CN107576879B - Frequency sweep measuring device and method for estimating cable attribute - Google Patents
Frequency sweep measuring device and method for estimating cable attribute Download PDFInfo
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- CN107576879B CN107576879B CN201710624778.3A CN201710624778A CN107576879B CN 107576879 B CN107576879 B CN 107576879B CN 201710624778 A CN201710624778 A CN 201710624778A CN 107576879 B CN107576879 B CN 107576879B
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Abstract
The invention discloses a sweep frequency measuring device and a method for estimating cable attribute, which are characterized in that a bi-directional coupler module is arranged and is configured to perform directional coupling sampling output on a transmitting signal and a reflecting signal respectively, the coupled sampling signal is input into a corresponding power measuring module, the power measuring module is configured to measure and collect signal power output by different output ports of the bi-directional coupler module, only amplitude information of the reflecting signal can be measured, the complexity of the measuring device is reduced, the anti-interference capability of the measuring device is improved, the cable length can be estimated relatively accurately through analysis of frequency domain data, whether the characteristic impedance of a cable changes is judged, and whether the cable is damaged or not is judged.
Description
Technical Field
The invention relates to a frequency sweep measuring device and a method for estimating cable properties.
Background
The communication cable is used for near-distance audio communication, long-distance high-frequency carrier digital communication and signal transmission, and is widely applied to important fields of communication line transmission, instruments, electric power and the like. The cable mainly comprises a local telephone communication cable, a high-frequency coaxial communication cable and the like; faults such as short circuits, open circuits, etc., may occur in the communication cable due to various external factors. It is therefore necessary to estimate the cable properties by a simple device and a simple and effective method, mainly including estimating the length of the cable, whether the characteristic impedance of the cable is abnormal or not.
In order to estimate the attribute information of the communication cable and reduce the workload of manual troubleshooting of cable faults, the invention provides a simplified frequency sweep measuring device and a method for estimating the cable attribute by analyzing the frequency domain characteristic of the cable reflection coefficient measured by the device, so that the estimation of the length of the communication cable and the judgment of whether the characteristic impedance of the communication cable is abnormal or not are realized.
In a common frequency sweep measurement system, such as a network analyzer, a portable radio frequency analyzer, etc., the function is very powerful, and not only can amplitude information (reflection coefficient, return loss, voltage standing wave ratio) of a load to be measured in a frequency sweep manner, but also phase information (phase difference between an incident signal and a reflected signal) of a reflected signal can be measured. Although the measuring system has high precision and wide supported frequency range, the device has larger and complex equipment and high cost, is mainly used for measuring and evaluating high-precision devices such as precision radio frequency cables, antennas and the like, and is not suitable for low-cost popularization and use.
The patent of 'device and method for monitoring and positioning damage of cable shielding layer based on radio frequency reflected power' with application number 2016110399356 provides a device and method for monitoring the state of cable shielding layer on line in real time only by measuring reflected power, but the cable state analysis method is too complicated and requires a platform and a database to be supported by a complex algorithm to realize cable length measurement and fault analysis, and background software development difficulty is large; the attribute information of the cable cannot be obtained through a small number of frequency sweep measurements.
Patent No. 102879703a, "a grounding performance monitoring system and a method for dynamically monitoring the shielding layer of a communication cable" provides a method for dynamically monitoring the integrity of the shielding layer of a wired communication cable by measuring the capacitance of the shielding layer to the core. However, because the capacitance signal is too single, the quantity of the state information of the carrying cable is limited, and the cable in a complex environment is difficult to perform positioning analysis. Meanwhile, the internal resistance of the signal source is not matched with the input impedance of the transmission line, so that the measurement precision is low and the error is large. In addition, the method cannot accurately estimate attribute information such as cable length, cable characteristic impedance change and the like.
Disclosure of Invention
The invention provides a sweep frequency measuring device and a method for estimating cable attribute, which only measure the amplitude information of a reflection signal, reduce the complexity of the measuring device and improve the anti-interference capability of the measuring device, relatively accurately estimate the length of a cable by analyzing frequency domain data, judge whether the characteristic impedance of the cable changes and further judge whether the cable is damaged.
In order to achieve the purpose, the invention adopts the following technical scheme:
a swept frequency measurement device, comprising:
the sinusoidal wave signal generating module is configured to generate a frequency-adjustable sinusoidal signal as a transmitting signal source through a DDS technology;
the adjustable power amplification module is configured to adjust the transmitting power of the sine wave frequency sweeping signal generation module according to the actual condition requirement;
the connector impedance matching module is configured to form a circuit network with adjustable output side impedance by using transformers with different transformation ratios and matching resistors, so that the circuit network can perform impedance matching on cables with different impedance types;
the double directional coupler module is configured to perform directional coupling sampling output on the transmitting signal and the reflected signal respectively and input the coupled sampling signals to the corresponding power measurement modules;
the power measurement module is configured to measure and collect signal powers output by different output ports of the dual directional coupler module;
and the MCU control module is configured to be connected with the sine wave signal generating module, the adjustable power amplifying module, the power measuring module and the joint impedance matching module, and is used for scheduling and coordinately controlling the modules so as to monitor the state of the shielding layer of the communication cable.
