Device for measuring the amplitude-frequency characteristics of the communication path

 

(57) Abstract:

Usage: in telecommunications to perform automated measurements of frequency response and group of linear channels of transmission systems on cable, radio and other communication lines. The inventive device comprises a block 1 of the registration and control data generator 2, the resistors 3.1 - 3.4 isolation amplifiers 4.1 - 4.4, measured tract 5 communications, detectors 6, block 7 subtraction, the transmitter 8 and the receiver 16. The device allows a single measurement of the frequency response of the communication path for each of the selected control frequency, which greatly improves performance measurements frequency response. 2 C.p. f-crystals, 5 Il.

The invention relates to telecommunication and can be used to perform automated measurements of amplitude-frequency characteristics (AFC) of the group and of linear channels of transmission systems on cable, radio and other communication lines.

A device for measuring the amplitude-frequency characteristics of the communication channel containing the measuring generator, a control unit, a measuring unit, a threshold unit, forward and reverse channels.

A disadvantage of the known device is a long time smerek the invention is a device, implementing a method of measuring the amplitude-frequency characteristics of the communication path that contains the control unit and data logging measurements, generator, resistors junction, the measured communication path, the detector, the comparator, the transmitter as the signal return path communication receiver as signal amplifiers.

The disadvantage of this device is the low performance measurements frequency response of the communication path, as each controlled frequency steps increases the level of the measuring signal as long as no work the comparator at the receiving station, and then check the measurement data and shall include the following frequency of the measuring signal.

The purpose of the invention improve performance measurement of the amplitude-frequency characteristics of the communication path by transmission on each frequency of the measuring signal to transfer measurement in a communication channel as the ratio of the amplitudes of the two harmonics of nonlinear distorted vibrations.

The aim is achieved in that in a device for measuring the amplitude-frequency characteristics of the communication path containing the serially connected control unit and record measured data, the gene of the junction and the detector, connected in series transmitter, the third resistor junction, a third amplifier, a reverse communication path, the fourth amplifier, a fourth resistor junction and the receiver, the output of which is connected to the input of the control unit and data logging of measurements entered the subtraction unit, the first input of which is connected to the detector output, the second input of the subtraction is input to the reference voltage, and the output of the subtraction unit is connected to the transmitter input.

In Fig.1 shows a block electrical diagram of the device for measuring the amplitude-frequency characteristics of the communication path. The device comprises a block 1 control register data measurements, the generator 2, the resistors 3.1. 3.4 isolation amplifiers 4.1.4.4 measured tract 5 connection, the detector 6, block 7 subtraction, the transmitter 8, consisting of the amplifier-modulator 9, the additional generator 10, two bandpass filters 11.1 and 11.2, the frequency Converter 12, the sinusoidal voltage generator 13, an amplifier 14, a reverse path 15 communication and the receiver 16, which consists of two bandpass filters 11.3 and 11.4, two additional detectors 17.1 and 17.2 and divider 18 voltage.

In Fig.2 shows a variant of the structural electrical circuits of block 1 governance and region is 20 clock pulses, the counter 21, the d / a Converter 22, 23, an analog-to-digital Converter, a multiplexer 24, the element 25 of the delay memory cell 26, the indicator 27.

In Fig.3 shows graphs illustrating the operation of the amplifier modulator 9, where (a) the transfer current-voltage characteristic of the element (bipolar transistor); b) the timing diagram of the input sinusoidal voltage; a timing chart of the output current of the amplifier.

In Fig.4 shows graphs of the coefficients Bergk(expansion coefficients of the cosine pulse output current of the amplifier-modulator 9) from the cutoff angle of the output currentwhere the coefficient Berg is the ratio of the amplitude of the IMCspectral component (harmonic) current to the pulse amplitude Imaxcurrent: ato= Imk/Imax.

Device for measuring the amplitude-frequency characteristics is as follows.

