SU1762252A1 - Method for measuring of amplitudes of amplitude- modulated signals - Google Patents

Abstract

Usage: when measuring parameters of amplitude-modulated signals. SUMMARY OF THE INVENTION: The method consists in that the signal is sampled at each half-period of oscillation twice at times shifted by a quarter of the period relative to each other, the instantaneous values obtained are measured and used to calculate the amplitude values of each half-period. 3 il.

Description

This invention relates to electrical and radio measuring technology. In research practice, there is often a problem of measuring various parameters of amplitude modulated (AM) signals, which can be represented by the following model:

x (t) A (t) sin (a t + fp) (1) where A (t) is an oscillation envelope with frequency ω.

In this case, the information is contained in the envelope A (t), which is represented by the amplitude values of the oscillations at the frequency m. Thus, when analyzing the AM signals, the amplitude values of the oscillations are of considerable interest.

There is a method for measuring the amplitude values of the AM signals, including. that the signal is subjected to a 2-half-period rectification, differentiate and at each half-period the signal is integrated over a time interval limited by the moments of transition of the derived signal through specified values.

The disadvantage of this method is the narrow frequency range of signal analysis, limited to the low frequency range. The disadvantage of this method is also low accuracy, limited by interference of various origins.

The closest to the present invention is a method for measuring the amplitude values of AM signals, which means that the signal is sampled at a frequency significantly higher than its carrier frequency, the instantaneous values of the signal are encoded, the codes obtained for each half-period of carrier oscillations are compared with each other and the largest of them take for the amplitude value of the corresponding half-period of the carrier wave

The disadvantage of this method is the limited frequency range of the study of AM signals. This is due to the high rate of signal sampling and increased

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requirements for the speed of the analog-to-digital conversion (ADC) and computing device (WU), resulting in limiting the frequency range of the AM signals under study in the high frequency region.

For example, to provide an error in measuring the amplitude of a sinusoidal signal with a frequency of 20 kHz. caused only by discretization (dynamic error and quantization error are neglected) equal to 1%, the sampling rate in accordance with the expression

5 1 -cos (x 180) 100%

where d is the relative measurement error of the amplitude;

f is the signal frequency;

n is the number of conversions per second, must be at least 450 kHz.

The aim of the invention is to expand the frequency range of measurements of the amplitude values of AM-cni lines.

This goal is achieved by allocating the AM signal twice at each half-period of oscillations at time points shifted relative to each other by a quarter of the period, the instantaneous values of the AM-signal are measured and the amplitude value for each half-period of oscillations is calculated using the following formula .

xj.1p.

sin arctn (x, i / xj2) jv

XJH -:

where xjM is the amplitude value of the j-ro half cycle of oscillations,

X)) and xj2 are the instantaneous values of the j-ro half-cycle of co-bans.

Let us consider the proposed method in more detail.

Each half-period of the AM-signals can be represented by two readings shifted relative to each other by a quarter of the period (Fig. 1). These readings are represented by the expressions:

X) 1 XJM -Sirv7; tj XJM, (4)

x | 2 xjM Sin (r.tj +)

 XjM -Sin (“j + j) Xji icos“ j (5)

where Xji and Xj2 are the first and second counts of the j-ro half-period of the AM signal;

XJM is the amplitude value of the j-ro half-period;

tj is the moment of sampling the first reading of the j-ro half period relative to the beginning of the last.

To calculate the XJM from (4) or (5), it is necessary to determine the value. To do this, it is enough to divide (4) by (5):

xn xjM-sinaj

Xj, 7: COS "j (b

From where

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a - arctg--

1Xj2

Using (4) and (7), we get:

X (1 Xji

(7)

X | m sirTq sln arctg (Xji / xj2) J

Thus, by two readings, using (8), one can determine the amplitude value of the j-ro half-period.

The proposed method can be implemented using a device consisting of a sampling and storage device (VHF) 1, comparator 2, A / D converter 3, frequency multiplier 4, computing unit 5, input 6 and output 7. The input of device 6 is connected to the first input of the VH1 and the input of the comparator 2, the output of the WCH 1 is connected to the first input of the ADC 3, the second input of which is connected to the second input of the WCH 1 and the output of the frequency multiplier 4, the input of which is connected to the output of the comparator 2 and the first input of the block 5, the second input of which is connected to the first output of the ADC 3, the second output of which is connected to the third inputs UVH 1 and block 5, the output of block 5 is connected to the output of the device 7

The AM signal is fed to the input 6 of the device and then to the inputs of the WCX 1 and comparator 2. Comparator 2 compares the input signal with a zero potential and generates pulses at its output at the moments when the signal passes through 0. These pulses are fed to the first input of block 5, as well as to the input of multiplier 4, whose frequency multiplication factor is 2. Pulses with a double frequency following from the output of the multiplier

4 is fed to the second inputs of the VHF 1 and the A / D converter 3. In the course of this, the OIL 1 is transferred to the storage mode of the instantaneous values of the signal, and the A / D converter 3 starts up and encodes these values.

At the end of the coding process, a second pulse is generated at the second output of the ADC 3, which transfers the water economy device 1 to the signal tracking mode, and also records the code from the first output of the ADC 3 to block 5. Block

5, after recording the codes of two consecutive signal values into it, it is triggered by a pulse arriving at its first input, and calculates in accordance with (8) the amplitude value of the current half period of oscillations. The codes of the indicated values are in digital form at the output 7 of the device. The operation of the device is illustrated

also the timing diagram shown in FIG. 3

Claims (1)

From the above it can be seen that the proposed method provides a positive effect, which consists in expanding the frequency range of measurements. This expansion is provided due to a significant (with an error of 1% more than 5 times as compared with the prototype) a decrease in the signal sampling rate. The positive effect increases as the requirements for measurement accuracy increase, since in the prototype, the sampling frequency of the signal increases more and more in accordance with (2). and in the proposed method, it remains constant. Claims of Invention A method for measuring amplitude values of amplitude modulated signals. that is. that the signal is sampled, the instantaneous values obtained are measured, characterized in that, in order to expand the frequency range of the measurements, the sampling is performed twice on each half-period of oscillations at time points shifted relative to each other by a quarter of the period, and the amplitude value is calculated for each half cycle of oscillations by the formula one Xjm sin arctg (xji / xj2) 15 where XJM is the amplitude value of the j-ro half-period of oscillations; Xji and Xj2 are the instantaneous values of the j-ro half cycle. AT 5  Ml Fig.} Srg.2 hae FIG. 3