The dual directional coupler module comprises an input port, a pass-through port, a first coupling port, a second coupling port and an isolation port; the directional coupler is used for sampling a sweep frequency reflection signal, the sweep frequency emission signal is input from the input port of the directional coupler, the first coupling port and the second coupling port are used for outputting sampling signals of the directional coupler for the sweep frequency emission signal and the reflection signal, the through port is used for outputting the sweep frequency emission signal or the input reflection signal passing through the directional coupler, and the isolation port is suspended.
The MCU control module is also connected with a display module and an LCD display screen for displaying charts, and the sweep frequency measurement result can be displayed.
Furthermore, the first coupling port and the second coupling port of the dual directional coupler module are connected with the MCU control module and the power measurement module through the RF switch module, and switching is realized through the RF switch module.
Preferably, the RF switch module is a single-pole double-throw switch, allowing high-frequency analog signals to pass through.
Furthermore, the power measurement modules comprise two modules which are respectively connected with the first coupling port and the second coupling port.
The load cable is a communication cable to be measured and is connected with the measuring device.
The sweep frequency measurement method based on the device comprises the following steps:
(1) connecting the load cable with the connector impedance matching module, and adjusting the connector impedance matching module to match the output of the detection device with the input impedance of the load cable;
(2) the MCU control module controls the sine wave signal generating module to generate a sine signal with a certain fixed frequency and inputs the sine signal to the adjustable power amplifying module;
(3) the MCU control module controls the adjustable power amplification module to adjust the sine signal to set power and inputs the sine signal to the bi-directional coupler module, the bi-directional coupler module performs coupling sampling on a transmitting signal, the RF switch module is switched to be connected to a first coupling port of the bi-directional coupler module, and a sampling signal is input to the power measurement module; transmitting signal main energy to be coupled into a load cable through a bi-directional coupler module and a joint impedance matching module;
(4) the MCU control module controls the power measurement module to measure the input signal power, and after the measurement result is stable, the transmission signal power data measured by the power measurement module is recorded and stored; after the completion, the MCU control module controls the RF switch module to be switched to a second coupling port of the dual directional coupler module;
(5) after the sinusoidal signal is coupled into the load cable, reflections can be generated at the end of the communication cable or at spatial locations where impedance discontinuities occur; the reflected signal is transmitted along the original path in a reverse direction and passes through the connector impedance matching module;
(6) the reflected signal is continuously transmitted to a dual directional coupler module, the module samples and couples and outputs the reflected signal, and then the reflected signal is coupled to a power measurement module through an RF switch module;
(7) the MCU control module controls the power measurement module to measure the input signal power, and after the measurement result is stable, the reflected signal power data measured by the power measurement module is recorded and stored;
(8) the MCU module controls the sine wave signal generation module to generate a sine signal of the next frequency point, and the steps (3) to (7) are repeated; after measuring all data of the preset frequency points, executing (9);
(9) the MCU module calculates and counts the frequency sweep measurement result, calculates the return loss, the reflection coefficient and the voltage standing wave ratio of the tested load cable at each frequency point, and displays the return loss, the reflection coefficient and the voltage standing wave ratio in a display module in a chart form;
in the step (1), the impedance matching module outputs differential pins, and the connection modes are different according to different types of cables and different cable attributes; for the attribute measurement of a certain twisted pair in a communication cable, a differential pin is directly connected with the twisted pair; for the condition of measuring the property of the shielding layer of the communication cable, one of the differential pins needs to be connected with the shielding layer of the cable, and the other differential pin needs to be connected with any core wire; for coaxial communication cables, the differential pins are connected to the shield and the central axis, respectively.
In the step (5), after the signal is coupled into the load cable, where the impedance between the cable shielding layer and the core wire is changed, the impedance mismatch generates a reflection, and the reflected signal is transmitted to the connector impedance matching module along the load cable, then transmitted to the dual directional coupler module, and finally transmitted to the power measurement module through the RF switch module for power measurement.
In the step (8), the measuring device sets different sweep frequency ranges and sweep frequency intervals for different types of communication cables in different environments, and stores the setting information to the MCU control module for automatic sweep frequency measurement.