When the button 19 start a generator of clock pulses 20 and the count of these pulses by the counter 21, the output of which is fed code combination on the d / a Converter 22, the output of digital to analog conversion max is 2, the signal passes through resistor 3.1 decoupling amplifier 4.1 and later in the measuring path 5 links, output path 5 connection of the measuring signal passes through the amplifier 4.2 and the resistor junction 3.2 and falls to the input of the detector 6, the output of which goes to the input unit 7, subtraction, where the comparison of the level of the measuring signal with the threshold voltage Up. From the output of the unit 7 subtracting the resulting voltage is fed to the input of the transmitter 8, where the differential voltage is fed to the control input of the amplifier-modulator 9, the second input is connected to the output of the additional generator 10 that generates a harmonic signal. The values of the frequencies of the harmonics of the output signal of the amplifier-modulator 9, containing a nonlinear element, which does not depend on the amplitude of the voltage at its control input, as determined by the frequency of harmonic oscillations from the output of the additional generator 10. As the bias voltage Ecm=Ub(t)=Eb+U2(t) is the output voltage of the block 7 subtraction. The bias voltage at the control input of the amplifier-modulator 9 is not necessarily positive. It is determined by the amplitude of the harmonic oscillations from the output of the generator 10 and the desired range of variation of the cutoff angle. In this case, the block 7 subtraction performs other funny output voltage from block 7, which is determined by the level of the frequency response of the communication path. The circuit elements of the amplifier-modulator 9 are selected so that the bias voltage supplied to its control input, would provide a nonlinear mode of operation of this amplifier 9. In this case, the input of the amplifier is a high-frequency signal, a current which has a cutoff angle and a certain amplitude of the harmonics Im1, Im2This signal is applied to the inputs of bandpass filters 11.1 and 11.2, the first of which is configured on the frequency of the first harmonic component of F1and the second filter 11.2 on the frequency of the second harmonic component of F2=2F1the output signal of the modulator 9. From the output of the second bandpass filter 11.2 frequency of the second harmonic component of Im2is fed to the input of the frequency Converter 12, to the control input of which receives the auxiliary sinusoidal voltage from the generator 13. The converted signal close in frequency to the frequency of the first harmonic component of the output signal of the amplifier-modulator 9, the output of the frequency Converter is supplied to the amplifier 14. From the output of the transmitter 8 signals at frequencies F1and FPpass through the resistor 3.3 rasur interchange 3.4. The signal is then fed to the input of the receiver 16 and falls to the inputs of bandpass filters 11.3 and 11.4. The first band-pass filter 11.3 tuned to the frequency of the first harmonic and the second band-pass filter 11.4 on the frequency of the second harmonic. With outputs of filters 11.3 and 11.4 filtered harmonic components are received at the inputs respectively of the first and second additional detectors 17.1 and 17.2, designed to determine the amplitudes of the first and second harmonic components of the signal. The outputs of the additional detectors 17.1 and 17.2 are connected and the corresponding inputs of the divider 18 voltage intended for finding the ratio between the amplitudes of the first and second harmonics. In Fig.5 shows graphs explaining the operation of the individual blocks of the device and reveal the correspondence between the attenuation tract 5 (upper graph shows the amplitude-frequency response K(F) measured tract 5) and a value of the signal at the output of the voltage divider 18 (lower graph). The number in the circle indicates the number of the block in which physical process is illustrated by the corresponding plot of the voltage. The frequency generator 2 during the time interval measurement of the frequency response t [t1,t2] changes from what ignal output path 5 will also be modified in accordance with the frequency response in the passband tract 5. The envelope of this signal is allocated by the detector 6, and after passing through the block 7 of the subtraction is supplied as a bias voltage to the input of the amplifier-modulator 9, the second input of which receives the harmonic oscillation output from the generator 10. The amplifier-modulator operates in a mode with current cutoff, the value of the cutoff angle is determined by the bias voltage, and therefore, the frequency response of the path 5. The amplitudes of the first and second harmonic components of the modulated signal at the inputs of the respective bandpass filters 11.3 and 11.4 are also determined by the value of the cutoff angle. Therefore, the output signal of the divider 18, the entrance of which serves the above-mentioned harmonic components is also determined by the value of the cutoff angle, and therefore, are positively correlated with the frequency response of tract 5 connection. In practice we often face the task of measuring the frequency Response of the direct path, and the frequency response of the reverse path is known. As follows from Fig.3, with a uniform frequency response of the controlled path of connection and therefore at a stable angle cutoff of the output current of the amplifier-modulator 9 the ratio of the amplitudes of the harmonics will be constant regardless of the magnitude of the damping of oscillations in the reverse path 15 connected. In the case of uneven frequency response value uprazheniya signal at the input of the divider 18 voltage, coming to the entrance of block 1 control. Input unit 1, the control enters the analog-to-digital Converter 23, where in digital form is fed to the information inputs of the multiplexer 24. On the control inputs of multiplexer 24 filed code combination from the output of the counter 21 through the element 25 delay on the frequency at which the currently measured level of response. Depending on the signal at the control input of the multiplexer 24, the measurement result of the frequency response is written in the corresponding cell of the memory 26. The time of measuring the frequency response of the communication path at the same frequency is not determined by the duty cycle and period of the pulses from generator 20 clock pulses. The increase in the content of the counter 21 is set at "1" increases the voltage level at the DAC output, which served as the control input of oscillator 2 and rebuilds it to a specific frequency. As the DAC can be used chip type TO PA, KPA, KPA and other Outputs of the memory cells 26.1. 26. N is connected to the input of the indicator 27 for the purpose of visual status display of the frequency response of the communication path in the measured frequency range.

Thus, the proposed device allows a single izmereniya frequency response compared to the prototype. If the measurement results do not depend on the level of attenuation in the reverse path communication.

1. Device for measuring the amplitude-frequency characteristics of the communication path containing the serially connected control units and data logging, the generator, the first resistor junction, the first amplifier, the output of which is input the measured communication path, the second amplifier, the input of which is the input of the output signal measured communication path, the second resistor junction and the detector, connected in series transmitter, the third resistor junction, a third amplifier whose output is the input of the reverse communication path, the fourth amplifier, the input of which is the input signal from the output of the reverse communication path, the fourth resistor junction and the receiver, the output of which is connected to the input of the control unit and recording data, characterized in that the input unit subtracting the first input of which is connected to the detector output, the second input of the subtraction is input to the reference voltage, and the output of the subtraction unit is connected to the transmitter input.

2. The device under item 1, characterized in that the transmitter is designed in the form of series-connected generator and amplifier-mod is uceni to the output of the amplifier-modulator, the output of the second bandpass filter connected to the first input of the frequency Converter, a second input connected to the output of the generator, and the output connected to the input of the amplifier, the output of which is combined with the output of the first bandpass filter and an output of the transmitter.

3. The device under item 1, characterized in that the receiver is made in the form of serially connected to the first bandpass filter, a first detector and a voltage divider whose output is the output of the receiver, connected in series to the second bandpass filter, whose input is combined with the input of the first bandpass filter and an input of the receiver, and the second detector, the output of which is connected to the second input of the voltage divider.

 

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