A system and method for calibrating channel delay of a Loran-C timing terminal

Abstract

The application provides a Loran-C timing terminal channel time delay calibration system and method, which first measures the time delay T0 between a reference Loran-C signal output by a Loran-C timing signal simulator and a reference 1PPS signal, and completes calibration of the simulator; secondly, measures the time delay T1 of a signal transmitting device, and completes calibration of the transmitting device; thirdly, measures the time difference T2 between the reference 1PPS output by the Loran-C timing signal simulator and the 1PPS signal output by the Loran-C timing terminal to be measured; and finally, obtains the channel time delay AT of the Loran-C timing terminal to be measured, AT=T2-T1-T0. The application does not need an additional standard Loran-C timing terminal as a reference, reduces the uncertainty of the time delay measurement in the relative time delay calibration method, and can ensure the accuracy of the time delay measurement of the Loran-C timing terminal.

Description

TECHNICAL FIELD

[0001] The present application relates to a time delay calibration system and method, which can measure and calibrate the absolute channel time delay of various types of Loran-C timing terminals. BACKGROUND

[0002] The Loran-C system is an important supplement and backup of satellite navigation system, and can provide high-precision time service for users. The time service capability of the Loran-C system is mainly completed by various types of Loran-C timing terminals. The Loran-C user timing terminal in China has the largest market space and extensive application demand in the world, and in the system construction aspect, the Loran-C differential receiver will be used to complete the generation of the propagation time delay difference data, and the Loran-C timing monitoring receiver will be used to complete the monitoring of the system state and signal quality; in the user use aspect, the Loran-C user timing receiver will be mainly used to complete the time service. The channel time delay of the Loran-C timing terminal refers to the time used for the Loran-C signal to enter the antenna and then to generate a 1PPS signal after being processed by the terminal. Due to the lack of technical means and calibration system, the current Loran-C factory timing terminal lacks a unified time delay test calibration system, some simple calibration or even no calibration is performed, thereby resulting in a large timing error of the user terminal, the performance cannot be guaranteed, and the system construction and user use precision are seriously affected.

[0003] Loran-C signals are pulse signals with a center frequency of 100kHz and a bandwidth of 20kHz, and their wavelengths reach the three-kilometer range. Calibrating the time delay of Loran-C timing terminals in a laboratory environment has always been a challenge. Currently, there are three methods for calibrating Loran-C timing terminals. Method one uses a relative time delay measurement method, comparing the timing results of a calibrated standard Loran-C timing terminal with the terminal under test by receiving the actual Loran-C signal. While this method is simple, the standard timing terminal's time delay calibration is inaccurate and difficult to calibrate itself. Furthermore, interference in the test environment and unstable propagation paths can lead to decreased accuracy and increased uncertainty in the calibration results. Method two involves a wired connection of the Loran-C timing terminal to a Loran-C timing signal analog source. One method involves sending the signal to the Loran-C timing terminal host for time delay calibration. However, antenna time delay is generally ignored or estimated, resulting in poor accuracy and unsuitability for calibrating the entire system. A third method uses equivalent impedance and antenna couplers to simulate antenna circuitry. The Loran-C timing analog signal is sent to the simulated antenna circuit via a wired connection, processed, and then sent to the Loran-C timing terminal for measurement. This method requires simulating different circuits for different antennas, leading to complex fabrication, high workload, poor circuit matching, and discrepancies between the simulated and actual antennas, further contributing to poor time delay calibration accuracy. In summary, current Loran-C timing terminal channel time delay calibration methods are poor in both accuracy and feasibility, lacking a unified, standardized, and reliable system and method. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a Loran-C timing terminal channel delay calibration system, which can measure and calibrate the channel delay of Loran-C timing terminals. It is applicable to the channel delay calibration of various types of Loran-C timing terminals, such as Loran-C user timing receivers, Loran-C differential receivers, and Loran-C monitoring receivers.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a Loran-C timing terminal channel delay calibration system, including a shielded room, a frequency distribution amplifier, a signal transmitting device, a measuring device, and a calibration device.

