Ultra-short wave signal reconnaissance, direction finding and positioning system and method based on unmanned aerial vehicle

Abstract

The invention discloses an ultra-short wave signal reconnaissance and direction finding positioning system and method based on an unmanned aerial vehicle in the technical field of radio signal reconnaissance and direction finding. The system comprises an unmanned aerial vehicle platform, a broadband direction-finding antenna array, a reconnaissance direction-finding load and a ground remote control terminal, wherein the broadband direction-finding antenna array and the reconnaissance direction-finding load are both arranged on the unmanned aerial vehicle platform; the broadband direction-finding antenna array comprises two independent broadband omnidirectional receiving antennas and outputs received signals to the reconnaissance direction-finding load; the reconnaissance direction-finding load comprises an acquisition preprocessing unit and a signal processing unit; the output end of the broadband direction-finding antenna array is connected with the acquisition preprocessing unit, and the acquisition preprocessing unit sends a preprocessing result to the signal processing unit; the ground remote control terminal comprises a load display control module and a flight control module; the load display control module is responsible for issuing a task instruction and receiving reconnaissance information uploaded by the reconnaissance direction-finding load at the same time. The method has the advantages of light weight, low power consumption and no need of regular calibration.

Description

Technical Field

[0001] The present invention relates to the technical field of radio signal reconnaissance and direction finding, and in particular to an ultra-short wave signal reconnaissance, direction finding and positioning system and method based on an unmanned aerial vehicle. Background Art

[0002] Radio signal reconnaissance and direction finding is a passive signal reconnaissance method. It receives and processes the same radio transmission signal in different ways, and then analyzes the signal characteristics from different angles of the same target signal to obtain the azimuth information of the target.

[0003] Conventional direction finding methods are generally amplitude comparison direction finding and phase comparison direction finding, taking portable ultra-short wave signal reconnaissance and direction finding equipment as an example; amplitude comparison direction finding is mainly based on Watson-Watt direction finding. Although Watson-Watt direction finding only requires single channel or dual channel processing for miniaturization and integrated design, it has very strict requirements on amplitude and phase consistency; phase comparison direction finding is mainly based on correlation interferometer. The number of elements in the correlation interferometer has a direct impact on the direction finding accuracy. In terms of balancing direction finding accuracy and portability, correlation interferometers are mostly based on five-element antenna arrays for direction finding;

[0004] However, due to the long wavelength of the ultra-short wave band, the large size of the antenna array is not conducive to the loading of small UAV platforms and is not conducive to the take-off and landing of UAVs; the correlation interferometer direction finding is carried out through correlation calculations with the relevant library, so the relevant library needs to be calibrated regularly and each calibration takes a long time. Summary of the invention

[0005] The purpose of the present invention is to provide a lightweight, low-power consumption UAV-based ultra-short wave signal reconnaissance, direction-finding and positioning system and method, which does not require regular calibration.

[0006] In order to achieve the above-mentioned purpose of the invention, the ultrashort wave signal reconnaissance direction finding and positioning system and method based on unmanned aerial vehicle of the present invention adopts the following technical solutions:

[0007] An ultra-short wave signal reconnaissance direction-finding and positioning system based on a UAV comprises a UAV platform, a broadband direction-finding antenna array, a reconnaissance direction-finding payload and a ground remote control terminal, wherein the broadband direction-finding antenna array and the reconnaissance direction-finding payload are both arranged on the UAV platform;

[0008] The UAV platform is used to receive control instructions and mission instructions issued by the ground remote control terminal, and forward the control instructions, mission instructions, and real-time flight data to the reconnaissance and direction finding payload, and at the same time transmit the reconnaissance information of the reconnaissance and direction finding payload back to the ground remote control terminal;

[0009] The broadband direction-finding antenna array includes two independent wide-band omnidirectional receiving antennas. The broadband direction-finding antenna array outputs the received ultra-short wave signals to the reconnaissance direction-finding payload.

