Low-frequency and very-low-frequency signal monitoring method and device

Abstract

The embodiment of the invention provides a very low frequency signal monitoring method and device, and the device consists of a signal receiving unit (1), a signal measurement unit (2), a parameter regulation and control unit (3), and a main control unit (4). And the parameter regulation and control unit (3) can respectively set parameters of each working component in the signal receiving unit (1) and the signal measuring unit (2) according to the center frequency and bandwidth list of the main control unit (4), and can control a turntable (5) of an antenna coil (13) to align to the strongest direction of a synchronous measurement signal, so that measurement and data storage of a specific very low frequency signal in the bandwidth are realized. The method is characterized in that collection of monitoring signals and measurement of signal parameters are realized based on synchronization characteristics of known signals, interference signals can be well distinguished, and the accuracy of monitoring data is guaranteed.

Description

Technical Field

[0001] This application relates to the field of wireless communication, and in particular to a method and process for monitoring very low frequency signals. Background Technology

[0002] In very low frequency (VLF) wireless communication systems, the communication quality of the wireless channel varies significantly at different times due to factors such as solar activity in the atmosphere. Sometimes the signal strength at night can be about 10 dB higher than during the day. Therefore, a few points in time cannot represent the signal quality for the entire day; long-term continuous monitoring is necessary to understand the patterns of VLF signal propagation and interference. Currently, the measurement methods and devices proposed in relevant literature mainly include:

[0003] Patent CN116388899A, entitled "A Method for Measuring Background Noise in Communication Channels," describes a method that involves switching the communication device from a first frequency (the frequency used in the original transmission and reception process) to a second frequency (the frequency at which the background noise is to be tested) within a short inter-frame interval after the communication device transmits data, opening the receiving path of the communication device to sample the signal; after sampling, switching the frequency of the communication device back to the first frequency; and calculating the energy of the sampled signal as the background noise.

[0004] Patent CN117375742A, entitled "Portable High-Precision Shortwave Monitoring and Direction Finding System," proposes a portable high-precision shortwave monitoring and direction finding system. The system comprises a portable shortwave monitoring and direction finding device, a shortwave monitoring and direction finding antenna, a display and control terminal, display and control software, a BeiDou antenna, and a network access unit, enabling direction finding and reconnaissance functions. The system software employs an adaptive noise threshold estimation and signal extraction method based on monitoring data, achieving automatic noise threshold setting and intelligent signal extraction, and exhibiting adaptive analysis characteristics for different electromagnetic environments, different time periods, and different frequency bands.

[0005] The above methods generally use broadband signal monitoring, which cannot distinguish whether the monitored signal is interference or a useful signal. This method is based on the synchronization characteristics of known signals to achieve accurate differentiation of monitored signals and measurement of signal parameters. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of narrowband very low frequency band adaptation in existing technologies, and to provide a very low frequency signal monitoring method and device. The above invention is achieved through the following technical solutions:

[0007] 1. A very low frequency signal monitoring device of the present invention, such as Figure 3 As shown, it is characterized by comprising the following components:

[0008] (1) Signal receiving unit (1), whose main function is to select different tuning network (6) and impedance matching transformer (7) parameters according to the center frequency. The receiving antenna converts electromagnetic waves in free space into electrical signals. The parameters of the tuning network are adjusted by the host computer to make the center frequency of the receiving antenna consistent with the measurement frequency. The impedance matching transformer is set according to the tuning network parameters to achieve the maximum power transmission of the signal to the measurement unit. The turntable (5) rotates at a specific angle according to the settings.

[0009] (2) Signal measurement unit (2) mainly consists of five components: an adjustable attenuator, a filter, an amplifier, an AD sampler, and a digital downconversion synthesizer (DDC). The parameters of the five components can be adjusted according to the set parameters.

[0010] (3) Parameter control unit (3) The main function is to calculate the control parameters of the signal measurement unit and the signal receiving unit according to the center frequency and bandwidth of the main control unit, realize the parameter configuration of the repeater (5), tuning network (6) and impedance matching transformer (7) in the antenna receiving unit, and realize the parameter configuration of the attenuator (8), filter (9), amplifier (10), AD (11) sampler and digital downconversion synthesis DDC (12) in the measurement unit.

