SU849528A1 - Frequency-shift keying signal demodulator - Google Patents

Description

one . The invention relates to radio engineering and can be used in noise-resistant radio receivers of discrete signals of communication systems and telemetry.

A demodulator of frequency telegraphy signals is known, containing serially connected impulse-phase detectors, a memory unit, a low-frequency equalizer, a tunable oscillator, a shaper of short pulses and. the electronic key, the output of which is connected to the first input of the pulse-phase detector, while the second output of the memory unit is connected to the input of the telegraph signal generator via the manipulation filter

However, the known demodulator has a low noise immunity. The circuit of the invention is an increase in noise immunity.

For this, the demodulator of the signals of frequency telegraphy, containing

serially connected pulse-phase detector, memory block; a low-frequency corrector, a trimming generator, a short pulse shaper, and an electronic key whose output is connected to the first input of a pulse-phase deTK, while the second output of the memory unit is connected to the input of a telegraph signal generator through the manipulation filter, and limiting amplifier, frequency discriminator, phase inverter, second Schmidt trigger and element OR,

15 to the second input of which the output of the first IIDt trigger is connected, the input of which is connected to the output of the frequency discriminator, the input of the amplifier - limiter is connected to the second input of the pulse-phase detector, and the output of the OR element is connected to the second input of the electronic key.

The drawing shows a structural - electrical circuit of the proposed demodulator,

The demodulator of the frequency telegraphy signals contains a pulse-phase detector 1, memory block 2, low-frequency equalizer 3, adjustable oscillator 4, shaper 5 short pulses, electronic key 6, limit amplifier 7, frequency discriminator 8, first and second Schmidt trigger 9 and 10, respectively, a phase inverter 11, an OR element 12, a manipulation filter 13, a telegraph shaper 14.

The demodulator works as follows.

The received mixture of signal and noise is gated in a pulse-phase detector 1 by a pulse signal formed from the voltage of a tunable oscillator 4, with the electron beam 6 open, the frequency of the tunable oscillator 4 is control-. It is powered by a voltage pulse phase detector 1 that has passed through memory block 2 and a low frequency equalizer 3, which has a high inertia near zero frequency and is inertial in the region of modulating frequencies. Such a modified first order phase locked loop (PLL) with a small spacing of the manipulated frequencies (equal to 0.7 from the speed of the manipulation) and in the absence of a phase discontinuity during manipulation provides a high interference immunity of reception with an instability of the average received frequency. However, when exposed to noise, the noise and the received signal form a resultant oscillation, the frequency of which varies both as a result of manipulation, to and from noise. In this case, the greatest danger is represented by rapid frequency deviations, which have a large amplitude and are directed to the boundary of the synchronism region, since such bursts lead to disruption of tracking and ultimately to errors in signal reception (c6onJ), due to the presence of manipulation in the received signal in each clock interval due to the shift of the instantaneous frequency from the average value to one or another side (depending on the sign of the received signal, one of the limits of the synchronism region

approximated, and the friend is removed from the received frequency value. Due to the random nature of noise imposing on a signal, the most dangerous, resulting in a failure, are those frequency deviations that are directed toward the near edge of the sync band.

Frequency discriminator 8 connected to the analog input of the pulse-phase detector 1 via the limiting amplifier 7 is used to detect dangerous and tracking changes of the instantaneous frequency leading to failure of the instantaneous frequency, which is connected to the analog input of the pulse-phase detector 1 via the limiter 7. Signal amplitude at the output of the partial discriminator 8, the first and second Schmidt triggers 9 and 10 are analyzed, the thresholds of which are shifted so that their operation occurs when the instantaneous frequency exceeds 1.52 times the value of one third-party frequency deviation caused by manipulation. If there are transistors with one type of conductivity and an identical circuit of the Idsdt trigger, the second one is connected to the frequency discriminator 8 through the phase inverter I1. The pulses of Schmidt triggers through the element OR 12 control the electronic key 6, stopping the supply of gating pulses for a time exceeding the allowable upper and lower limits of frequency deviations and a mixture of the input signal and noise. Thus, tracking failures in the PLL system are eliminated by fixing the synchronous-phase demodulator. (The SFD in the state it was in before the anomalous frequency burst arrived before the end of this burst in the wideband input path. The processes in the SFD path and in the anomalous burst detection device are almost matched in time due to the absence of narrow-band filter circuits.

Thus, in the proposed demodulator, noise immunity is increased by quite simple means. Setting up the circuit does not require complex test instrumentation and a lot of labor during adjustment.

Claims (1)

1. Date of Great Britain No. 951230, H 3 A, 1-964 (prototype). / g - YU 7 / /four