[0010] The reconnaissance and direction-finding payload includes a collection preprocessing unit and a signal processing unit; the output end of the broadband direction-finding antenna array is connected to the collection preprocessing unit, and the collection preprocessing unit sends the preprocessing result to the signal processing unit;

[0011] The ground remote control terminal includes a payload display and control module and a flight control module; the payload display and control module is responsible for issuing mission instructions, while receiving reconnaissance information uploaded by the reconnaissance and direction-finding payload, and then performing a visual display; the flight control module is responsible for issuing control instructions to the UAV platform.

[0012] Preferably, the acquisition preprocessing unit in the reconnaissance and direction finding payload includes two identical radio frequency links.

[0013] Preferably, the flight data includes position information, orientation information, altitude information and attitude information.

[0014] Preferably, the signal processing unit includes a digital down-conversion module, a digitally controlled oscillator, a digital mixer, a digital low-pass filter, a direction finding data calculation module and a direction finding solution module.

[0015] A method for reconnaissance, direction finding and positioning of ultrashort wave signals based on unmanned aerial vehicles, the method comprising the following steps:

[0016] (1) Determine the mission and carry the reconnaissance and direction-finding system to the combat area;

[0017] (2) Setting working parameters;

[0018] (3) Reconnaissance UAV takeoff and equipment status self-check;

[0019] (4) Control the UAV platform to fly to the monitoring location and start reconnaissance and direction finding;

[0020] (5) intercepting signals through a broadband direction-finding antenna array. If the intercepted signal is of an unknown signal type or a known signal type but an unknown frequency signal, an alarm is issued and intercepted signal information is given; if the intercepted signal is of a known signal type and a known frequency, the intercepted signal information is directly output;

[0021] (6) After completing the signal interception mission, the UAV platform rotates in situ around its own center, and two wide-band omnidirectional receiving antennas receive ultra-short wave signals at different times, and then send the received ultra-short wave signals to the acquisition pre-processing unit;

[0022] (7) The acquisition preprocessing unit processes the radio frequency signal and then samples to obtain the digital signal;

[0023] (8) Sending the acquired digital signal to the signal processing unit, performing digital down-conversion and down-speed processing through the digital down-conversion module in the signal processing unit, and then extracting and filtering through the digital controlled oscillator, digital mixer and digital low-pass filter to output IQ signal data;

[0024] (9) The direction finding data calculation module receives the IQ data of the two channels and then calculates the power spectrum and phase spectrum of the two channels respectively;

[0025] (10) The direction finding solution module extracts the power spectrum and the phase spectrum, and calculates the initial azimuth value and the initial elevation angle value of the target signal based on the power spectrum and the phase spectrum;

[0026] The result of the initial value of the azimuth angle is The result of the initial value of the pitch angle is In the formula, is the estimated value of the initial value of the azimuth; is the estimated value of the initial pitch angle; x ab is the initial value of the fuzzy phase difference;

[0027] (11) When the phase obtained by the phase detector is ambiguous, the phase difference between the two channels is rewritten as: In the formula, is the single baseline phase difference obtained by the phase detector; k is the fuzzy number; is random phase noise, and M direction finding baselines are obtained during the UAV's rotation. The following equations are established for each baseline: In the formula, t i represents different sampling moments; k i is a fuzzy number; is the random phase noise, and then k is obtained by calculating each set of equations. i , when the search target angle is close to the true target angle, k i is closest to an integer, in which case the direction finding result is output and the direction finding information is displayed;

[0028] (12) The user selects whether to locate the target or not. If the user does not select the target, the user selects whether to end the work. If the user selects the target, the user arrives at the next monitoring location and starts a new round of direction finding.

[0029] (13) If the work is completed, the reconnaissance and direction finding results are reported to the superior command center. At the same time, if target positioning is selected, go to step (15), otherwise go to step (16);

[0030] (14) If the work is not completed, continue to carry out a new round of reconnaissance and direction finding missions and arrive at the next monitoring location to start direction finding;

[0031] (15) Perform cross-location calculation on the reconnaissance and direction-finding results to obtain target signal location information;

[0032] (16) The mission is completed and the drone returns.