[0011] (4) The main control unit (4) is responsible for sending the center frequency and bandwidth to the parameter control unit according to the measurement sequence, and receiving the IQ data from the measurement unit, performing spectrum analysis and saving the measurement data.

[0012] 2. Signal measurement unit (2), characterized in that:

[0013] (1) The function of attenuator (8) is to attenuate large signals so that they are within the linear region of the amplifier.

[0014] (2) The filter (9) filters the input signal, filtering out noise and interference signals outside the measurement bandwidth.

[0015] (3) Amplifier (10) is a low-noise linear amplifier, which amplifies small signals to a suitable range for AD sampling.

[0016] (4) The AD sampler (11) is used to sample and convert analog signals into digital signals according to the sampling rate. For signal matching, the sampling rate is generally set to an integer multiple of the sampled carrier signal.

[0017] (5) The digital DDC (12) implements digital downsampling and downconversion functions. Internally, it first performs Hilbert transformation on the sampled digital signal to obtain a complex signal, and then downconverts the signal to the baseband frequency or intermediate frequency to obtain I / Q sampling signals.

[0018] 3. Parameter control unit (3), characterized in that:

[0019] Based on the center frequency and bandwidth of the signal, the access parameters of the digitally controlled potentiometer, the adjustable capacitor module and the turns ratio of the impedance matching transformer in the tuning network are set to control the rotation speed and angle of the turntable (5), and the appropriate settings of the attenuator (8), filter (9), amplifier (10), AD (11) sampler and digital downconversion synthesizer (DDC) (12) are selected.

[0020] in,

[0021] (1) A digital potentiometer is a new type of CMOS digital and analog mixed signal processing integrated circuit. The resistance value is adjusted by numerical control, and the resistor network is designed according to the bandwidth.

[0022] (2) The programmable capacitor module uses a high-precision capacitor network in conjunction with the switching of multiple relays to achieve capacitor regulation. The capacitor network is designed according to the frequency.

[0023] (3) Impedance matching transformer (7) The turns ratio is designed based on the antenna output impedance and the load circuit input impedance. The primary side of the transformer has multiple access points, and the turns ratio can be adjusted by switching the access points.

[0024] (4) The turntable (5) is a CNC turntable. The encoder detects the rotation angle of the turntable spindle and converts it into a digital signal, which is then transmitted to the controller for processing. The rotation angle and speed of the turntable are controlled by the program.

[0025] (5) The attenuator (8) can be set with attenuation level n. By changing the internal attenuation resistor network, the attenuation can be set in units of n*3dB, where n = 0, 1, ... 10.

[0026] (6) The filter (9) can be set to high-pass, low-pass, or band-pass filtering. The system hardware has built-in low-pass filter L, high-pass filter M, and band-pass filter N. Users can select the appropriate filter according to the actual situation. The high-pass filter range is [f1,∞], the low-pass filter range is [0,f2], and the band-pass filter range is [f1,f2], where f1 and f2 can be set according to the actual signal.

[0027] (7) The input of amplifier (10) is the amplification factor. The value of the amplifier can be changed by setting the peripheral circuit. Due to the linear region limitation, it is necessary to calculate that the input signal is within the linear region. This can be achieved by the AGC automatic gain control circuit.

[0028] (8) The sampling rate of the AD sampler (11) can be flexibly set as AD sampling rate = AD sampling clock frequency / N, where N is the frequency division coefficient.

[0029] (9) The digital DDC (12) can set the downsampling rate.

[0030] 4. A very low frequency signal monitoring method according to the present invention, which realizes the acquisition of monitoring signals and the measurement of signal parameters based on the synchronization characteristics of known signals, and includes the following steps:

[0031] Step 1: The main control unit (4) sends the center frequency and bandwidth information to the parameter control unit (3), which calculates the parameter settings of each component in the signal receiving unit (1) and the signal measurement unit (2).

