SU60701A1 - Device for receiving high-frequency oscillations modulated by frequency - Google Patents

Description

As is known, when receiving signals modulated in frequency, the effect of suppressing noise increases when there is an amplitude limiter in the high (or intermediate) frequency of the receiver.

Existing limiter circuits are usually complex and require additional amplification and complexity circuits in the receiver.

The proposed method of limiting the amplitude of the high frequency is free from the listed drawbacks, requires the use of only one lamp and creates an effective limitation of the amplitude with simultaneous significant amplification. The essence of the method is the use of a local oscillator operating in the capture mode by the incoming signal.

In the present invention, for the purpose of limiting, the circumstance is used that the amplitude of oscillations generated by the local oscillator operating in the capture mode does not depend on the amplitude of the exciting oscillations.

FIG. 1 gives the scheme for the implementation of the proposed method; in fig. 2 is a diagram of the dependence of the oscillation frequency of the local oscillator operating in the capture mode on the frequency variations of the exciting

fluctuations; in fig. 3 is a block diagram of a VHF receiver including the present invention.

FIG. I index / denotes the input part of the receiver containing the high frequency amplifier, the 1st detector, the local oscillator and the intermediate frequency amplifier.

From the output of the intermediate frequency silicon, oscillations are supplied to a series circuit containing capacitance 2 and variable resistance 3. The voltage taken from resistance 5 is fed to the signal grid of a complex lamp 4, which can be taken as a 6A8 or 6L7 lamp. Oscillations obtained in the anode circuit 5, clamped by the stabilizing diode 6, will be limited in amplitude and amplified compared to the oscillations obtained at the output of the intermediate frequency amplifier. Further, oscillations are supplied to a demodulator of frequency-modulated signals 7, for which any type of demodulator can be used. After demodulation, the signals are fed to a low frequency amplifier 8.

The oscillation frequency of the local oscillator operating in the capture mode will follow the frequency variation of the exciting oscillations according to the law graphically depicted

2С5

in fig. 2. When selecting an appropriate capture bandwidth, oscillations at the output of the local oscillator will be modulated in frequency according to the same law as oscillations of the signal applied to the input. Thus, the components of the signal expressing the frequency modulation will pass through the described device, and the components expressing the amplitude modulation will not pass, and this results in an effective operation of the limiter.

The proposed device gives an additional positive result in the fight against interference when receiving signals modulated in frequency. This is achieved by the fact that the circuits preceding the heterodyne circuits are upset about the carrier frequency of the received signal. Provided that the natural frequency of these circuits is outside the capture band of the limiting local oscillator, the carrier frequency of the oscillations created by the impulse noise will also lie outside the capture band. This will lead to a significantly smaller effect of the interference on the local oscillator frequency, since the pulse interference excites the loop at its resonant frequency. Thus, an additional gain is obtained in the fight against interference with. receiving frequency-modulated signals.

The advantages noted above are especially great when receiving VHF signals. As is known, the VHF receiver in its present form is rather complicated.

The proposed device can be a very efficient ultra-high frequency vibration amplifier and the VHF receiver is greatly simplified. FIG. 3 is a diagram of such a device. Here, oscillations from the antenna are supplied to circuit 9, tuned to the frequency of the received signal modulated in frequency. The oscillations obtained in contour I are then used to synchronize oscillations generated by the local oscillator 10. As already indicated, oscillations of the same frequency, but amplified in amplitude, will arise in the contour.

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At this, their amplitude is constant and does not depend on the amplitude of oscillations at the input. Further, the oscillations are applied to the demodulator Y /, the circuit of which can be any. After demodulation, the oscillations are fed to the input of the low frequency amplifier 12 and can be used accordingly.

When it is required to capture a local oscillator with even smaller voltages (for example, in cases where the transmitter frequency deviations have large limits, which entails an expansion of the capture band, etc.), it is necessary to reduce the amplitude of oscillatory excitation of the local oscillator. This leads to a decrease in the voltage arising at the output of the local oscillator, i.e., a decrease in the gain coefficient of such a local oscillator amplifier. In this case, one more cascade of the local oscillator amplifier can be used, and the oscillations obtained at the output of the first local oscillator can capture the second local oscillator. With the presence of such a two-stage amplifier, the amplification factor of the oscillations of the VHF can practically reach a value of 100–200 thousand with a fairly wide capture band.

The proposed method for receiving VHF signals can be combined with the method of euperheterodyne reception, i.e., the oscillations obtained at the output of the local oscillator amplifier can then be converted to the normalized frequency by the usual method.

Subject invention

Claims (3)

1. A device for receiving high-frequency oscillations that are frequency modulated, using a local oscillator to amplify these oscillations, which is in synchronization with the received signal, characterized in that, in order to limit the oscillation amplitude, a stabilizing diode is connected parallel to the oscillator circuit. 2. The form of the device pop. 1, characterized in that the regulation of the power factor} is carried out by changing the magnitude of the negative bias applied to the diode anode. 3. The form of the device according to paragraphs. 1 and 2, characterized in that, for the purpose of increasing, 1 "signal-to-noise at the output in the circuits preceding the local oscillator is referred to as p), the contours are referred to as detuned relative to the carrier frequency of the received signal. / gett I fnsc Strip zahbat. f capture d