In the step (9), three common reflection parameters, namely a corresponding reflection coefficient, a voltage standing wave ratio and a return loss, can be calculated through the measured powers of the transmitted signal and the reflected signal, so that the calculation and statistics of the frequency sweep measurement result are realized.
Specifically, the method for estimating the cable property through the sweep frequency reflection coefficient comprises the following steps:
(I) firstly, carrying out sweep frequency measurement on a communication cable with a known length to obtain a return loss frequency spectrum of the cable, recording the number of complete waves in the return loss frequency spectrum corresponding to the cable with the known length, and calculating the number of curves in the return loss frequency spectrum corresponding to the cable with the unit length to fluctuate, and recording the number as N0;
(II) carrying out frequency sweep measurement on other cables with unknown lengths, similarly obtaining a frequency spectrum of return loss, counting the number of curves in the frequency spectrum which fluctuate, marking the number as N, and calculating the length estimation value L of the cable to be N/N0;
(III) carrying out frequency sweep measurement on the deployed intact communication cable, and recording standard measurement data as a comparison reference for judging whether the impedance characteristic of the cable is abnormal or not;
(IV) periodically carrying out frequency sweep measurement on the communication cable in operation, and if the difference between the measured return loss spectrum and the reference spectrum exceeds a set value, indicating that the impedance characteristic of the communication cable is changed and the cable is possibly damaged or abnormal.
In the step (I), the sweep reflection parameters include three parameters of reflection coefficient, voltage standing wave ratio and return loss.
In the step (I), from the perspective of signal measurement, the change rule of the return loss spectrum is the reflection of the phase information of the sweep frequency signal in the amplitude value information due to the superposition of the wave, which is equivalent to indirectly measuring the phase information of the sweep frequency signal.
The return loss frequency spectrum shows fluctuation change, and the phase of a transmitting signal is gradually delayed due to the existence of cable distributed inductance and capacitance in the transmission process of the transmitting signal in a communication cable; because the space structure of the cable is relatively fixed, and the distributed inductance and the distributed capacitance can also be regarded as inherent properties of the cable, the speed of signal phase delay is also fixed for the same cable structure;
when the reflection occurs when the transmission is transmitted to the tail end of the cable, a reflection signal with the same frequency and different phase with the transmission signal is formed; the reflected signal and the transmitted signal are subjected to wave superposition in the transmission process, partial standing waves are formed due to different phases, energy flux density of the transmitted and reflected electromagnetic waves is uneven, energy coupling efficiency is reduced, and the frequency spectrum of return loss is fluctuated and changed along with the difference of the phase difference between the transmitted signal and the reflected signal.
Compared with the prior art, the invention has the beneficial effects that:
(1) through the implementation of the invention, the cable properties including the cable length and the change of the impedance characteristic of the cable can be measured and estimated through a simpler and cheaper device;
(2) by implementing the method, the measurement and estimation of the cable attribute can be completed by engineering personnel in a short time, and the state analysis and the maintenance of the cable are facilitated;
(3) the invention only collects the amplitude value data of the reflected signal, has stronger adaptability to complex electromagnetic environment, simple device and low cost; the robustness in function and structure is stronger, and the practicability is higher.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, are included to provide a further understanding of the application, and are incorporated in and constitute a part of this application for purposes of illustration and description.
FIG. 1 is a diagram of the hardware components of the apparatus of the present invention;
FIG. 2 is another alternative measurement configuration;
FIG. 3 shows the measurement results of a 35m coaxial line A (thinner);
FIG. 4 shows the results of measurements on a 35m coaxial line B (thicker);
FIG. 5 shows the measurement results of 200m (A) coaxial cable;
fig. 6 shows the measurement results of 200m5 × 2 × 0.5 full plastic telephone communication cable;
fig. 7 shows the measurement results of an all-plastic commercial telecommunication cable of 100m5 × 2 × 0.5 gauge;
fig. 8 shows the measurement results of an all-plastic commercial telecommunication cable of 400m5 × 2 × 0.5 gauge.
The specific implementation mode is as follows:
the invention is further described with reference to the following figures and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Term interpretation section: including custom terms, uncommon terms, terms requiring a clear interpretation, references to content, etc.
As introduced in the background art, the prior art has the disadvantages that the cable state analysis method is too complicated, the fault location can be realized only by the platform and the database through the support of a complex algorithm, the background software development difficulty is high, the cable length, the change of the characteristic impedance of the cable and other attribute information cannot be accurately estimated, in order to solve the technical problems, the invention provides a simplified frequency sweep measuring device and a method for estimating cable properties by analyzing the frequency domain characteristics of the cable reflection coefficient measured by the device, the invention only measures the amplitude information of the reflection signal, reduces the complexity of the measuring device and improves the anti-interference capability of the measuring device, the cable length can be estimated accurately by analyzing the frequency domain data, and whether the characteristic impedance of the cable changes or not is judged, so that whether the cable is damaged or not is judged.
