SU766025A1 - Krolev's device for automatic tuning of frequency - Google Patents

Description

The invention relates to radio engineering and can be used in devices in which, after the termination of a continuously searching station, automatic correction of the tuning frequency of selective systems occurs.

A device for automatically adjusting the frequency, comprising series-connected high-frequency amplifier, mixer, intermediate-frequency amplifier, first amplitude limiter, frequency detector, first switch, first summing amplifier, the second input of which is supplied with voltage for tuning, the first correction circuit, the first reactive modulator and tunable local oscillator, the output of which is jg connected to the input of the mixer, as well as the second correction circuit and the second connected in series reactive modulator connected to the input of the frequency control efforts A high frequency 25 [1].

However, such a device has a small signal to noise ratio.

The purpose of the invention is to increase the signal-to-noise ratio. thirty

To do this, in a device for automatic frequency control, containing a series-connected high-frequency amplifier, a mixer, an intermediate-frequency amplifier, a first summing amplifier, the second input of which is supplied with a voltage for tuning, the first correction circuit, the first reactive modulator and a tunable local oscillator, the output of which is connected with the input of the mixer, as well as the second corrective circuit and the second reactive modulator connected in series to the amplifier frequency control input I high frequency, between the output of the high-frequency amplifier and the input of the second correction circuit, a second amplitude limiter, a second frequency detector, the control input of which is connected to the output of the first summing amplifier through a low-pass filter, a third correction circuit, and a third reactive modulator, are connected in series, second a switch and a second summing amplifier connected to another input with an output of a low-pass filter.

In FIG. 1 is a structural electrical diagram of the proposed device; in FIG. 2 - time diagrams. we.

The device contains a high-frequency amplifier 1, a mixer 2, an intermediate-frequency amplifier 3, amplitude 5 limiters 4 and 5, frequency detectors 6 and 7, switches 8 and 9, summing amplifiers 10 and 11, corrective circuits 12, 13 and 14, reactive modulators 15, 16 and 17, tunable local oscillator 18, low pass filter 19.

The device operates as follows.

At the initial moment of time, the voltage 15 (see Fig. 2, a) at the input of the summing amplifier 10 is minimal, and the switches 8 and 9 (see Fig. 2, c) are kept at a state of voltage at their control inputs, at where the 20 pi output of the frequency detector 6, the input of the summing amplifier 10 and the output of the frequency detector 7 - the input of the summing amplifier 11 are disconnected. The minimum voltage at the input of summing amplifier 10 corresponds to the minimum tuning frequencies of the selective systems of amplifier 1 (see Fig. 2, g), frequency detector 7 (see Fig. 2, f), as well as the minimum frequency of the output signal of the tunable local oscillator 18 (see Fig. 2, d). Increasing the voltage at the input of the summing amplifier 10, increase the tuning frequencies of the selective systems of the tunable local oscillator 18, amplifier 5, frequency detector 7.

When the frequency-modulated signal enters the passband of the direct path, the voltage at the input of the summing amplifier 40 ceases to change. By changing the voltage at the control inputs, the switches 8 and 9 are put into a state in which both loops of the automatic frequency control system turn out to be closed, and the process of entering the system in synchronism with the received signal. The tunable local oscillator 18 begins to track all changes in the frequency of the input signal. The signal of the frequency detector 6, in addition to the variable component, also contains a constant component proportional to the difference of the carrier frequency of the input signal converted in the mixer 2 and the tuning frequency of the frequency detector b (see Fig. 2.6) at the time the voltage at the input of the summing amplifier 10 ceases.

The summation of the constant components $ q of the output voltage of the frequency detector 6 and the voltage at the input of the summing amplifier 10 (it is assumed that it remains unchanged from the moment a signal of £ 5. L falls into the passband of the direct path of the automatic frequency adjustment system) allows us to refine the tuning frequency of selective systems of the amplifier 1 of the frequency detector 7 compared to that which was at the time preceding the switching of the switches 8 and 9. Since the filter 19 (see Fig. 2, e) clears the constant component acting Since the output of the summing amplifier 10, from the modulating function of the received signal, the tuning frequency of the selective system of the frequency detector 7 remains constant after the termination of transients, and the tunable frequency detector 7 behaves in the same way as a conventional frequency detector.

The presence of a second low-inertia circuit of automatic frequency adjustment makes it possible to reduce the delay time of the control signal, and hence, reduce the current detuning between the carrier frequency of the received signal and the tuning frequency of the selective amplifier system 1. Decreasing the detuning allows one to increase the signal-to-noise ratio at the output of the system direct path by narrowing the band the transmission of the selective amplifier system 1. Using a frequency detector 7 as a mismatch sensor allows you to create a system automatic frequency tuning, tunable in a wide range of frequencies.

Claims (1)

1. US patent 3784917, CL. 325-422, 1974 (prototype).