SU668063A1 - Selective frequency detector - Google Patents

Description

one

. The invention relates to radio technology and can be used in radio communications, in particular for controlling elements of an automatic frequency control (AFC) system of a receiver by a signal of a correspondent.

A frequency detector is known that contains two series-connected two-poles, one of which is a series-connected crystal oscillator and an inductor shunted by a diode detector, and the other consists of a balancing capacitor shunted by a second diode detector. An additional inductance coil is connected in series with the balancing capacitor.

However, this frequency discriminator does not have the noise immunity property when receiving frequency-modulated (FM) signals.

Also known frequency detector, built according to the scheme Travis.

. This type of frequency detector has insufficient noise immunity. If, in the receiver's passband, the amplitude in amplitude is comparable to or greater than the desired signal, then the AFC system, and, consequently, the entire receiver can be tuned to the interference frequency.

The closest technical solution to flaHHONjy invention. is a frequency discriminator containing two distorted circuits and two amplitude detectors with loads in the form of parallel-connected capacitors and resistors and two subtractive devices.

However, such a frequency detector does not have sufficient noise immunity.

The circuit of the invention is an increase in room stability when receiving FM signals.

The goal is achieved by the fact that two additional ultra-lowband filters tuned to the modulation frequency of the input signal are connected to the outputs of the diode detectors, and the outputs are connected to the inputs of different polarity detectors with a common load. FIG. 1 shows the functional cxeKia of the proposed selective frequency detector (SCHD); in fig. 2 is a statistical characteristic of the polarity variation of a constant control voltage when the sign of the frequency detuning at the output of the ACE changes. The selective frequency detector consists of two oscillatory circuits LjCf and LgCg disturbed with respect to the average frequency, connected in parallel to them through the diodes Dj and Dj, respectively, of capacitors Cj and C (and resistor R and R, which are respectively two diode detectors DjRjCjn. K They are connected to two narrowband filters, UPF, and UPF, associated respectively with two different-polarity detectors and with a total RJ load. The principle of operation of the proposed NRD is as follows:;; A complex PMFR report is received at the NRD input modulation (subcree) modulation (at the UPF and UPF2 inputs) this complex signal is transformed into an amp-frequency-modulated (AFM) signal. At resistors RI and Rg there are ampy-detector detectors is voltage: with the frequency of the modular speech and additional frequency, .. „- ...„ -.-,.,.,. „„, u1-deductions (tint). Using a low-frequency filter, a low-frequency signal (tint) is selected And through the diogv 5 R.I1) h is fed to the total load of the load, the result of HaiipsisceHiae is "knowledge of istekyl AFC control elements, GPI etbm effect noMexia: difference frequency Fn fg-lvi, groovy part. If the laser carrier frequency of the signal at the input of the device changes in the direction of increasing, then the electrical driving force (EDS) of the amplitude of the wave is amplified on the LjCi circuit. Than on the contour of LgC. & The 1 signal with the frequency of the additional modulation at the input of the UPF1 is also larger in amplitude than at the output of the UPF, since both

Claims (1)

This is because, in order to improve noise immunity when receiving FM signals, two additional narrow-filter filters tuned to the modulation frequency of the input signal are connected to the outputs of the diode detectors, and their outputs are connected to the input; multi-polar detectors with a total load. the filters are identical and have the same gain factors. The detected signal at the output of the diode D has a positive value, and at the output of the diode J) is negative. On the total load Rj, an algebraic addition of stresses occurs, in this case a positive voltage prevails, depending on the magnitude of the detuning (Fig. 2). If the frequency of the signal at the input of the device changes in the direction of decreasing, then with a larger amplitude there will be an emf on the circuit, therefore, a negative voltage prevails at the output of the NCC. (Fig. 2). In the absence of a detuning of the amplitude of the emf on the circuits LjCj and CC, are equal, and at the output of the device the voltage is zero. off , Uc- + I7c ИР, -V, Thus, thanks to the use of narrow-band filters and detectors with a common load - the robustness of the selection of the active frequency discriminator is reduced, and the probability of tuning the automatic frequency tuning system and the entire receiver is reduced, so as a sepa- rated frequency discriminator piearHpyeT only to the frequency of the zoopen module of the transmitter carrier. Claims of the Invention A selective frequency detector comprising two mutually disturbed resonant circuits connected to diode detectors, one or more of them.