A simplified sweep frequency measuring device, hereinafter referred to as measuring device for short, comprising:
the sinusoidal wave signal generating module is configured to generate a frequency-adjustable sinusoidal signal as a transmitting signal source through a DDS technology;
the adjustable power amplification module is configured to adjust the transmitting power of the sine wave frequency sweeping signal generation module according to the actual condition requirement;
the double directional coupler module is configured to perform directional coupling sampling output on the transmitting signal and the reflected signal respectively and input the coupled sampling signals to the corresponding power measurement modules;
the power measurement module is configured to measure and collect the signal power output by the RF switch module;
the connector impedance matching module is configured to form a circuit network with adjustable output side impedance by using transformers with different transformation ratios and matching resistors, so that the circuit network can perform impedance matching on cables with different impedance types;
and the MCU control module is configured to be connected with the sine wave signal generating module, the adjustable power amplifying module and the joint impedance matching module, and is used for scheduling and coordinately controlling the modules so as to monitor the state of the shielding layer of the communication cable.
The dual directional coupler module comprises an input port, a through port, a coupling port 1, a coupling port 2 and an isolation port;
the directional coupler is used for sampling a sweep frequency reflection signal, the sweep frequency emission signal is input through the input port of the directional coupler, the coupling port is used for outputting a sampling signal of the directional coupler for the sweep frequency emission signal and the reflection signal, the through port is used for outputting the sweep frequency emission signal or the input reflection signal passing through the directional coupler, and the isolation port is suspended.
The display module is configured to be an LCD display screen capable of displaying a chart and displaying the frequency sweep measurement result.
The RF switch module, configured as a high-frequency analog switching device of SPDT x 1 type, i.e., a single-pole double-throw switch, allows high-frequency analog signals to pass through.
The load cable is a communication cable to be measured and is connected with the measuring device.
The sweep frequency measurement method based on the device comprises the following steps
(1) Connecting the load cable with the connector impedance matching module, and adjusting the connector impedance matching module to match the output of the detection device with the input impedance of the load cable;
(2) the MCU control module controls the sine wave signal generating module to generate a sine signal with a certain fixed frequency and inputs the sine signal to the adjustable power amplifying module;
(3) the MCU control module controls the adjustable power amplification module to adjust the sine signal to set power (the set power is stored in the MCU module as the transmitting power of the sine signal), and then the sine signal is input into the bi-directional coupler module, the bi-directional coupler module performs coupling sampling on the transmitting signal, the RF switch module is switched to be connected to a coupling port 1 of the bi-directional coupler module, and the sampling signal is input into the power measurement module; transmitting signal main energy to be coupled into a load cable through a bi-directional coupler module and a joint impedance matching module;
(4) the MCU control module controls the power measurement module to measure the input signal power, and after the measurement result is stable, the transmission signal power data measured by the power measurement module is recorded and stored; after the completion, the MCU control module controls the RF switch module to switch to the coupling port 2 of the dual directional coupler module.
(5) After the sinusoidal signal is coupled into the load cable, reflections can be generated at the end of the communication cable or at spatial locations where impedance discontinuities occur; the reflected signal is reversely transmitted along the original path and passes through the joint impedance matching module, the impedance matching action of the joint impedance matching module ensures the normal transmission of the signal, and the signal is effectively prevented from being reflected for multiple times or generating strong oscillation between the module and an impedance mismatch point (generally, a damaged point of a cable shielding layer) to influence the accuracy of a measuring result;
(6) the reflected signal is continuously transmitted to a dual directional coupler module, the module samples and couples and outputs the reflected signal, and then the reflected signal is coupled to a power measurement module through an RF switch module;
(7) the MCU control module controls the power measurement module to measure the input signal power, and after the measurement result is stable, the reflected signal power data measured by the power measurement module is recorded and stored;
(8) the MCU module controls the sine wave signal generation module to generate a sine signal of the next frequency point, and the steps (3) to (7) are repeated; after measuring the data of all the preset frequency points, executing (9);
(9) the MCU module calculates and counts the frequency sweep measurement result, calculates the return loss, the reflection coefficient and the voltage standing wave ratio of the tested load cable at each frequency point, and displays the return loss, the reflection coefficient and the voltage standing wave ratio in a display module in a chart form;
in the step (1), the impedance matching module outputs differential pins, and the connection modes are different according to different types of cables and different cable attributes; for the attribute measurement of a twisted pair in a city telephone communication cable, the differential pin is directly connected with the twisted pair; for the condition of measuring the property of the shielding layer of the urban telephone communication cable, one of the differential pins needs to be connected with the shielding layer of the cable, and the other differential pin needs to be connected with any core wire; for a coaxial communication cable, the differential pins are respectively connected with the shielding layer and the central axis;
in the step (5), after the signal is coupled into the load cable, reflection is generated due to impedance mismatch at a place where impedance between the cable shielding layer and the core wire is changed (including a cable end), and the reflected signal is transmitted to the connector impedance matching module along the load cable, then transmitted to the dual directional coupler module, and finally transmitted to the power measurement module through the RF switch module to perform power measurement.
