SU1746323A1 - Method of measurement of peak deviation of frequency - Google Patents

Abstract

The invention relates to a measurement technique and is intended to measure frequency deviation. The purpose of the invention is to improve the measurement accuracy due to the fact that after transferring the measured frequency modulated signal to an intermediate frequency equal to zero and changing the frequency of the local oscillator upward or downward until the peak deviation is equal to the deviation of the intermediate frequency from zero, the specified equality is determined by the equality of the intermediate frequency to the average frequency of the converted frequency modulated signal. 2 Il.

Description

J

The invention relates to a measuring technique and can be used, in particular, in measuring complexes of parameters of frequency-modulated (FM) signals.

The purpose of the invention is to improve the measurement accuracy.

FIG. 1 shows graphs explaining how to perform operations of the method; in fig. 2 is a block diagram of a device for implementing the proposed method.

When implementing the method of the original FM signal

u (t) is Asln (2 f0t + 2 (t) dt), where A is the amplitude of the FM signal;

fo is the carrier frequency;

Ф (t) - deviation of the instantaneous frequency from the carrier, is transferred to the intermediate frequency

tVw fo fr, where fr is the local oscillator frequency,

wherein fri4 is set to zero.

Peak frequency deviations, FM signal equal: frequency deviations Down

(F (1)) AfH, frequency deviation Up

max (F (t)) AfB

The average frequency of the converted FM signal by definition

1 T

fcp - / kpch + fyuotoch, and about

2

a so yo oo

where Ti is the measurement time;

frw + Ф $ - instantaneous frequency of the converted FM signal.

With fr ™ Afn, the average frequency is greater than the intermediate frequency, since

Ter

-fT / neither

1and o

+ F (g) I dt

 fn4-2T (t) ..

T th til

where (t2i - tn) is the time interval when frw + + Ф (t) 0.

As the frequency of the local oscillator increases or decreases from fr fo, the difference between the average frequency fcp and the intermediate frequency frm decreases, becoming zero at fcp fnn A f and remaining equal to zero with a further increase in frm. which is proved as follows.

With I ™ / AfH (or fn4 / AfB), the average frequency of the converted FM signal is always equal to the intermediate frequency frm fcp, since fnn + F (t) / 0 for all t. Besides

Fyu

dt 0.

The latter is carried out with Ti, a multiple of the period of the modulating signal Tm, or with Ti and Tm.

In this way

fcp fn4 if tpc / afe or f ™ / Afn;

fcp fn4 if fi ™ AfB or fnn A fH.

As a result, if at increasing (from the value equal to zero) the intermediate frequency, we notice the value of frm at which the values of fcp and frm compare, then regardless of the form of the modulating signal frw Afs with increasing frequency of the local oscillator or fnq Afn with decreasing frequency heterodyne.

8 as an illustration (Fig. 1), the dependences of fcp and tpch on fr are given. The fCp dependence on f is based on the expression

2Af

P

frm args: p fn4, i fmu; r-f USG51P-g-f 1 -

Afaf / af

fair with sinusoidal modulation law.

In another form of the modulation law, the form of the fcp as a function of fr varies in the region (fo - A fH / fr / (fo + A fB)) as before merging with the dependence of frw on fr in the regions fr fo - AfH, fr fo + A fB.

Since in the proposed method the moment of equality of the peak frequency deviation to the variation of the intermediate frequency is fixed by the equality of the average and intermediate frequencies, Ј the measurement accuracy of these frequencies does not depend on the modulation index, therefore, the accuracy of the proposed method does not depend on the modulation index of the measuring FM signal .

The use for fixing the said equality of information about the magnitude of the frequencies makes it possible to easily use the proposed method in information-measuring systems, since the frequency meters, for example, of type 43-64 have an output

information to the public channel (CPC)

Thus, an introduction to the method of measuring the frequency deviation based on transferring the measured frequency-modulated signal to an intermediate frequency equal to zero, changing the frequency of the local oscillator upwards or downwards until the peak deviation equals the deviation of the intermediate frequency from zero, measuring the intermediate and middle frequencies of the converted frequency modulated signal, and achieving equality is determined by the equality of the intermediate

0 frequency is the average frequency of the converted frequency modulated signal, which allows to increase the measurement accuracy, since the measurement accuracy of the average frequency of the converted FM signal and intermediate

5 frequencies using the ESCh does not depend on the magnitude of the modulation index, and also allows the use of the method as part of automated information-measuring systems.

0 The device (FIG. 2) contains a frequency converter 1, a local oscillator 2, a meter 3 of the average frequency of the converted FM signal, a meter 4 frequency of the local oscillator, a meter 5 of the carrier frequency of the FM signal.

5 Any high-frequency industrial generator, for example, G4-165, can be taken as the local oscillator, and the frequency meter of the converted FM signal, the carrier frequency of the FM signal and the frequency of the local oscillator can be any frequency meter, for example, an electron-counting frequency meter 43-64.

The intermediate frequency can be measured in various ways: 5 for example, the carrier frequency fo of the measured FM signal and the local oscillator frequency fr are measured, and the intermediate frequency is determined by the formula frm (fo - fr).

The meter 5 measures the carrier frequency of the FM signal, and the meter 4 measures the frequency of the local oscillator, then sets the frequency of the local oscillator 2 equal to the carrier frequency of the FM signal and thus the transfer is carried out by the converter 1

5 of the frequency of the carrier frequency of the FM signal to an intermediate frequency equal to zero; Then the frequency of the local oscillator 2 is tuned upwards when measuring the frequency deviation Up or downwards when measuring the frequency deviation

Down until the intermediate frequency equals the center frequency of the converted frequency modulated signal. At this moment, the peak frequency deviation is equal to the center frequency and the intermediate frequency of the converted frequency modulated signal.

Claims (1)

A method for measuring peak frequency deviation based on transferring a measured frequency modulated signal to W I Editor N. Bobkova Compiled by V. Novoselov Tehred M.MorgentalKorrektor L. Beskid intermediate frequency equal to zero, changing the frequency of the local oscillator in the direction of increasing or decreasing to achieve equality of the peak deviation the deviation of the intermediate frequency from zero, characterized in that, in order to improve the accuracy of the measurement, the achievement of equality is determined by the equality of the intermediate frequency of the average frequency of the converted frequency modulated signal. fo + Јfe FIG. g