SU1275318A1 - Frequency meter - Google Patents

Description

element 2I-or 19 allows the significant phase discrimination in the looped area to increase the meter accuracy by increasing the sensitivity

1275318

phase transition through the zero level. 1 il.

The invention relates to a radio measuring technique and can be used to automatically measure the frequency of a radio signal in a wide range of frequencies with high accuracy. The aim of the invention is to improve the accuracy of measuring the frequency of a radio signal over a wide frequency range. The drawing shows a block diagram of the meter. Laser 1, four-quarter-waves are successively located on the same optical axis; plate 2, optical quadrature capacitor 3, optical analyzer 4, system forms; their lenses 5 And N-branch optical line 6 delay. The source 7 of the signal under study is electrically connected to one of the pairs of plates of the Quadrature capacitor 3 directly, and to the other pair through a phase shifter 8. Each of the N phase discriminators 9 has two pairs of coplanar photodetectors 10, 11 and 12, 13, the outputs of which are electrically connected with inputs of subtractors 14 and 15 respectively. Output of subtractors 14 is connected to the signal inputs of threshold devices 16 and 17, output of the subtractors 15 with the signal input of threshold devices 18. Threshold outputs devices 16 and 18 are connected respectively to the first inputs of the first and second elements AND the logical element 2I-IL 19, which is the output device of the phase dis. the criminator 9, and the output of the threshold device 17 is connected to the second input of the first element I and to the second inverting input of the second element AND element 2I-OR 19. The output of each of the N phase discriminator 9 is optically coupled with the corresponding pair of optical fiber 6 through the forming lenses 20 delays, and the output is electrically connected to the corresponding register bit 21, the frequency meter works as follows: “A narrow coherent light beam with linear polarization generated by laser 1 passes through the L / A plate 2, where melts circular polarization and lays on the optical input of the quadrature capacitor 3. The electrical signal under study is fed to the electrical input of the optical quadrature capacitor 3, and to one pair of opposite plates directly, and to the other pair via the phase shifter 8. Since the phase shift is set by the phase shifter 8 constant (90), a circular simulating field is formed in the volume of the crystal of the optical quadrature capacitor 3, which shifts the frequency of the light wave oJ by the magnitude of the frequency studied for LO signal. Thus, at the optical output of the quadrature capacitor 3, the light wave has a frequency c. and circular polarization. Passing through the optical analyzer 4, the polarization of the light wave is converted to linear. Further, a system of forming lenses 5 forms a flat coherent light beam with a uniform intensity across the section. The pad is coaxially into the end section of the optical delay line 6, the light beam is divided evenly and with the same initial phases into K 2N parts (i.e., K 2N optical fiber & in the beam). The accuracy of the separation is determined by the accuracy of the fabrication of the optical fibers. The optical lines of the optical line 6 of the excitations are divided into pairs so that in each pair the spatial delay of one light beam (measuring) relative to the other (reference) is provided. The light rays from the two light guides of each pair through the forming lenses 20, with giving flat light rays, fall on the coplanar photodetectors 1013 at a given angle. As a result of the interference of the measuring and reference light rays in the plane where the photodetectors 10–13, each phase discriminator 9, are located, an interfering pattern of alternating dark and light bands parallel to the photodetector aperture occurs. The position of the light and dark bands of the interference pattern with respect to the apertures of the photodetector 10-13 depends on the phase difference between the oscillations of the measuring and reference light rays in each i-th pair of optical fibers connected through forming lenses 20 with the i-M phase discriminator. The phase difference between the oscillations of the reference and measuring channels in the i-th pair of optical fibers is proportional to the difference in the lengths of the optical fibers of the pair dT | tj is l 2 d1 (uf is the difference of the lengths of the optical paths for the 1st pair of optical fibers) and is equal to -t -r 1 lU, L is the speed of light in the fiber; circular frequency of the laser; circular frequency radio signal. When the frequency of the radio signal changes and the phase difference of the light oscillations in each i-th fiber pair is changed by different values. Accordingly, the interference patterns appearing on the photodetectors of various phase discriminators are shifted to different numbers of periods. 9, and the count is a multiple of degree two. Phase discriminators 9 fix the shift between the light oscillations of the measuring and reference light rays of the corresponding pair of optical fibers and convert it into a logical O, if the sign of U is perfect. negative, and in logical 1 if the sign and, - cos uV is positive. 55 Frequency count heterogeneity, due to the fact that the cos function is periodic, is eliminated by the introduction of additional recording channels, in which the spatial delay of 4 G is used. The length of the second (measuring) fiber of the i-th pair is determined by the expression 1,. Such a series of spatial delays allows determining the frequency of the radio signal in the form of h-S, -, - h in the recording device. 1, at cos (r-e) 0; (f: -f) 0; uj. g4, afj 2 is the frequency of the laser light wave. In register 21, the received sequence of logical O and 1 all channels of the recording device is memorized at each time instant. This binary code corresponds to the frequency of the radio signal under study, Phase discriminator 9 operates as follows. The photodetector current is proportional to the intensity of the light flux falling on it. The distance between the photoreceivers of each pair 10, 11, and 12, 13 is chosen equal to half the period of the interference pattern, which means that if one of the photoreceivers of each pair is located at the maximum of illumination, then the second is at the minimum of illumination. The currents of the photodetectors 10 and 11 of the first pair are fed to the inputs of the subtractive device 14, and the currents of the photodetectors of the second pair 12 and 13 are fed to the inputs of the subtractive device 15. The subtractive devices 14 and 15 suppress the background light of the photodetectors and are proportional to the intensity maxima and minima of interest bands. The first pair of photodetectors 10 and 11 is the basis, the second pair 12 13 is an additional pair and is put into operation at that moment, 1 (when light of the same intensity strikes the main pair of photodetectors 10 and 11, which is equivalent to a phase transition

S1

characteristics of the discriminator through the zero level.

