-pass filters 2.5, amplifier-limiter 3, phase shifter at ϕ / 2 11. The goal is achieved by introducing the detector 6 extreme samples, block 7 sample-storage, algebraic adder 8, integrator 9, adjustable rms 10, low pass filter 12, reference voltage source 13, switch 14 and amplitude comparator 15. When choosing equal values ΔW _o = ΔW _s (due to an automatic control loop formed through the integrator 9), the frequency of r-10 traces changes carrier frequency oscillation of the demodulator input signal. At the same time, there is no effect of manipulating the frequency of the input signal of the frequency telegraphy of the demodulator on the process of adjusting the frequency of Mr. 10. 1 sludge.

Description

3149

The invention relates to radio engineering and can be used in receivers of signals of frequency telegraphy.

The purpose of the invention is to increase the noise immunity of the demodulator.

The drawing shows a structural electrical circuit of the demodulator which is assumed.

The demodulator contains the first multiplier 1, the first low-pass filter 2, the amplifier-limiter 3, the second multiplier A, the second low-pass filter 5, the extreme samples detector 6, the sampling-storage unit 7, the algebraic adder 8, the integrator 9, the adjustable generator 1Q, phase shifter on P, the third filter 12 lower frequencies, the source 13 of the reference voltage, the switch 14 and the amplitude comparator 15

The demodulator works as follows.

In multipliers I and 4, as well as in the first 2 and second 5 low-pass filters (LPF), the quadrature components of the demodulator input signal are extracted at the frequency

UCAJ QC - С3 „g,

where QJJ is the instantaneous frequency of the demodulator input signal;

COpf is the oscillation frequency of the adjustable oscillator 10. The bandwidths of the first 2 and second 5 LPFs with steep slopes of amplitude-frequency characteristics (PM) are chosen based on the width of the input signal spectrum of the demodule, the torus, and taking into account the instability of its frequency and oscillation frequency generator 10

The detector of 6 extreme samples records the moments of time corresponding to the intersections of zero

positive derivative

output signal of the second low pass filter 5 and generates short pulses corresponding to the temporal position of the extreme counters of the output signal of the third low pass filter 12. Amp limiter 3 stabilizes the amplitude of the signal from the output of the first low pass filter 2 at the level U ,, made, for example, in the form of a CS chain, is determined only by the ratio of the value of L CO and its cut-off frequency, which is chosen substantially less than the cut-off frequencies of the first 2 and second 5 LPF.

In block 7 of sample-storage, the amplitude of the output signal of the third low-pass filter 12o is synchronously detected. The polarity of the voltage at the output of block 7 of the sample-storage is determined by the sign of the value of SALW SO - EF (, rtrc depends on the parcel of the input PT signal The instantaneous demodulator input frequency is

Ut "с + с" - bWc, where Ссо the value of the frequency of the carrier oscillation of the input signal of the demodulator;

LsO- its frequency offset under

the effect of frequency manipulation;

ot +1 or ot -1 - characters of the transmitted message

The amplitude comparator 15 evaluates the symbols of the transmitted message in accordance with the polarity of the output voltage of the sampling-storage unit 7.

The voltage from the output of the source 13 of the reference voltage is selected, for example, equal to Ug and, / 2. The polarity of this voltage at the output of the polarity switch 14 (due to its control by the output signal of the amplitude comparator 15) is set to the corresponding polarity of the output signal of the sampling-storage unit 7, resulting in any sprinkling of the demodulator input signal (оС or ot -l) ) the polarity and voltage level at the output of the algebraic adder 8 corresponds to the direction and degree of deviation of the & G3 from the value of AU ,, selected on the slope of the frequency response of the third low-pass filter 12 and corresponding to the exclusion of voltages. With UCOg & (0 (, what is achieved due to the loop of automatic regulation formed through the integrator 9), the frequency of the adjustable oscillator 10 tracks the change in the frequency of the carrier oscillation of the input signal of the demodulator, as a result of which the CoPo – P equation is absent

the effect of manipulating the frequency of the demodulator CT input signal on the frequency control process with a tunable oscillator 10,

The demodulated symbols of the transmitted message, corresponding to the manipulation of the frequency of the input PT signal, from the output of the amplitude comparator 15 are fed to the output of the demodulator.

Claims (1)

Invention Formula A demodulator of frequency telegraphy signals containing an amplifier-limiter, whose input is connected to the output of the first low-pass filter, whose input is connected to the output of the first multiplier, the first input of which is connected to the output of the phase shifter to the / 2f input which is connected to the first input of the second transmixtel, whose output connected to the input of the second low-pass filter, wherein the second input of the first multiplier is connected to the second input of the second multiplier and is the input of the demodulator, characterized in that Accelerating noise immunity, it a third low-pass filter, a sample-storage unit, an extreme sample detector, amplitude comparator, adjustable oscillator, integrator, algebraic adder, switch and reference voltage source, whose output is connected to the first input of the switch, the second input is connected to the output of the amplitude comparator, are introduced, the first input of which is connected to the output of the sampling-storage unit and to the first input of the algebraic adder, the output of which is through a serially connected integrator and a tunable generator The torus is connected to the first input of the second multiplier, the output of the second low-pass filter is connected to the first input of the sampling-storage unit through a detector of extreme samples, the second input of which is connected to the output of the third low-pass filter whose input is connected to the output of the limit amplifier, and the output of the switch is connected with the second input of the algebraic adder, the second input of the amplitude comparator is connected to the zero potential bus, and the output of the amplitude comparator is the output of the demodulator.