SU932426A1 - Device for measuring four-terminal network frequency characteristics - Google Patents

Description

 The invention relates to electrical measurements, in particular to measurements of four-pole NIKOV characteristics, and can be used to measure the frequency response of a delay time (e.g., phase delay time) of delay lines, filters, communication channels and other circuits. A device for measuring the phase-frequency characteristic is known, which contains an oscillator with a variable frequency, to the output of which there are connected reference and measuring channels, each of which contains a unit for selecting reference moments (the measured quadrupole is included in the measuring channel), and a raster indicator, a horizontal scanner unit of which is associated with an oscillator. Signal frequency converters are included in the reference channel and in the measuring channel after the measured quadrupole. The device has a phase detector, which is a phase shift converter between signals with a converted (constant) frequency to a voltage. The phase detector contains units for detecting phase shift reference points. A raster indicator input is connected to the output of the phase detector. The indicator brightness control input is connected to the control unit. On the screen of the indicator, the phase-frequency characteristic of the measured quadrupole l is observed. The drawback of the device is a relatively large measurement error, which is a consequence of the use of intermediate operations with signals: frequency conversion and phase shift conversion to voltage. In addition, when reading an oscilloscope from the screen, an error occurs due to geometric distortions and instability of the image of the measured characteristic relative to the scale printed on the screen. The unambiguous measurement range of the phase shift from –18 ° to + l80 or 0–3.6b is insufficient for many measurable circuits, such as delay lines. To convert the phase response to the frequency response of the phase delay time, an additional calculation is needed, which increases the measurement time. The closest in technical essence and the achieved result to the proposed is a device for measuring the frequency characteristic of a quadrupole, containing a variable frequency generator, connected to the inputs of the sample and investigated quadrupoles, the outputs of which are connected to the corresponding inputs of the phase detector, the output of which is connected to the unit the selection of P points, the outputs of which are connected respectively to the input of the control unit pkbst | 6 raster indicator and to the input of the vertical scan indicator Erez serially connected voltage generator and the stepped delay lU1Niyu, a modulator whose output is connected to the generator and the input of the horizontal scanner t 1Nedostatkom known apparatus is large the measurement resolution is equal to L80 °. When measuring circuits with a phase shift of, a small number of periods the phase-frequency characteristic will be represented by a small number of points. Therefore, the measurement error of intermediate values (by interpolation) can be very large. On the screen, the indicator is set; The properties of the quadrupole under study are induced by the frequency characteristics; therefore, additional calculation is required to measure the phase delay time of the quadrupole, which increases the measurement time. The purpose of the invention is to reduce the measurement error and increase the speed when measuring the frequency response of the phase delay time. The goal is achieved by

Claims (2)