In the step (8), the measuring device sets different sweep frequency ranges and sweep frequency intervals for different types of communication cables in different environments, and stores the setting information to the MCU control module, so that the measuring device can conveniently perform automatic sweep frequency measurement;
in the step (9), the calculating and counting of the sweep frequency measurement result means that three common reflection parameters, namely a corresponding reflection coefficient, a voltage standing wave ratio and a return loss, can be calculated by measuring the powers of the transmitted signal and the reflected signal and combining the parameters of the directional coupler; the specific conversion formula can refer to relevant radio frequency textbooks.
A method for estimating cable attribute by sweep frequency reflection coefficient mainly comprises the following steps:
(1) firstly, carrying out frequency sweep measurement on a communication cable with a known length to obtain a return loss frequency spectrum of the cable (figures 3 and 4); the measurement result shows that the frequency spectrum of the return loss is not a straight line, but shows 'wave-shaped' change, and the total trend of the return loss is increased along with the gradual increase of the frequency; in the frequency spectrum, recording the number of complete waves (small digits can be reserved) in the return loss frequency spectrum corresponding to the cable with the length, and calculating the number of 'waves' corresponding to the cable with the unit length, and recording the number as N0;
(2) performing frequency sweep measurement on other cables with unknown lengths, similarly obtaining a frequency spectrum of return loss, and counting the number of waves in the frequency spectrum (marked as N), so that the estimated value of the length of the cable is as follows: L-N/N0 (unit length); as in fig. 3 and 5, fig. 4 and 6;
(3) performing frequency sweep measurement on the deployed intact communication cable, and recording standard measurement data as a reference for later judging whether the impedance characteristic of the cable is abnormal;
(4) the method comprises the steps that sweep frequency measurement is carried out on a communication cable in operation periodically, and if the difference between a measured return loss frequency spectrum and a reference frequency spectrum is too large, the impedance characteristic of the communication cable is changed, and the cable is possibly damaged or abnormal; the maintenance is required to be carried out in time;
in the step (1), the swept frequency reflection parameters include three parameters of reflection coefficient, voltage standing wave ratio and return loss, and taking return loss as an example, as shown in fig. 3 to 8, the sweep frequency reflection parameters are sweep frequency measurement results of return loss of the following communication cables by using a sweep frequency measurement device;
in the step (1), the return loss frequency spectrum shows 'wave-shaped' change, and the explanation in a macroscopic angle is as follows: in the transmission process of the transmission signal in the communication cable, the phase of the transmission signal is gradually delayed due to the existence of the distributed inductance and capacitance of the cable; because the space structure of the cable is relatively fixed, and the distributed inductance and the distributed capacitance can also be regarded as inherent properties of the cable, the speed of signal phase delay is also fixed for the same cable structure;
when the reflection occurs when the transmission is transmitted to the tail end of the cable, a reflection signal with the same frequency and different phase with the transmission signal is formed; the reflected signal and the transmitted signal are subjected to wave superposition in the transmission process, partial standing waves are formed due to different phases, energy flux density of the transmitted and reflected electromagnetic waves is uneven, energy coupling efficiency is reduced, and the frequency spectrum of return loss is changed in a wave shape along with the change of the phase difference of the transmitted signal and the reflected signal;
from the perspective of signal measurement, the change rule of the return loss frequency spectrum is the reflection of the phase information of the sweep frequency signal in the signal amplitude information due to the superposition of waves, which is equivalent to the indirect measurement of the phase information of the sweep frequency signal; this is also the theoretical basis on which the method can estimate the cable length.
In an exemplary embodiment of the present application, as shown in fig. 1, a device for detecting a state of a shielding layer of a communication cable includes an MCU control module, a display module, a sine wave signal generating module, an adjustable power amplifying module, a connector impedance matching module, a bi-directional coupler module, an RF switch module, and a power measuring module.
The sine wave signal generation module adopts a highly integrated CMOS complete digital frequency synthesizer, and mainly comprises the following components: a high-speed DDS module, a frequency setting register and a high-speed digital-to-analog converter (DAC); reference model: AD9851 by ADI.