[0033] Preferably, the solution steps of the cross-positioning solution method in step (15) are as follows:

[0034] a) The target position is: P u =r k +d k , where r k is the position of the UAV platform, d k is the distance vector between the UAV platform and the target;

[0035] b) The distance vector formed for each reconnaissance direction finding result is: In the formula, θ k is the azimuth angle at the kth measurement; is the pitch angle at the kth measurement;

[0036] c) Due to the target position, the distance vector d k Cannot be obtained, need to pass with d k Orthogonal unit vectors Multiply to eliminate d k , in P u =r k +d k Multiply both ends simultaneously

[0037] d) After considering the influence of noise, the target position information is measured at N positions and calculated as follows: Among them, a T d k =0,P u is the target position, r is the platform position information, n is the noise term, simplified as AP u =b+n;

[0038] e) Solve the target location information

[0039] Preferably, the RF signal processing in step (7) is to achieve limiting, filtering and amplification of two ultra-short wave signals through two RF links; and the sampling in step (7) is direct sampling through A / D RF.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The reconnaissance and direction-finding device has a simple structure, a small size, and low power consumption, and is easy to carry and quickly deploy. Moreover, compared with the prior art, there is no need to perform direction-finding by performing correlation calculations with a correlation library, so there is no need to perform regular calibration of the correlation library, and the present invention is more convenient to use.

[0042] (2) Cooperating with UAV platforms for aerial reconnaissance, the reconnaissance range is increased while reducing interference signals from the surrounding areas, reducing path loss, reducing multipath effects caused by the ground, and improving direction finding and positioning accuracy;

[0043] (3) Based on the analysis of the reconnaissance target and mission environment, the number of direction finding rotations can be freely selected to achieve higher precision direction finding. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The block diagram of the present invention;

[0045] Figure 2 It is a structural schematic diagram of the present invention;

[0046] Figure 3 It is a work flow chart of the present invention;

[0047] Figure 4 It is the direction finding flow chart of the present invention.

[0048] Among them, there are 1 wide-band omnidirectional receiving antenna, 2 UAV platform, 3 reconnaissance and direction-finding payload, and 4 ground remote control terminal. DETAILED DESCRIPTION

[0049] The present invention is further explained below in conjunction with specific implementation methods. It should be understood that these implementation methods are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0050] like Figure 1-4 As shown, an ultra-short wave signal reconnaissance, direction finding and positioning system based on a UAV includes a UAV platform, a broadband direction finding antenna array, a reconnaissance and direction finding payload and a ground remote control terminal, wherein the broadband direction finding antenna array and the reconnaissance and direction finding payload are both arranged on the UAV platform;

[0051] The UAV platform is used to receive control instructions and mission instructions issued by the ground remote control terminal, and forward the control instructions, mission instructions, and real-time flight data to the reconnaissance and direction finding payload, and at the same time transmit the reconnaissance information of the reconnaissance and direction finding payload back to the ground remote control terminal; among which, the flight data includes position information, azimuth information, altitude information and attitude information;

[0052] The broadband direction-finding antenna array includes two independent wide-band omnidirectional receiving antennas. The broadband direction-finding antenna array outputs the received ultra-short wave signals to the reconnaissance direction-finding payload.

[0053] The reconnaissance and direction-finding payload includes an acquisition preprocessing unit and a signal processing unit; the acquisition preprocessing unit includes two identical 30MHz-3GHz RF channels and an AD RF sampling chip. The RF sampling chip uses ADRV9009, which can filter, amplify, and perform A / D sampling to convert the RF signal sent by the broadband direction-finding antenna array into a digital signal;

[0054] The output end of the broadband direction-finding antenna array is connected to the acquisition preprocessing unit, which sends the preprocessing results to the signal processing unit. The signal processing unit includes a digital down-conversion module, a digitally controlled oscillator, a digital mixer, a digital low-pass filter, a direction-finding data calculation module and a direction-finding solution module, so as to perform further signal analysis and direction-finding solution. The signal processing unit includes an UltraScale series FPGA chip of Xilinx and its supporting peripheral circuits and power supply circuits such as LDO. The PL end of the FPGA chip completes the fast Fourier transform and other signal preprocessing of the digital signal, and the PS end completes the subsequent further signal sorting and processing. At the same time, the PS end is responsible for reading the calculation of the relevant information sent by the drone and the management and upload of the entire payload data.