that in the device for measuring the frequency characteristics of the quadrupole, containing a generator of changing output /: block 9, which is the output of reference channel 2, is directly connected to the input of block 13 of vertical frequency, connected to the inputs of the reference and test quadrupole, raster indicator, output of the test quadrupole through the first block of selection of moments of reference is connected to the input of the control unit of brightness of the raster indicator, the output of the exemplary quadrupole through the second block of moment selection reference input is connected to the vertical scanning of the raster display unit, the horizontal scanning unit KOTOjsoro connected to sync generator block .... 1 is a block diagram of the proposed device; Fig. 2 are time diagrams for the operation of the device. The device for measuring the frequency response of the quadrupole comprises a radio pulse generator 1 with a carrier frequency varying with. as the pulses arrive. The output of the generator 1 is connected to the reference channel 2 and the measuring channel 3. The latter includes the measured quadrupole 4, the output of which through the matching and amplifying stages 5 is connected to the input of the block 6 for the selection of the moments of the delay time. The reference channel 2 includes an exemplary quadrupole 7, the output of which is connected through the matching and amplifying stages 8 to the input of the block 9 for the selection of the moments of the countdown of the delay time. Each of blocks 6 and 9 contains discriminators of counting and counting levels connected to an input of the device, a distributor and a valve. The output of the counting discriminator is connected to the input of the distributor, to one of the outputs of which the input of the valve is connected. The second input of the valve is connected to the output of the discriminator of the reference level. The output; the valve is the output of blocks 6 and 9.. In the device for measuring the frequency response, a raster indicator 10 is used, which comprises a cathode ray tube 11, a brightness control unit 12, a vertical scanning unit 13 and a horizontal scanning unit 14. of the raster indicator 10. The output of block 6, which is the output of measuring channel 3, is directly connected to the input of block 12 of controlling the brightness of indicator 1; Block C of the horizontal scan is connected to the synchronization unit of generator 1. The device operates as follows. When measuring the frequency response of the phase time delay, radio pulses (Fig.) From the oscillator 1 are fed into the reference 2 and into the measuring 3 channels. In radio pulses from the outputs of the reference (fig. A) and measured (fig.2jb) quadrupole 7 and 4, passed through the corresponding matching and amplifying stages 8 and 5, select the reference times in the form of pulses (Fig.2, s, 3) . The moments of reference are extracted using blocks 9 and 6. For this purpose, in each of blocks 9 and 6, the discriminator of the counting level is used to generate pulses corresponding to the instant of the signal crossing the specified counting level in a specific direction. These pulses come to the input of the distributor. The signal from the distributor output corresponding to the specified number of the moment of intersection of the counting level opens the valve. One valve passes through the gate, the pulse from the output of the discriminator is a countdown, which pulses the moments of intersection of a signal of a given countdown level of the phase delay (zero level) in the form of pulses. The counting level is set higher than the maximum interference level. The number of the moment of intersection of the counting level is set in such a way that the counting interval is located on the site where the transient process in the signal decays to a sufficiently small value. The distributor in each of blocks 6 and 9 is set to its initial state before the arrival of the next radio pulse from the output of the corresponding 5- or 8 cascades. The pulses from the output of the reference channel 2 synchronize the vertical scan of the indicator 10. The pulses from the output of the measuring channel 3 control the brightness indicator 10. Horizontal sweep (Fig. 2.1) indicator 10 is carried out in accordance with the law of change of the carrier frequency of radio pulses (Fig. a) and synchronized from generator 1. On the screen of the cathode ray tube 11, The frequency response of the phase time delay (Fig.) of the measured quadrupole Q relative to the exemplary quadrupole 7 is combined with points. To reduce the measurement error on the screen of the cathode ray tube 11, a scale can be formed on the screen of the measured beam (scale grid. For this The brightness control signal of the indicator 10 is mixed with pulses from the generators of the calibration signals. The image of the measured characteristic and scale on the screen can be Positive and negative. When measuring the phase time delay, less than the minimum period of oscillation of the carrier frequency, the inputs of the reference and measuring channels 2 and 3 can be fed from the generator 1 to continuous oscillations with varying frequency, and not radio pulses. In this case, each of blocks 6 and 9 contains only the discriminator of the reference level (zero level). With a sufficiently large number of points on the screen (FIG. 2, §), the horizontal scan signal (f, ig.2, {) may not be stepped, but, for example, sawtooth. It is possible to synchronize the change in the oscillation frequency of the generator 1 from the horizontal scanning unit or to synchronize the block from the generator 1. When measuring small frequency response irregularities, the vertical delay of the indicator 10 can be started with a fixed delay relative to the synchronization pulses and (Fig. 2, s). For this purpose, a delay element must be provided in block 13. When measuring the frequency response of the absolute time delay, an exemplary quadrupole 7 in reference channel 2 is missing. Using the proposed device, the measurement error can be reduced by eliminating operations and means of intermediate signal conversion, as well as by the possibility of forming a scale on the screen of the raster indicator (scale scale simultaneously with the measured characteristic. In the described device, the limitation of the measurement range is excluded due to the measurement of the frequency The delay time of the device instead of the phase-frequency characteristic and by displaying the frequency characteristic of the delay time, the device allows you to simply (without additional calculation) control whether one of the conditions of the undistorted signal transmission is constant the phase time delay of communication channels, delay lines and other circuits. measuring the frequency characteristics of a quadrupole, containing a generator of varying frequency, connected to the inputs of an exemplary and under study Four-pole, raster indicator, characterized in that, in order to reduce measurement error and improve performance when measuring the frequency characteristics of the phase delay time, the output of the quadrupole under study is connected to the input of the raster indicator control unit through the second one the unit of selection of moments of reference is connected to the input of the unit of vertical scanning of the raster indicator, the unit of horizontal scanning of which th is connected to sync generator unit. Sources of information taken into account in the examination 1. Hewlett-Packard Journal, 1972, vol 2k, N 2, p. 12-20. 2. USSR author's certificate 37153, cl. G01 R 29/00, 1971 (prototype). e