[0006] The frequency distribution amplifier amplifies and distributes the external high-stability 10MHz frequency reference into multiple unified 10MHz frequencies, providing an external 10MHz frequency reference for the signal transmitting device, calibration equipment, measurement equipment, and Loran-C timing terminal under test.

[0007] The signal transmitting device includes a Loran-C timing signal simulator, a low-noise power amplifier / distributor, and a Helmholtz coil. The Loran-C timing signal simulator generates a Loran-C timing analog signal according to the standard Loran-C signal format and encoding method. After the low-noise power amplifier / distributor amplifies and distributes the Loran-C timing analog signal to be transmitted, it provides Loran-C signals with the same amplitude and phase to the two Helmholtz coils respectively. The Helmholtz coils are placed in the shielded room, radiating the output signal of the low-noise power amplifier / distributor into space to form a uniform field. The Loran-C receiving antenna is placed in the uniform field and transmits the received spatial signal to the Loran-C timing terminal under test.

[0008] The measuring device includes a time interval counter and a computer. The time interval counter acquires the time difference data between the reference 1PPS signal output by the Loran-C signal simulator and the timing 1PPS signal output by the Loran-C timing receiver under test. The computer completes the acquisition of the time difference data and the calculation of the receiver delay.

[0009] The calibration equipment completes the time delay calibration of the Loran-C timing signal simulator and the signal transmitting device.

[0010] The Loran-C receiving antenna is positioned at the midpoint between the two Helmholtz coils in the horizontal and vertical directions.

[0011] The calibration equipment includes an oscilloscope, a vector network analyzer, and a standard antenna. The oscilloscope measures the time delay between the reference 1PPS signal output by the Loran-C timing signal simulator and the reference Loran-C signal. The vector network analyzer measures the time delay of the signal transmitting device and the cable. The standard antenna has a known time delay and is capable of receiving 100kHz low-frequency continuous wave signals in space, used in conjunction with the vector network analyzer to complete the time delay calibration of the transmitting device.

[0012] This invention also provides a method for Loran-C timing terminal channel delay calibration based on the above system, comprising the following steps:

[0013] Step 1: Obtain the time delay T0 between the starting position of the Loran-C timing signal output from the Loran-C timing signal simulator and the rising edge of the reference 1PPS signal;

[0014] Step 2: Using the 10MHz signal input from the frequency distribution amplifier as a reference, output a 100kHz continuous wave signal; send the 100kHz continuous wave signal into two Helmholtz coils respectively, and the Helmholtz coils radiate the signal into space; use a standard receiving antenna to receive the signal in space, measure the time delay of the signal received by the standard receiving antenna relative to the 100kHz signal, and then obtain the time delay T1 of the transmitting device.

[0015] Step 3: After setting the station signal to be output in the Loran-C timing signal simulator, the reference Loran-C timing signal is amplified and transmitted through a Helmholtz coil. The receiving antenna of the Loran-C timing terminal under test is placed at the midpoint between the horizontal and vertical directions of the two Helmholtz coils. The Loran-C timing terminal under test processes the antenna received signal and generates a timing 1PPS signal. The time difference T2 between the reference 1PPS signal output by the Loran-C timing signal simulator and the timing 1PPS signal output by the Loran-C timing terminal under test is measured. Finally, the channel delay of the Loran-C timing terminal is calculated as ΔT = T2 - T1 - T0.

[0016] Step 1 first uses a frequency distribution amplifier to amplify and distribute the external reference 10MHz signal into multiple 10MHz signals. The output 10MHz frequency is then connected to the Loran-C signal simulator and oscilloscope. The Loran-C signal simulator is set to lead the Loran-C pulse signal by 30μs. The reference 1PPS signal output by the simulator and the output reference Loran-C signal are connected to the oscilloscope using cables of equal length. The reference 1PPS signal is used as the trigger. The time delay T0 of the output reference 1PPS signal relative to the positive zero-crossing point of the first pulse of the output reference Loran-C signal pulse group at 30μs is measured by the oscilloscope.