[0055] The ground remote control terminal includes a payload display and control module and a flight control module; the payload display and control module is responsible for issuing mission instructions, while receiving reconnaissance information uploaded by the reconnaissance and direction-finding payload, and then performing a visual display; the flight control module is responsible for issuing control instructions to the UAV platform.

[0056] The specific working process and principle of the present invention are as follows: after the UAV platform takes off and arrives at the designated location, the UAV platform hovers and completes one to two rotations. The broadband direction-finding antenna array receives the ultrashort wave frequency signal in real time, and then sends the electromagnetic spectrum information during the rotation process to the signal preprocessing unit for filtering, amplification and sampling, and then enters the signal processing unit for signal processing. After calculation combined with the information of the UAV platform itself, it is sent to the ground remote control terminal through the image and data transmission module on the UAV for display and marking.

[0057] A method for reconnaissance, direction finding and positioning of ultrashort wave signals based on unmanned aerial vehicles, the method comprising the following steps:

[0058] (1) Determine the mission and carry the reconnaissance and direction-finding system to the combat area;

[0059] (2) Setting operating parameters, including flight parameters, reconnaissance frequency band, signal type, and known frequencies;

[0060] (3) The UAV platform takes off and performs a self-check on the ultra-short wave reconnaissance and direction-finding payload;

[0061] (4) Control the UAV platform to fly to the monitoring location and start direction finding and reconnaissance;

[0062] (5) intercepting signals through a broadband direction-finding antenna array. If the intercepted signal is of an unknown signal type or a known signal type but an unknown frequency signal, an alarm is issued and intercepted signal information is given; if the intercepted signal is of a known signal type and a known frequency, the intercepted signal information is directly output;

[0063] (6) After completing the signal interception mission, the UAV platform rotates in situ around its own center, and two wide-band omnidirectional receiving antennas receive ultra-short wave signals at different times, and then send the received ultra-short wave signals to the acquisition pre-processing unit;

[0064] (7) The acquisition preprocessing unit performs RF signal processing, realizes limiting, filtering and amplification of two ultra-short wave signals through two RF links, and then performs A / D RF direct sampling to convert the ultra-short wave signals into digital signals;

[0065] (8) Sending the acquired digital signal to the signal processing unit, performing digital down-conversion and down-speed processing through the digital down-conversion module in the signal processing unit, and then extracting and filtering through the digital controlled oscillator, digital mixer and digital low-pass filter to output IQ signal data;

[0066] (9) The direction finding data calculation module receives the IQ data of the two channels, and then calculates the power spectrum and phase spectrum of the two channels respectively, providing raw data for subsequent solution;

[0067] (10) The direction finding solution module extracts the power spectrum and phase spectrum, and based on the power spectrum and phase spectrum, combines the rotation angle of the UAV platform, the baseline length of the broadband direction finding antenna array and other data to calculate the initial azimuth and pitch angle of the target signal;

[0068] The result of the initial value of the azimuth is The result of the initial value of the pitch angle is In the formula, is the estimated value of the initial value of the azimuth; is the estimated value of the initial pitch angle; x ab is the initial value of the fuzzy phase difference;

[0069] (11) When the phase obtained by the phase detector is ambiguous, the phase difference between the two channels is rewritten as: In the formula, is the single baseline phase difference obtained by the phase detector; k is the fuzzy number; is random phase noise, and M direction finding baselines are obtained during the UAV's rotation. The following equations are established for each baseline: Where, t i represents different sampling moments; k i is a fuzzy number; is the random phase noise, and then k is obtained by calculating each set of equations. i , when the search target angle is close to the true target angle, k i is closest to an integer, in which case the direction finding result is output and the direction finding information is displayed;

[0070] (12) The user selects whether to locate the target or not. If the user does not select the target, the user selects whether to end the work. If the user selects the target, the user arrives at the next monitoring location and starts a new round of direction finding.