[0032] Step 2: The parameter control unit (3) sets the parameters of each component in the signal receiving unit (1) and the signal measurement unit (2), including the turntable (5) of the antenna coil, the tuning network (6), the impedance matching transformer (7), and the unit parameters of the attenuator (8), the filter (9), the amplifier (10), the AD (11) sampler, the digital downconversion synthesizer (DDC) (12), etc., and turns on the receiving signal monitoring.

[0033] Step 3: The parameter control unit (3) controls the turntable (5) to adjust the antenna direction angle in units of 1 degree, while performing frequency domain transformation on the received signal, calculating the power spectral density, monitoring the spectrum of the signal on the center frequency and bandwidth, searching for the position with the largest power spectrum at the center frequency, and recording the position information of that angle.

[0034] Step 4: At this angle position, the main control unit (4) performs correlation calculations between the received signal and the known synchronization sequence to locate the starting time position of the signal and demodulate the synchronized signal.

[0035] Step 5: For signals successfully demodulated using the synchronous sequence, identify them as the signals to be measured. First, perform spectral analysis to obtain the power spectral density curve. Based on the center frequency and bandwidth, integrate the signal power spectral density within the bandwidth as the signal power S (in dBm), and calculate the attenuation D (in dB, its value is: attenuation factor - amplification factor) after front-end circuit synthesis. The final actual signal power is SD (in dBm). Based on the power spectral density curve, calculate the power spectral density N0 outside the bandwidth. Multiply the power spectral density by the bandwidth to obtain the noise power N (in dBm), and the final actual signal power is ND (in dBm). Calculate the signal signal-to-noise ratio SNR = SN (in dBm), and save the acquisition time, center frequency and bandwidth, S, N, SNR, and the IQ data of the acquired waveform points as monitoring record data.

[0036] Wherein, the attenuation D of the front-end circuit = attenuator gain (dB) + filter equivalent attenuation gain (dB) - amplifier gain (dB) = AD sampling signal power.

[0037] Step 6: For signals that are not successfully demodulated, the detected signals are determined to be interference signals. The main control unit (4) notifies the parameter control unit (3) to control the turntable (5) to rotate 90 degrees counterclockwise from the position where the signal is strongest to avoid interference signals and perform secondary demodulation as in step 5. If demodulation is successful, the acquisition time, center frequency and bandwidth, S, N, and SNR are saved as feature data.

[0038] The detailed method for monitoring very low frequency signals is described below:

[0039] According to the measurement center frequency and bandwidth list, such as (f1,B1), (f2,B2)...(fn,Bn), the measurement is performed in sequence. The parameter adjustment unit parameters are set and converted into the settings of attenuator, filter, amplifier, AD sampler, and digital downconverter synthesizer (DDC).

[0040] Alternatively, the AGC (Automatic Gain Control) mode can be selected. In this mode, the AGC unit will automatically select the appropriate control parameters to keep the gain within the linear range of the LNA and ensure that the signal is greater than the minimum acquisition voltage value of the AD.

[0041] Because the signal truncated during the FFT transformation, a window function needs to be applied to the time-domain signal to smooth it before performing the FFT. Assuming an N-point FFT, then x(nT) s )=x in (nT s )×W(n), where W is the discrete point of the window function.

[0042] According to the discrete FFT transform formula:

[0043]

[0044] Find:

[0045]

[0046] then:

[0047]

[0048] N is the number of FFT points, and k is the frequency index.

[0049] IQ signal acquisition is performed, and windowing is applied to the corresponding number of data points. FFT operation is then performed to calculate the noise power value in dBm at the center frequency within the bandwidth range. The relevant acquisition time, center frequency and bandwidth, signal power, noise power, signal-to-noise ratio, and IQ data of the acquired waveform points are saved.

[0050] Beneficial effects

[0051] This invention has the following innovative features compared to existing technologies:

[0052] (1) The main control unit (4) controls the signal receiving unit (1) and the signal measurement unit (2), which automatically searches for the direction of the strongest signal by rotating the turntable (5) antenna direction, and combines the signal synchronization sequence demodulation mechanism to effectively distinguish between signals and interference, and realize the measurement and storage of signal power, noise power, signal-to-noise ratio and useful signal waveform.