At first 16 to third 18 threshold. the device has a zero threshold, and the second threshold device 17 has a trigger threshold different to the insensitivity voltage of the first threshold device 16. The signal inputs of the threshold devices 16 and 17 are given a signal from the output of the first subtractive device 14, and the signal input of the third threshold device 18 is signal from the output of the second subtractive device 15 "

If the position of the light and dark bands of the interference pattern on the photodetectors 10 and 11 is such that the illumination kx is significantly different, then it is more intense. at the output of the subtracting device 14 is greater than the threshold voltage of the threshold at the second threshold device 17 and the voltage at its output corresponds to the logic level 1. The voltage from the output of the second threshold device. 17, post na on. element 2I-1-SHI 19 opens the first logical element AND and closes the second element I. In this case, the output of logic element 2И-OR will have a voltage corresponding to the logic level of the first threshold device 16, Level 0 or 1 from the output of element 2И-OR 19 enters the corresponding:, common bit input of the register 21 and sets it to the position corresponding to 0 or 1, depending on the state of the first threshold device 16.

If the position of the light and dark stripes of the interference pattern is that of the KOBOs, that the heating of the first pair of photodetectors 10 and 11 is the same. or the difference between them is less than the trigger voltage of the second threshold device, then the threshold device 17 is set to the position corresponding to the logical one, and consequently, for. the first element AND is hidden and the second element AND the logical

element 2i-or. As a result, the output of the logic element 2I-Shta 19 enters the logic level. That corresponds to the output level of the third. threshold device 18, in; which is in a state of logical O or 1, depending on which

186

12 or 13 of the second pair of photo-receivers are more lighted. Since the photoreceivers 12 and 13 of the second pair are shifted relative to the photoreceivers of the first pair 10 and 11 by a quarter of the period of the interference pattern, then equal or close illumination of the photoreceivers 10 and 11 of the first pair corresponds to the maximum difference in the brightness of the photodetectors 12 and 13 of the second pair, in this case, the threshold device 18 triggered and there is no uncertainty in the output signal. Phase discriminator due to the final sensitivity of the phase discriminator.

The proposed construction and algorithm of operation of the phase discriminator 9 makes it possible to increase its sensitivity in: the part of the phase transition through the zero ypoBeHJi k., As a consequence, the accuracy of the frequency meter, since the error is due to inaccurate; (especially in the higher-resolution recording devices), it causes a large error in from /. ,: frequency

The expression for frequency measurement accuracy is

-SP + y

where n is the number of light waves placed on the spatial difference in the path of the rays in the measuring and reference optical fibers of the pair dT. Using a laser with a wavelength of f 0.63 μm, the device is provided with a frequency of the investigated signal ic 500 MHz ((0.6 m) at 0.6 m and a maximum accuracy of ci (.) 2-10, which greatly exceeds the accuracy of traditional radio frequency measurements.

Claims (1)

Invention Formula The frequency meter containing the source of the signal under study, the N-OT delay line and the N-channel recording device, in each i-OM channel of which a phase discriminator is connected, the output of which is connected to the iM bit input of the register and with that. In order to improve the accuracy of frequency measurement, a laser, a quarter-wave plate, an optical quadrature capacitor, an optical analyzer, a system of forming lenses optically connected with an N-branch delay line, made in the form of a fiber branch of a light beam with N pairs of optical fibers, the outputs of the i-th pair of optical fibers through the forming lenses are optically coupled to the i-th phase discriminator, the phase discriminator is made in the form of two pairs of coplanar receivers, the distance between which is in a pair of half the period of the interference pattern, and the distance between the extreme photodetectors of pairs is equal to a quarter of the periods of the interference pattern, the outputs of each pair of photodetectors are connected respectively to the inputs of the first and second detractors, the output of the first subtracter is connected to the signal inputs of the first and second threshold devices, the output of the second subtractive device is connected to the signal input of the third threshold device, the outputs of the first and third Each of the threshold devices are connected respectively to the first inputs of the first and second elements AND element 2И-OR, and the output of the second threshold. device is connected to the second input of the first element AND and the second inverting input of the second element AND logic element 2И-OR, the output of element 2И-OR is the input of the discriminator phase, and the threshold of the second threshold device is higher than the thresholds of the first and third threshold devices by the voltage value the insensitivity of the first and third threshold devices, and the source of the signal under study is connected to one of the pairs of opposite plates of the optical quadrature capacitor successively, and to the second pair through a phase shifter.