SU1598183A1 - Method of measuring characteristic of group delay and amplitude-frequency characteristic of communication channel - Google Patents

Abstract

The invention relates to telecommunications and provides improved measurement accuracy. The transmission produces a periodic multi-frequency measurement signal (IC) with multiple frequencies, known amplitudes and phase shifts of the components. At the reception, zero transitions of the IC are isolated and its average period is measured, with a multiple of which the sampling frequency and measurement interval are chosen. At each period, the IC shifts the sampling rate phase, and the samples are stored in the form of the next column of the parametric matrix, the rows of which restore the IC and determine the amplitude and time shift of each frequency component of the IC, which allows determining the x-ku group delay time and amplitude frequency x-ku of communication channels. 2 Il.

Description

The invention relates to telecommunications and can be used to quickly measure the frequency characteristics of linear, group, and tone frequency channels.

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

Figure 1 shows the timing diagrams of the individual operations of the proposed method; Fig. 2 is a structural electrical circuit diagram of the device for implementing the proposed method.

A device for measuring the characteristics of a group deceleration time (GDT) and amplitude-frequency characteristic (AFC) of a communication channel includes a matching unit 1, a controlled shift register 2, a generator of 3 clock pulses, a generator of a multi-frequency periodic signal 4, a driver of 5 null transitions, analog -digital converter (ADC) 6, timer 7, block 8 priority

interrupts, microprocessor system (MPS) 9 and display 10.

The essence of the method is that a periodic multi-frequency measurement signal (Fig. 1 a) with multiple frequencies (frequencies are multiples of 100 Hz) is supplied to the input of the communication channel.

The period of a multi-frequency signal at the transmission is constant and equal to 0.01 s (which corresponds to a frequency of 100 Hz), which is a multiple of all measured frequencies in the communication channel band.

When passing through the communication channel, the amplitudes and phases of the harmonic components change, and the period of the signal changes (Fig. 16).

At the reception, null transitions of the multi-frequency signal are initially selected (Figure 1B). The duration of several periods is measured, averaged, and the average duration of the signal period T is determined.

the next

00

SA)

Then select the sampling frequency of the signal multiple of the average duration of the signal period. In this case, if for ensuring the given accuracy it is necessary to have on the signal period, for example (fig. 1d). points, the sampling rate of the signal

Fq

 one

one

vT 27T

In this case, it may be that the obtained frequency exceeds, for example (Fig. 1e), by the speed of computational operations. Therefore, 27 points cannot be received on one period of a multi-frequency signal.

If the sampling rate is a multiple of the signal period and quantization begins at the zero-transition point, then the required 27 points can be obtained in three periods of the multi-frequency signal. Therefore, at each of the three periods the sampling rate will be equal (Fig. 1e)

R

9-y7Also, at each subsequent period of the measured signal, the phase of the sampling frequency is shifted by an amount equal to its ratio to the number of quantized periods of the multi-frequency signal (Fig. 1e, g).

Level counts in the first period of the measured signal, labeled 10, 11,

1218 (figd), on the second-20, 21, 2228

(fig.1e), on the third - 30, 31, 3238

(fig, 1g), obtained at each shift, is remembered in the next column of the parametric matrix. The readings of the level of the measured signal (fig. 3), recorded for each period in its own column, in each of its lines, read from left to right and from top to bottom, make it possible to reconstruct a multi-frequency signal by points (fig. 1i). In this case, the recovered curve contains counts from all three periods.

Thus, the effect of the fg sampling frequency shift is equivalent to quantizing the measured signal with the Fg frequency.

Further determination of the characteristics of the GDT and the frequency response of the communication channel (Fig. 1k, l) is performed using Fourier transforms over the signal level counts, taking into account the sampling features of the proposed method.

The device for measuring the characteristics of the GDT and the frequency response works as follows.

A multi-frequency signal generator 4, controlled by microprocessor system 9, transmits to the communication channel a periodic

ten

five

0

50

50

multi-frequency measurement signal with

multiples of 100 Hz frequencies (300, 400

3400 Hz) and known amplitudes and phase shifts of the harmonic components.

At the reception from the communication channel, the multi-frequency signal, having passed the matching unit 1, is fed to the shaper 5 of the zero transitions and the ADC 6. The shaper 5 generates short pulses when the polarity of the signal from negative to positive is changed, i.e. twice on the signal period at the points of the zero transitions. The zero transition gates arrive at block 8 and at timer 7. At the other input of timer 7, clock cycles are received from the MPS generator 9. Timer 7 measures the intervals between two zero transitions (the duration of the multi-frequency measurement signal period). The data on the duration of the period are read in MPS 9, where they are averaged. The average sampling rate for the 3 clock pulse generator is determined by the average time, the period duration and the specified accuracy (the number of samples per period at a given reference accuracy). The frequency of the oscillator, 3 clock pulses, controls the MPS 9, and its phase is synchronized with the pulses of zero transitions. Depending on the speed of the MPS 9, it calculates the number of level measurement periods for the parametric matrix.

In the first measurement period, starting from the zero-transition of the beginning of the signal period, ADC 6 produces a sampling pulse from the controlled shift register 2 to read the levels of the multi-frequency signal, which, upon request from block 8, go to MMS 9. Here they are stored as the next element of the column parametric matrix. At the next zero-transition (after a given number of clock pulses), the frequency of the clock pulses is shifted by means of a controlled shift register 2.

Claims (1)

Then, in a similar way, the second and subsequent columns of the parametric matrix are formed. When all the columns of the matrix are recorded, the characteristics of the GDT and the frequency response in the MPS 9 are calculated. The results are shown in the form of graphs and tables for display on the display 10. The invention formula The method of measuring the characteristic of the group delay time and the amplitude-frequency characteristic of the communication channel consisting in the formation of a periodic multi-frequency measurement signal in the transmission in the band communication channel with multiple frequencies, known amplitudes and phase shifts of components, characterized in that, in order to improve measurement accuracy, zero-transitions of a multi-frequency measurement signal are selected at the reception, its average period is sampled, and the sampling frequency and interval are measured as multiples. measurement, the number of quantized periods of a multi-frequency measurement signal in which is equal to the ratio of the number of values of a multi-frequency measurement signal to be analyzed on its average period to the maximum possible To the number of values analyzed at the average period, the moments of the start of quantization of each period are combined with the corresponding null transitions of the multi-frequency measuring signal, the sampling frequency is reduced by a number equal to the number of quantized average periods, and at each subsequent period of the multi-frequency measuring signal, shift the phase of the sampling frequency by an amount equal to the ratio of its period to the number of quantized average periods of the multi-frequency measuring signal; the samples of the levels at each shift the phases are remembered as the next column of the parametric matrix, the rows of which restore the multifrequency the measurement signal, and the desired parameters for each component of the multi-frequency measurement signal are determined by the formulas Uk p yk ak + bk; Tk (arctg ak / bk + A) / 2, where n is the number of analyzed values of the multi-frequency measuring signal on one period; )BUT. 1sin -  l2k2 p ak  S Ay, + XM I 12  Ay, cosK L ± 2iM. Tk is the period of the kth frequency component of the multi-frequency measurement signal; Afik is the phase shift in the transmission between the kth and middle frequencies of the communication channel; K - harmonic number; x |, y |, Ay | -coordinates according to time, amplitude and its increment. Phie. one 4l