[0053] (2) Parameter control unit (3) According to the center frequency and bandwidth sequence, the peripheral center frequency and bandwidth are flexibly and automatically configured, and the receiving antenna and measuring circuit are configured to rotate the antenna coil according to the very low frequency center frequency and bandwidth, so as to accurately match the signal to the range to be measured, so as to meet the needs of very low frequency signal monitoring. Attached Figure Description

[0054] Figure 1 A diagram illustrating a signal sampling and processing process provided by this invention;

[0055] Figure 2 Another flowchart for center frequency setting and automatic measurement provided by the present invention;

[0056] Figure 3 A diagram of another very low frequency signal monitoring device provided by the present invention; Detailed Implementation

[0057] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application. Furthermore, the embodiments and features described herein can be combined with each other unless otherwise specified.

[0058] 1 Signal receiving unit

[0059] Its main components include a directional receiving antenna coil (13), a turntable for the antenna coil (5), a tuning network (6), and an impedance matching transformer (7). Its implementation process is as follows: Figure 1 As shown.

[0060] in,

[0061] The directional receiving antenna coil (13) is a magnetic core loop antenna, which is made by tightly winding enameled wire around a manganese zinc ferrite rod with a length of 500 mm and an aspect ratio of 10 to 20. The inductance of the coil is in the range of 1 mH to 2 mH.

[0062] The turntable (5) for the antenna coil is a CNC turntable. The encoder detects the rotation angle of the turntable spindle and converts it into a digital signal, which is then transmitted to the controller for processing. The rotation angle and speed of the turntable are controlled by the PC program. For example, if the turntable is set to rotate at 30° intervals every 5 minutes, one rotation is equivalent to one hour, which is one working cycle.

[0063] The main components of the tuning network (6) are a digitally controlled potentiometer and an adjustable capacitor module. The structure and capacitance distribution of the adjustable capacitor network are determined by the antenna coil parameters and the set test frequency using the resonance formula. The calculation yielded the result.

[0064] The impedance matching transformer (7) performs impedance matching between the antenna and the load circuit. The output impedance of the antenna after passing through the tuning network is Z. O The input impedance of the load circuit is Z. L The transformer turns ratio design value is The primary coil of the matching transformer is led out to multiple access points to meet the matching of different antenna output impedances and load circuits. The switching of access points, i.e. the adjustment of the turns ratio, is completed by software control of the peripheral circuit.

[0065] 2 Signal Measurement Unit

[0066] Its main components include an attenuator (8), a filter (9), an amplifier (10), an AD (11) sampler, and a digital down-conversion synthesizer (DDC) (12). Its implementation process is as follows: Figure 2 As shown.

[0067] The functions of each processing unit are implemented as follows:

[0068] The attenuator is a selectable attenuator (8), which can be set to attenuation in units of n*3dB, where n = 1..8.

[0069] The filter (9) can be set to low-pass, high-pass or band-pass filtering, with a filtering range of [f1, f2], where f1 and f2 can be set according to the actual signal.

[0070] The amplifier (10) LNA is a low-noise linear amplifier. The amplifier value can be changed by setting the value, which ranges from 3 to 10 dB. The purpose is to amplify small signals.

[0071] An AD(11) sampler can sample analog signals and convert them into digital signals at a certain sampling rate. For matching purposes, the sampling rate is generally set to an integer multiple of the sampled carrier signal.

[0072] The digital downconversion synthesis DDC(12) realizes the functions of digital downsampling and downconversion. First, Hilbert transformation is performed to form a complex signal, and then the signal is downconverted to the baseband frequency or intermediate frequency. The output format is two-way IQ signal.

[0073] 3. Parameter control unit (3)

[0074] Based on the center frequency and bandwidth of the signal, the access parameters of the digitally controlled potentiometer, the adjustable capacitor module and the turns ratio of the impedance matching transformer in the tuning network are set to control the rotation speed and angle of the turntable (5), and the settings of the appropriate attenuator (8), filter (9), amplifier (10), AD (11) sampler and digital downconversion synthesizer (DDC) (12) are selected.