The adjustable power amplification module mainly comprises an adjustable gain amplifier (VGA), a power amplifier (HPA) and a peripheral circuit thereof, wherein the VGA has a reference model: AD8338 from ADI corporation; HPA reference model: ADA4870 from ADI;
and the joint impedance matching module consists of a matching transformer and peripheral matching resistors, capacitors and inductance elements thereof. Matching basic parameters of the transformer: the primary side and the secondary side have adjustable transformation ratio of 1-16, the input impedance of the primary side is 50 omega within a frequency range of 300Hz-10MHz, and the upper limit threshold of transmission power is 5W;
the double directional coupler module is composed of a bidirectional directional coupler and an attenuator network. Basic parameters of the directional coupler: insertion loss <0.5dB, supporting frequency range 300K-10MHz, interface impedance: 50 omega;
the power measurement module adopts AD8310 of ADI company, and has wide dynamic range, high measurement precision and wide support frequency band.
The RF switch module and the radio frequency switch are used for switching an input signal channel of the power measurement module, and the function of respectively sampling the power of the transmitted signal and the reflected signal by one power measurement module can be realized through the operation of the module. Reference model: ADG918, ADG 919; the supporting frequency band is wide, the isolation degree is high, and the crosstalk is small;
the display module adopts a common industrial display screen, has low power consumption and is convenient for the operation of portable equipment;
device control method (as shown in fig. 1):
1. the device can complete simple closed-loop control;
1) initialization of a detection device: the MCU module reads a preset minimum value A, a preset maximum value B and a preset frequency interval x of a frequency sweeping range; (ii) a The MCU control module sends a power-on instruction to the sine wave signal generation module, then sends initial sine wave frequency control information, and the control module enters a state to be output; the MCU control module sends a power-on instruction to the adjustable power amplification module, then sends an initial signal power amplification factor as the lowest amplification factor, and the control module enters a standby working state; the MCU control module controls the connector impedance matching module to perform initial impedance matching setting; the MCU control module controls the power-on and initialization of the power measurement module to enable the power measurement module to enter a standby working state; the MCU control module controls the display module to be powered on and initialized so as to enter an initial interface; powering on and initializing the RF switch module, and switching to a connection transmitting signal (coupled port 1) and a power measuring module by default;
2) delaying for a period of time, after the running state of each module of the device is stable, the MCU module controls the sine wave signal generation module and the adjustable power amplification module to start outputting, and simultaneously controls the power measurement module to start working, receives the signal transmitted by the RF switch, measures the power, and sends the result to the MCU control module;
3) delaying for a period of time, and after the power measurement of the transmitted signal is finished, controlling the RF switch module to be switched to a connection reflection signal (a coupling port 2) and a power measurement module by the MCU module; the power measurement module is controlled to carry out power measurement on the signal transmitted by the RF switch module, and the result is sent to the MCU control module;
4) the MCU control module analyzes and calculates the received power information to obtain the return loss (or reflection coefficient and voltage standing wave ratio) at the frequency point, and then stores the measurement conditions of the measurement, including the frequency and the power of the transmitted signal, the power of the reflected signal and the return loss value;
5) and (3) judging: when the frequency f measured this time is less than B, the MCU module controls the sine signal generation module to adjust the output frequency to be f + x; repeating (2) - (5); when f is B, executing (6);
6) the MCU control module controls the display module to display the measured return loss frequency spectrum;
2. the device and the display module can complete the open-loop control of external manual input;
1) the display module can send a fixed frequency measurement command which is manually input to the MCU control module, the MCU control module controls the sine wave signal generation module to adjust the frequency of the sine signal according to frequency information in the command, and then the steps (2) to (4) in the control method 1 are executed;
the display module can manually input a fixed power amplification factor command to the MCU control module, the MCU control module controls the adjustable power amplification module to adjust the power amplification factor of the sinusoidal signal according to the output power amplification factor information in the command, and then the steps (2) to (4) in the control method 1 are executed.