[0071] (13) If the work is completed, the reconnaissance and direction finding results are reported to the superior command center. At the same time, if target positioning is selected, go to step (15), otherwise go to step (16);

[0072] (14) If the work is not completed, continue to carry out a new round of reconnaissance and direction finding missions and arrive at the next monitoring location to start direction finding;

[0073] (15) Perform cross-positioning solution on the n reconnaissance and direction-finding results to obtain the target signal position information; wherein the solution steps of the cross-positioning solution method are as follows:

[0074] a) The target position is: P u =r k +d k , where r k is the position of the UAV platform, d k is the distance vector between the UAV platform and the target;

[0075] b) The distance vector formed for each reconnaissance direction finding result is: In the formula, θ k is the azimuth angle at the kth measurement; is the pitch angle at the kth measurement;

[0076] c) Due to the target position, the distance vector d k Cannot be obtained, need to pass with d k Orthogonal unit vectors Multiply to eliminate d k , in P u =r k +d k Multiply both ends simultaneously

[0077] d) After considering the influence of noise, the target position information is measured at N positions and calculated as follows: Among them, a T d k =0,P u is the target position, r is the platform position information, n is the noise term, simplified as AP u =b+n;

[0078] e) Solve the target location information

[0079] (16) The mission is completed and the drone returns.

[0080] In the description of the present invention, it is necessary to understand that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "front", "center", "both ends" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0081] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0082] The above description shows and describes the preferred embodiments of the present invention. As mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. An ultra-short wave signal reconnaissance, direction finding and positioning system based on unmanned aerial vehicles, characterized in that: It includes an unmanned aerial vehicle platform, a broadband direction-finding antenna array, a reconnaissance direction-finding payload and a ground remote control terminal, wherein the broadband direction-finding antenna array and the reconnaissance direction-finding payload are both arranged on the unmanned aerial vehicle platform; The UAV platform is used to receive control instructions and mission instructions issued by the ground remote control terminal, and forward the control instructions, mission instructions, and real-time flight data to the reconnaissance and direction finding payload, and at the same time transmit the reconnaissance information of the reconnaissance and direction finding payload back to the ground remote control terminal; The broadband direction-finding antenna array includes two independent wide-band omnidirectional receiving antennas. The broadband direction-finding antenna array outputs the received ultra-short wave signals to the reconnaissance direction-finding payload. The reconnaissance and direction-finding payload includes an acquisition preprocessing unit and a signal processing unit; The output end of the broadband direction finding antenna array is connected to the acquisition preprocessing unit, and the acquisition preprocessing unit sends the preprocessing result to the signal processing unit; The ground remote control terminal includes a payload display and control module and a flight control module; the payload display and control module is responsible for issuing mission instructions, while receiving reconnaissance information uploaded by the reconnaissance and direction-finding payload, and then performing a visual display; the flight control module is responsible for issuing control instructions to the UAV platform.

2. The UAV-based ultrashort wave signal reconnaissance, direction finding and positioning system according to claim 1 is characterized in that: The acquisition preprocessing unit in the reconnaissance and direction finding payload includes two identical radio frequency links.

3. The UAV-based ultrashort wave signal reconnaissance, direction finding and positioning system according to claim 1 is characterized in that: The flight data includes position information, orientation information, altitude information and attitude information.

4. The UAV-based ultrashort wave signal reconnaissance, direction finding and positioning system according to claim 1 is characterized in that: The signal processing unit comprises a digital down-conversion module, a digitally controlled oscillator, a digital mixer, a digital low-pass filter, a direction finding data calculation module and a direction finding solution module.

