SU1053020A1 - Method of measuring frequency deviation - Google Patents

Abstract

METHOD OF MEASURING FREQUENCY DEVIATION by transferring the signal to a zero intermediate frequency of changing and fixing the phase of the heterodyne signal until the converted signal coincides with the zero level while removing the modulation and re-modulating the input signal in order to simplify the method when expanding its functionality and the range of measured modulation indices, after re-modulating the input signal, the phase of the heterodyne signal is changed and fixed to coincide with the extreme value reobrazovannogo signal with zero level, and the frequency deviation measured by the LO signal phase difference and the number of intersections of the converted frequency-modulated signal and the maximum, minimum and zero levels for a quarter of the modulation period excluding the first. (L ate co to

Description

The invention relates to a pulse technique. An oscillographic method for measuring the frequency deviation is known, which consists in measuring the extreme instantaneous frequencies and the average frequency of the frequency-modulated oscillation. A disadvantage of this method is that it is suitable only for measuring a signal with a large modulation index. The closest technical solution to the present invention is a method for measuring the frequency deviation, which consists in setting the intermediate frequency of the converted frequency-modulated signal equal to zero, changing the phase of the heterodyne signal until the transformed signal coincides with the zero level when the signal is removed. of the input signal, note that the amplitude value of the transformed signal in the presence of modulation, change the intermediate frequency of the transformed signal, change the amplitude of the transformed signal. and removal of the signal modulation to match it with the init flax marked level determined amplitude ratio N .dvuh converted si1- catch: the first at zero intermediate frequency and a modulated input signal and the second at an intermediate frequency is not equal to zero. and the unmodulated input signal, calculate the frequency deviation 2 by the formula .. 3 FP .Fo (rcsih N, where / 3 is the modulation index; F is the frequency of the modulated signal. However, the method requires complicated instrumentation and is applicable only to harmonic modulating signals and the index is limited to A., since for any 7g p, the - amplitude of the transformed frequency-modulated (FM) signal is equal to the amplitude of the transformed unmodulated signal at an intermediate frequency not equal to zero, and the ratio of amplitudes N 1 and , sit from great Frequency deviations. The purpose of the invention is to simplify the method while expanding its functional capabilities and the range of measured modulation indexes. The goal is achieved by the fact that the method of measuring frequency deviation by transferring the signal to a zero intermediate frequency and changing the heterodyne phase cHrHaha before the converting signal with the zero level coincides with the removed modulation and the re-modulation of the input signal after the re-modulation of the input signal, the phase of the heterodyne signal is changed and fixed The coincidence of the extremal value of the transformed with the zero level, and the frequency deviation are determined by the phase difference of the heterodyne signal and the number of intersections by the converted frequency. Modulated signal of the maximum, minimum and zero levels during a quarter of the modulation period, excluding the first one. Figure 1 shows signal plots explaining the steps of the method; Fig. 2 is a block diagram of a device for implementing the proposed method. . A device for implementing the proposed method contains a series-connected phase detector 1, a low-pass filter 2 (LPF), a local oscillator 3, a phase shifter 4 connected in parallel with it, a phase meter 5, a phase shifter 6, a frequency converter 7, a low-pass filter 8 and an oscilloscope 9., The method is implemented as follows. The frequency of the local oscillator 3 is set equal to the average frequency of the input frequency-modulated (FM) signal, i.e. The average intermediate frequency at the output of frequency converter 7 is zero. In this case, the low-pass filter 2, whose cut-off frequency is lower than the frequency of the modulating signal, eliminates from the voltage controlling the frequency of the local oscillator 3 frequency components that determine the law of the FM, which eliminates the demodulation of the converted FM si-nal. After removing the modulation from the input signal, the signal applied to the baseband. Cytograph 9 is a constant voltage whose level is equal to e (t) U, yf (4o) where OORI is the amplitude of the converted FM signal; Vfl - the initial phase shift. After presetting the phase shifter 4 to the zero position, with the phase shifter 6, the phase shift signal is changed to match the transformed signal with a zero level, i.e. The line observed on the oscilloscope screen 9 is set to the oscilloscope sight line 9. / At the same time, e (t) Uon4f (o where V is the phase shift introduced by the phase shifter 6. When modulation is turned on, the signal on the oscilloscope screen 9 in the case of ft looks like, shown in fig.la.

The phase of the heterodyne signal is changed by the phase shifter 4 to match the extreme value (for example, the maximum) of the transformed signal with a zero level, i.e. with the line of sight of the oscilloscope 9 (figure 1). In this case, the phase meter 5 measures the phase shift of the heterodyne signal introduced by the phase shifter 4, f f which in this case is direct, o is equal. modulation index / j, since

, o, xte (t) J Won4 (p + VV / S. - iJonM H-o- V,)

those. ..

JT - If -2- ft4Ji, signal signal

the input of the oscilloscope 9 has the form shown in Fig. 18. In this case, the phase of the heterodyne signal is changed in such a way that the extreme value, for example, T. A, of the converted signal first approaches the amplitude value of this signal, i.e. to the BV line, and then to the zero level, i.e. to the line of sight of the oscillograph 9 DG (Fig. 1d). If, however, the phase of the heterodyne signal is changed in such a way that mA moves by the shortest path to the line of the DG (Fig. 13), then in the case of a phase reading (5f meter connected with the modulation index by the ratio.

p, - | if | + jr

In the general case, for any value of x / 5 (Fig. 1e), moving the oscilloscope with the shortest path, r & l to the sight line, is obtained by means of an oscilloscope connected with the engine. dex modulation formula.

, ) l- (1,) l.

where / is the readings of the phase meter 5;

CH L ETHNOE)

xll (to - in short). k is the number of intersections by the converted FM signal of the maximum, minimum, and zero levels for a quarter of the modulation period, excluding the first (zero) point.

As an example, a converted FM signal is shown in FIG.

at 2Ti, with the number of points

intersections is four.

Determine the frequency deviation

20, formula

   ) (/ J. (1..xA) |.

25 Thus, due to the fact that the phase of the heterodyne signal is measured in two cases; the first, with the unmodulated input signal and the converted signal level equal to zero, and the second, with the modulated input signal and the extreme value of the converted signal coinciding with the zero level, the measurement method is simplified, the range of measured modulation indexes is expanded, and the functional the possibilities of the method, since the requirements for the input signal shape and the magnitude of the nonlinear distortions introduced by the transducer are reduced

40 frequencies.

Claims (1)

METHOD FOR MEASURING FREQUENCY DEVIATION by transferring a signal · to a zero intermediate frequency of changing and fixing the phase of the heterodyne signal, until the converted signal matches the zero level when the modulation is removed and the modulation of the input signal is repeated; that, in order to simplify the method while expanding its functionality and the range of measured modulation indices, after repeated modulation of the input signal, the phase of the heterodyne signal is changed and fixed until the extreme value of the converted signal coincides with a zero level, and the frequency deviation is determined by the phase difference of the heterodyne signal and the number the intersections of the converted frequency-modulated signal of the maximum, minimum and zero levels for a quarter of the modulation period, excluding the first. I