Example verification:
as shown in fig. 3 and 4, the number of "waves" in the echo loss spectrum measured in the same frequency band of two coaxial communication cables with the same length is about 2.5, and parameters can be calculated: n0 is 2.5/35 is 0.0714/m;
as shown in FIG. 5, the number of the waves is about 14, and the corresponding cable length L ≈ 14/N0 ≈ 196m is calculated; substantially corresponding to the actual cable length;
through the method, the verification can be sequentially carried out on the graphs 6-8, and the calculation results are consistent with the actual cable length within the error range.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (7)
1. A swept frequency measurement device, comprising:
the sinusoidal wave signal generating module is configured to generate a frequency-adjustable sinusoidal signal as a transmitting signal source through a DDS technology;
the adjustable power amplification module is configured to adjust the transmitting power of the sine wave frequency sweeping signal generation module according to the actual condition requirement;
the connector impedance matching module is configured to form a circuit network with adjustable output side impedance by using transformers with different transformation ratios and matching resistors, so that the circuit network can perform impedance matching on cables with different impedance types;
it is characterized by also comprising: the double directional coupler module is configured to perform directional coupling sampling output on the transmitting signal and the reflected signal respectively and input the coupled sampling signals to the corresponding power measurement modules;
the power measurement module is configured to measure and collect signal powers output by different output ports of the dual directional coupler module;
the first coupling port and the second coupling port of the dual directional coupler module are connected with the MCU control module and the power measurement module through the RF switch module, and switching is realized through the RF switch module, or the two power measurement modules are respectively connected with the first coupling port and the second coupling port;
the MCU control module is configured to be connected with the sine wave signal generating module, the adjustable power amplifying module, the power measuring module and the connector impedance matching module, and is used for scheduling and coordinately controlling the modules so as to monitor the state of a shielding layer of a communication cable; the MCU control module calculates and counts the frequency sweep measurement result, calculates the return loss, the reflection coefficient and the voltage standing wave ratio of the measured load cable at each frequency point, and displays the return loss, the reflection coefficient and the voltage standing wave ratio in a display module in a chart form;
the dual directional coupler module comprises an input port, a pass-through port, a first coupling port, a second coupling port and an isolation port;
the directional coupler is used for sampling a sweep frequency reflection signal, the sweep frequency emission signal is input from the input port of the directional coupler, the first coupling port and the second coupling port are used for outputting sampling signals of the directional coupler for the sweep frequency emission signal and the reflection signal, the through port is used for outputting the sweep frequency emission signal or the input reflection signal passing through the directional coupler, and the isolation port is suspended;
estimating the cable attribute through the sweep return loss is to perform sweep measurement on a communication cable with a known length to obtain the return loss frequency spectrum of the cable, record the number of complete waves in the return loss frequency spectrum corresponding to the cable with the length, and calculate the number of curves in the return loss frequency spectrum corresponding to the cable with the unit length to fluctuate, and record the number as N0; carrying out frequency sweep measurement on other cables with unknown lengths, similarly obtaining a frequency spectrum of return loss, counting the number of curves in the frequency spectrum which fluctuate, marking as N, and calculating the length estimated value L of the cable which is N/N0; performing frequency sweep measurement on the deployed intact communication cable, and recording standard measurement data as a reference for later judging whether the impedance characteristic of the cable is abnormal; and periodically carrying out frequency sweep measurement on the communication cable in operation, and if the difference between the measured return loss frequency spectrum and the reference frequency spectrum exceeds a set value, indicating that the impedance characteristic of the communication cable is changed and the cable is possibly damaged or abnormal.
2. A frequency sweep measuring method based on the apparatus as claimed in claim 1, characterized in that:
the method comprises the following steps:
(1) connecting the load cable with the connector impedance matching module, and adjusting the connector impedance matching module to match the output of the detection device with the input impedance of the load cable;
(2) the MCU control module controls the sine wave signal generating module to generate a sine signal with a certain fixed frequency and inputs the sine signal to the adjustable power amplifying module;
(3) the MCU control module controls the adjustable power amplification module to adjust the sine signal to set power and inputs the sine signal to the bi-directional coupler module, the bi-directional coupler module performs coupling sampling on a transmitting signal, the RF switch module is switched to be connected to a first coupling port of the bi-directional coupler module, and a sampling signal is input to the power measurement module; transmitting signal main energy to be coupled into a load cable through a bi-directional coupler module and a joint impedance matching module;
(4) the MCU control module controls the power measurement module to measure the input signal power, and after the measurement result is stable, the transmission signal power data measured by the power measurement module is recorded and stored; after the completion, the MCU control module controls the RF switch module to be switched to a second coupling port of the dual directional coupler module;
(5) after the sinusoidal signal is coupled into the load cable, reflections can be generated at the end of the communication cable or at spatial locations where impedance discontinuities occur; the reflected signal is transmitted along the original path in a reverse direction and passes through the connector impedance matching module;
(6) the reflected signal is continuously transmitted to a dual directional coupler module, the module samples and couples and outputs the reflected signal, and then the reflected signal is coupled to a power measurement module through an RF switch module;
(7) the MCU control module controls the power measurement module to measure the input signal power, and after the measurement result is stable, the reflected signal power data measured by the power measurement module is recorded and stored;
(8) the MCU module controls the sine wave signal generation module to generate a sine signal of the next frequency point, and the steps (3) to (7) are repeated; after measuring all data of the preset frequency points, executing (9);
(9) the MCU module calculates and counts the frequency sweep measurement result, calculates the return loss, the reflection coefficient and the voltage standing wave ratio of the tested load cable at each frequency point, and displays the return loss, the reflection coefficient and the voltage standing wave ratio in a display module in a chart form;
a method for estimating cable properties via swept frequency return loss, comprising:
(I) firstly, carrying out sweep frequency measurement on a communication cable with a known length to obtain a return loss frequency spectrum of the cable, recording the number of complete waves in the return loss frequency spectrum corresponding to the cable with the known length, and calculating the number of curves in the return loss frequency spectrum corresponding to the cable with the unit length to fluctuate, and recording the number as N0;
(II) carrying out frequency sweep measurement on other cables with unknown lengths, similarly obtaining a frequency spectrum of return loss, counting the number of curves in the frequency spectrum which fluctuate, marking the number as N, and calculating the length estimation value L of the cable to be N/N0;
(III) carrying out frequency sweep measurement on the deployed intact communication cable, and recording standard measurement data as a comparison reference for judging whether the impedance characteristic of the cable is abnormal or not;
(IV) periodically carrying out frequency sweep measurement on the communication cable in operation, and if the difference between the measured return loss spectrum and the reference spectrum exceeds a set value, indicating that the impedance characteristic of the communication cable is changed and the cable is possibly damaged or abnormal.