5. A method for reconnaissance, direction finding and positioning of ultra-short wave signals based on unmanned aerial vehicles, characterized in that: The method comprises the following steps: (1) Determine the mission and carry the reconnaissance and direction-finding system to the combat area; (2) Setting working parameters; (3) Reconnaissance UAV takeoff and equipment status self-check; (4) Control the UAV platform to fly to the monitoring location and start reconnaissance and direction finding; (5) intercepting signals through a broadband direction-finding antenna array. If the intercepted signal is of an unknown signal type or a known signal type but an unknown frequency signal, an alarm is issued and intercepted signal information is given; if the intercepted signal is of a known signal type and a known frequency, the intercepted signal information is directly output; (6) After completing the signal interception mission, the UAV platform rotates in situ around its own center, and two wide-band omnidirectional receiving antennas receive ultra-short wave signals at different times, and then send the received ultra-short wave signals to the acquisition pre-processing unit; (7) The acquisition preprocessing unit processes the radio frequency signal and then samples to obtain the digital signal; (8) Sending the acquired digital signal to the signal processing unit, performing digital down-conversion and down-speed processing through the digital down-conversion module in the signal processing unit, and then extracting and filtering through the digital controlled oscillator, digital mixer and digital low-pass filter to output IQ signal data; (9) The direction finding data calculation module receives the IQ data of the two channels and then calculates the power spectrum and phase spectrum of the two channels respectively; (10) The direction finding solution module extracts the power spectrum and the phase spectrum, and calculates the initial azimuth value and the initial elevation angle value of the target signal based on the power spectrum and the phase spectrum; The result of the initial value of the azimuth angle is The result of the initial value of the pitch angle is In the formula, is the estimated value of the initial value of the azimuth; is the estimated value of the initial pitch angle; x ab is the initial value of the fuzzy phase difference; (11) When the phase obtained by the phase detector is ambiguous, the phase difference between the two channels is rewritten as: In the formula, is the single baseline phase difference obtained by the phase detector; k is the fuzzy number; is random phase noise, and M direction finding baselines are obtained during the UAV's rotation. The following equations are established for each baseline: In the formula, t i represents different sampling moments; k i is a fuzzy number; is the random phase noise, and then k is obtained by calculating each set of equations. i , when the search target angle is close to the true target angle, k i is closest to an integer, in which case the direction finding result is output and the direction finding information is displayed; (12) The user selects whether to locate the target or not. If the user does not select the target, the user selects whether to end the work. If the user selects the target, the user arrives at the next monitoring location and starts a new round of direction finding. (13) If the work is completed, the reconnaissance and direction finding results are reported to the superior command center. At the same time, if target positioning is selected, go to step (15), otherwise go to step (16); (14) If the work is not completed, continue to carry out a new round of reconnaissance and direction finding missions and arrive at the next monitoring location to start direction finding; (15) Perform cross-location calculation on the reconnaissance and direction-finding results to obtain target signal location information; (16) The mission is completed and the drone returns.

6. The method for reconnaissance, direction finding and positioning of ultrashort wave signals based on unmanned aerial vehicles according to claim 5 is characterized in that: The solution steps of the cross-positioning solution method in step (15) are as follows: a) The target position is: P u =r k +d k , where r k is the position of the UAV platform, d k is the distance vector between the UAV platform and the target; b) The distance vector formed for each reconnaissance direction finding result is: In the formula, θ k is the azimuth angle at the kth measurement; is the pitch angle at the kth measurement; c) Due to the target position, the distance vector d k Cannot be obtained, need to pass with d k Orthogonal unit vectors Multiply to eliminate d k , in P u =r k +d k Multiply both ends simultaneously d) After considering the influence of noise, the target position information is measured at N positions and calculated as follows: Among them, a T d k =0,P u is the target position, r is the platform position information, n is the noise term, simplified as AP u =b+n; e) Solve the target location information 7. The method for reconnaissance, direction finding and positioning of ultrashort wave signals based on unmanned aerial vehicles according to claim 5 is characterized in that: The RF signal processing in step (7) is to achieve the limiting, filtering and amplification of two ultra-short wave signals through two RF links; the sampling in step (7) is to directly sample through A / D RF.

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