[0075] in,

[0076] A digital potentiometer is a new type of CMOS digital-analog mixed signal processing integrated circuit. It adjusts the resistance value through numerical control. The corresponding resistance value is calculated based on antenna parameters, test center frequency, bandwidth, etc. The parameter control unit can control the resistance to adjust the resistance value under the corresponding test parameter conditions.

[0077] The programmable capacitor module uses a high-precision capacitor network in conjunction with the switching of multiple relays to achieve capacitor adjustment. When the antenna winding inductance is 2mH and the test center frequency is f = [10kHz, 12kHz, 14kHz, 16kHz…28kHz, 30kHz], the corresponding capacitance value is C = [126nF, 88nF, 75nF, 49nF…16nF, 14nF]. The parameter control unit can control the capacitor network to achieve the switching of the above values.

[0078] 4. Very Low Frequency Signal Monitoring Method

[0079] A series of center frequencies and bandwidths are set in the software, and the algorithm dynamically sets the peripheral hardware to the corresponding center frequency based on these settings, and enables noise power calculation.

[0080] Based on the settings, the signal power of the antenna interface is calculated equivalently.

[0081] Specific embodiments of the present invention have been described above. Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing this application.

[0082] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A very low frequency (VLF) signal monitoring method, which acquires the monitoring signal and measures the signal parameters based on the synchronization characteristics of a known signal, and includes the following steps: Step 1: The main control unit (4) sends the center frequency and bandwidth information to the parameter control unit (3), which calculates the parameter settings of each component in the signal receiving unit (1) and the signal measurement unit (2). Step 2: The parameter control unit (3) sets the parameters of each component in the signal receiving unit (1) and the signal measurement unit (2), including the turntable (5) of the antenna coil, the tuning network (6), the impedance matching transformer (7), and the unit parameters of the attenuator (8), the filter (9), the amplifier (10), the AD (11) sampler, the digital downconversion synthesizer (DDC) (12), etc., and turns on the receiving signal monitoring. Step 3: The parameter control unit (3) controls the turntable (5) to adjust the antenna direction angle in units of 1 degree, while performing frequency domain transformation on the received signal, calculating the power spectral density, monitoring the spectrum of the signal on the center frequency and bandwidth, searching for the position with the largest power spectrum at the center frequency, and recording the position information of that angle. Step 4: At this angle position, the main control unit (4) performs correlation calculations between the received signal and the known synchronization sequence to locate the starting time position of the signal and demodulate the synchronized signal. Step 5: For signals that have been successfully demodulated in the synchronization sequence, determine them as the signals that need to be measured, perform spectral analysis on them, and obtain the power spectral density curve. Based on the center frequency and bandwidth, the integrated power of the signal power spectral density within the bandwidth is taken as the signal power S (unit: dBm), and the attenuation D after the front-end circuit is synthesized is calculated (unit: attenuation factor - amplification factor). Finally, the actual signal power is SD (unit: dBm). Based on the power spectral density curve, calculate the power spectral density N0 outside the bandwidth. Multiply the power spectral density by the bandwidth to obtain the noise power N (in dBm). Finally, the actual signal power is ND (in dBm). Calculate the signal-to-noise ratio SNR = SN (in dBm), and save the acquisition time, center frequency, bandwidth, S, N, SNR, and the IQ data of the acquired waveform points as monitoring and recording data. Wherein, the attenuation D of the front-end circuit = attenuator gain (dB) + filter equivalent attenuation gain (dB) - amplifier gain (dB) = AD sampling signal power. Step 6: For signals that are not successfully demodulated, the detected signals are determined to be interference signals. The main control unit (4) notifies the parameter control unit (3) to control the turntable (5) to rotate 90 degrees counterclockwise from the position where the signal is strongest to avoid interference signals and perform secondary demodulation as in step 5. If demodulation is successful, the acquisition time, center frequency and bandwidth, S, N, and SNR are saved as feature data.

