SU1228027A1 - Apparatus for measuring frequency of signal sprectrum power centre of gravity - Google Patents

Abstract

The invention can be used in various types of α-radio engineering installations. The purpose of the invention is to improve the accuracy of frequency measurement. The device contains a mixer 1, 4ltr 2 low frequencies, an amplitude detector 3, a block 4 comparing the amplitudes, a switch 5, controlled local oscillators 6 and 7, a synchronizer 8 and a block 9 of registration. The introduction of a controlled local oscillator 7, a synchronizer 8, and a switch 5 into the device will allow automatic setting of the frequencies of the two local oscillators symmetrically to the signal spectrum. 3 il. (L p | / e /

Description

The invention relates to a radio metering technique and is intended for use in radio engineering installations for various purposes.

The purpose of the invention is to increase the frequency measurement accuracy by automatically setting the frequencies of two local oscillators symmetrically to the signal spectrum.

Fig, 1 shows a structural diagram of the proposed device; in fig. 2 and 3 - signal plots,

The device comprises a mixer 1, a low-pass filter 2, an amplitude detector 3, an amplitude comparison unit 4, a switch 5, two controllable heterodynamic 6 and 7, a synchronizer 8 and a recording unit 9.

The first input of mixer 1 is the input of the device, the output of mixer 1 is connected through a serially connected low-pass filter 2 and the amplitude detector 3 is connected to the first input of the amplitude comparison unit 4, the output of which is connected to the controlled local oscillator 6 and 7, the output of the local oscillator 6 7 are connected respectively to the first and second inputs of the switch 5, the output of which is connected to the second input of the mixer 1, the output of the synchronizer 8 is connected to the third input of the switch 5 and the second input of the amplitude comparison unit 4, the inputs of the registration block 9 connected to the outputs of the local oscillators 6 and 7.

The device works as follows.

The spectrum of the input signal in the mixer 1 is converted in frequency by the local oscillators 6 and 7. The frequencies of the controlled local oscillators are chosen so that the frequency of the controlled local oscillator 6 is lower than the frequency of the input signal, and the frequency of the controlled local oscillator 7 is higher than it, f, f. ffj ft + fnp (where f,, f, are the frequencies of controlled transmitters 6 and 7; D. is the intermediate frequency of the signal after conversion (r 2a). In one of the switch positions, the input signal is converted by frequency using a controlled local oscillator 6. At the same time, the spectrum of the signal at the mixer output repeats the spectrum of the input signal (4ig. 26). In another position of the switch, the input signal is converted using a controlled local oscillator 7. At the same time, the spectrum of the signal at you

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the course of the mixer is inverted relative to the spectrum of the input signal (figv), i.e. the upper and lower sidebands are interchanged with respect to the input spectrum. Then, using a low-pass filter 2, whose cut-off frequency is equal to the intermediate frequency of the signal at the mixer output (Fig. 2d), the corresponding part of the signal spectrum is selected at each switch position: low-frequency and high-frequency (hatching in Fig. 26c). Then, the amplitude of the signal at the filter of the low pass filter 2 is selected by the amplitude detector 3. The obtained amplitudes of the signals arrive at block 4 of the amplitude comparison. Amplitude comparison unit 4 is a repeater with a variable gain symbol with a smoothing filter at the output. The operation of the amplitude comparison unit 4 and the switch 5 is synchronized by the synchronizer signal 8, which is a conventional square wave generator. The voltage plot at the repeater output is shown in FIG. 3. As a result of smoothing, at the output of the amplitude comparison unit 4, we have a constant voltage, the magnitude and sign of which correspond to the magnitude and sign of the frequency detuning of the input signal relative to the transient frequency of the discriminator. This error voltage from the output of the amplitude comparison unit 4 is fed to the controlled heterodyne 6 and 7 to adjust their frequencies. Controlled local oscillators 6 and 7 are designed in such a way that a positive control voltage increases the frequency of the local oscillators, and a negative one reduces it. Recording unit 9 is two frequency meters that measure the frequencies of the local oscillators 6 and 7. The value of the signal frequency corresponds to the half-sum of the measured frequencies of the local oscillators. If the input spectrum is symmetrical, this device will measure the center frequency of the input signal.

Using a single frequency crossover filter eliminates the effect of its characteristics on accuracy; measuring the frequency of the input signal, since possible instabilities are equally manifested when both the low-frequency part of the signal spectrum and the high-frequency part are detected; the transitional frequency of the discriminatory characteristic is equal to the intermediate frequency ". and does not depend on temperature fluctuations of the filter characteristics. The stability of the transitional frequency is determined by the frequency stability of the controlled local oscillators.

Claims (1)

Invention Formula A device for measuring the frequency of the energy center of the signal spectrum plate, containing a mixer, the first input of which is the device input, a low-pass filter whose input is connected to the mixer output, and the output through the amplitude detector to the first input of the amplitude comparison unit whose code is connected to . the input of the controlled local oscillator, and the register unit, the input of which is connected to the output of the controlled local oscillator, characterized in that, in order to improve the accuracy of frequency measurement, it is equipped with a second controlled local oscillator, synchronizer and switch, the output of which is connected to the second input mixer, and the first and second inputs, respectively, with the outputs of the first and second controlled local oscillators, the output of the synchronizer with the third input of the switch and the second input of the amplitude comparison unit, the output of the latter connected to the input Lravl emogo of the second local oscillator and a second input of the recording unit - with the output of the second local oscillator. four // 7р г