3. A frequency sweep measuring method as claimed in claim 2, characterized by: in the step (1), the impedance matching module outputs differential pins, and the connection modes are different according to different types of cables and different cable attributes; for the attribute measurement of a certain twisted pair in a communication cable, a differential pin is directly connected with the twisted pair; for the condition of measuring the property of the shielding layer of the communication cable, one of the differential pins needs to be connected with the shielding layer of the cable, and the other differential pin needs to be connected with any core wire; for coaxial communication cables, the differential pins are connected to the shield and the central axis, respectively.
4. A frequency sweep measuring method as claimed in claim 2, characterized by: in the step (5), after the signal is coupled into the load cable, where the impedance between the cable shielding layer and the core wire is changed, the impedance mismatch generates a reflection, and the reflected signal is transmitted to the connector impedance matching module along the load cable, then transmitted to the dual directional coupler module, and finally transmitted to the power measurement module through the RF switch module for power measurement.
5. A frequency sweep measuring method as claimed in claim 2, characterized by: in the step (8), the measuring device sets different sweep frequency ranges and sweep frequency intervals for different types of communication cables in different environments, and stores the setting information to the MCU control module for automatic sweep frequency measurement.
6. A frequency sweep measuring method as claimed in claim 2, characterized by: in the step (9), three common reflection parameters, namely a corresponding reflection coefficient, a voltage standing wave ratio and a return loss, can be calculated through the measured powers of the transmitted signal and the reflected signal, so that the calculation and statistics of the frequency sweep measurement result are realized.
7. A frequency sweep measuring method as claimed in claim 2, characterized by:
in the step (I), from the perspective of signal measurement, the change rule of the return loss spectrum is the reflection of the phase information of the sweep frequency signal in the amplitude value information due to the superposition of the wave, which is equivalent to indirectly measuring the phase information of the sweep frequency signal.
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| CN108445291A (en) * | 2018-03-14 | 2018-08-24 | 哈尔滨工业大学 | A kind of cable quality of production control method based on back scattering inversion technique |
| KR20210066892A (en) * | 2018-10-04 | 2021-06-07 | 비아셋, 인크 | Time Division Duplex (TDD) Antenna System |
| CN109541391A (en) * | 2018-10-10 | 2019-03-29 | 山东康威通信技术股份有限公司 | A kind of low-power consumption cable shield on-Line Monitor Device, monitoring system and method |
| CN110161333B (en) * | 2019-05-23 | 2021-03-02 | 上海微小卫星工程中心 | Isolator reverse power withstand test system and method |
| CN111610370A (en) * | 2019-05-23 | 2020-09-01 | 青岛鼎信通讯股份有限公司 | 10kV line impedance detection device |
| CN110261739B (en) * | 2019-07-29 | 2021-11-09 | 哈尔滨工业大学 | Cable soft fault positioning device and positioning method |
| CN111521911B (en) * | 2020-05-21 | 2021-07-09 | 山东信通电子股份有限公司 | Intelligent monitoring method and equipment for power transmission line |
| CN113805101A (en) * | 2021-07-14 | 2021-12-17 | 国网江苏省电力有限公司电力科学研究院 | Cable cross interconnection system connection state testing method and testing device |
| CN116742432B (en) * | 2023-08-15 | 2023-10-24 | 西安普用电子科技有限公司 | Interface universality adapting method and system for realizing cable assembly based on negative feedback |
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| CN105301444A (en) * | 2015-10-14 | 2016-02-03 | 云南电网有限责任公司普洱供电局 | Single-port detection-based cable fault locating device |
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