2. A very low frequency signal monitoring device, characterized in that, It includes the following components: (1) Signal receiving unit (1), whose main function is to select different tuning network (6) and impedance matching transformer (7) parameters according to the center frequency. (2) Signal measurement unit (2) mainly consists of five components: an adjustable attenuator, a filter, an amplifier, an AD sampler, and a digital downconversion synthesizer (DDC). The parameters of the five components can be adjusted according to the set parameters. (3) Parameter control unit (3) The main function is to calculate the control parameters of the signal measurement unit and the signal receiving unit according to the center frequency and bandwidth of the main control unit, realize the parameter configuration of the repeater (5), tuning network (6) and impedance matching transformer (7) in the antenna receiving unit, and realize the parameter configuration of the attenuator (8), filter (9), amplifier (10), AD (11) sampler and digital downconversion synthesis DDC (12) in the measurement unit. (4) The main control unit (4) is responsible for sending the center frequency and bandwidth to the parameter control unit according to the measurement sequence, and receiving the IQ data from the measurement unit, performing spectrum analysis and saving the measurement data.

3. The signal receiving unit (1) according to claim 2, characterized in that... : It includes a directional receiving antenna coil (13), an antenna coil turntable (5), a tuning network (6), and an impedance matching transformer (7). Among them, the parameter adjustable function module consists of an antenna digitally controlled potentiometer and an adjustable capacitor module.

4. Signal measurement unit (2), characterized in that: (1) The function of attenuator (8) is to attenuate large signals so that they are within the linear region of the amplifier. (2) The filter (9) filters the input signal, filtering out noise and interference signals outside the measurement bandwidth. (3) Amplifier (10) is a low-noise linear amplifier, which amplifies small signals to a suitable range for AD sampling. (4) The AD sampler (11) is used to sample and convert analog signals into digital signals according to the sampling rate. For signal matching, the sampling rate is generally set to an integer multiple of the sampling carrier signal. (5) The digital DDC (12) implements digital downsampling and downconversion functions. Internally, it first performs Hilbert transformation on the sampled digital signal to obtain a complex signal, and then downconverts the signal to the baseband frequency or intermediate frequency to obtain I / Q sampling signals.

5. Parameter control unit (3), characterized in that: Based on the center frequency and bandwidth of the signal, the access parameters of the digitally controlled potentiometer, the adjustable capacitor module and the turns ratio of the impedance matching transformer in the tuning network are set to control the rotation speed and angle of the turntable (5), and the appropriate settings of the attenuator (8), filter (9), amplifier (10), AD (11) sampler and digital downconversion synthesizer (DDC) (12) are selected. in, (1) A digital potentiometer is a new type of CMOS digital and analog mixed signal processing integrated circuit. The resistance value is adjusted by numerical control, and the resistor network is designed according to the bandwidth. (2) The programmable capacitor module uses a high-precision capacitor network in conjunction with the switching of multiple relays to achieve capacitor regulation. The capacitor network is designed according to the frequency. (3) Impedance matching transformer (7) The turns ratio is designed based on the antenna output impedance and the load circuit input impedance. The primary side of the transformer has multiple access points, and the turns ratio can be adjusted by switching the access points. (4) The turntable (5) is a CNC turntable. The encoder detects the rotation angle of the turntable spindle and converts it into a digital signal, which is then transmitted to the controller for processing. The rotation angle and speed of the turntable are controlled by the program. (5) The attenuator (8) can be set with attenuation level n. By changing the internal attenuation resistor network, the attenuation can be set in units of n*3dB, where n = 0, 1, ...

10. (6) The filter (9) can be set to high-pass, low-pass, or band-pass filtering. The system hardware has built-in low-pass filter L, high-pass filter M, and band-pass filter N. Users can select the appropriate filter according to the actual situation. The high-pass filter range is [f1,∞], the low-pass filter range is [0,f2], and the band-pass filter range is [f1,f2], where f1 and f2 can be set according to the actual signal. (7) The input of amplifier (10) is the amplification factor. The value of the amplifier can be changed by setting the peripheral circuit. Due to the linear region limitation, it is necessary to calculate that the input signal is within the linear region. This can be achieved by the AGC automatic gain control circuit. (8) The sampling rate of the AD sampler (11) can be flexibly set as AD sampling rate = AD sampling clock frequency / N, where N is the frequency division coefficient. (9) The digital DDC (12) can set the downsampling rate.

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