[0017] Step 2 measures the time delay τ0 of the signal received by the standard receiving antenna relative to the 100kHz signal, where the time delay of the standard receiving antenna is known as τ1, and the time delay of the cable from the standard receiving antenna to the vector network analyzer is measured as τ2, thus obtaining the time delay of the transmitting device T1 = τ0 - (τ1 + τ2).

[0018] The time delay of the cable from the standard receiving antenna to the vector network analyzer is measured using the vector network analyzer.

[0019] Step 3 utilizes a Loran-C timing signal simulator to output a reference 1PPS signal as the door opening signal, and the Loran-C timing terminal under test to output a timing 1PPS signal as the door closing signal, measuring the time difference between the two; within a set time period, N points of time difference data Δτ1, Δτ2...Δτ are obtained. NCalculate the mean T2 of the time difference data sequence at N points: T2 = (Δτ1 + Δτ2 + ... + Δτ N ) / N.

[0020] The beneficial effects of this invention are:

[0021] (1) Based on the calibration of the measurement calibration system, this invention can measure the absolute time delay of the entire Loran-C timing terminal;

[0022] (2) This invention differs from the relative time delay calibration method in that it does not require an additional standard Loran-C timing terminal as a reference, thus reducing the uncertainty of time delay measurement in the relative time delay calibration method;

[0023] (3) The present invention uses a Helmholtz coil to form a uniform far-field signal of Loran-C within a certain range to simulate the actual received signal. The receiving antenna of any type of Loran-C timing terminal can be used.

[0024] (4) This invention is carried out in a shielded room, which can prevent the influence of external Loran-C transmitter signals and interference signals on the accuracy of time delay measurement;

[0025] (5) All measuring devices and Loran-C timing terminals under test in this invention can ensure the accuracy of Loran-C timing terminal delay measurement under a unified high-stability 10MHz frequency reference source;

[0026] (6) The present invention can also measure the anti-interference performance of Loran-C timing terminal by setting a Loran-C timing signal analog source to output Loran-C band interference signal. Attached Figure Description

[0027] Figure 1 This is a basic schematic diagram of the Loran-C timing terminal channel delay calibration.

[0028] Figure 2 This is a schematic diagram of the Loran-C time signal simulator for time delay calibration.

[0029] Figure 3 This is a graph showing the relationship between signal and 1PPS during time delay calibration using the Loran-C time signal simulator.

[0030] Figure 4 This is a graph showing the measured time delay results from the Loran-C time signal simulator;

[0031] Figure 5 This is a schematic diagram of the delay calibration components of a signal transmitting device;

[0032] Figure 6 This is a schematic diagram of the Loran-C timing terminal delay calibration system. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments. The present invention includes, but is not limited to, the following embodiments.

[0034] This invention provides a Loran-C timing terminal channel delay calibration system, including a shielded room, a frequency distribution amplifier, a signal transmitting device, a measuring device, and a calibration device.

[0035] The shielding room is mainly used to shield against external interference and signals transmitted from the external Loran-C station, providing a clean electromagnetic environment for time delay calibration. It is mainly composed of shielding materials.

[0036] The frequency distribution amplifier amplifies and distributes the external high-stability 10MHz frequency reference into multiple unified 10MHz frequencies, providing an external 10MHz frequency reference for the signal transmitting device, calibration equipment, measurement equipment, and Loran-C timing terminal under test in the entire time delay calibration process, ensuring that the entire measurement and calibration process is carried out under a stable and unified clock source.

[0037] The aforementioned signal transmitting device is mainly used for the generation and transmission of low-frequency continuous wave signals and Loran-C signals. The device primarily consists of a Loran-C timing signal simulator, a low-noise power amplifier / distributor, and a Helmholtz coil. The Loran-C timing signal simulator generates Loran-C timing analog signals according to the standard Loran-C signal format and encoding method. The low-noise power amplifier / distributor amplifies and distributes the Loran-C timing analog signals to be transmitted, providing the Helmholtz coil with two Loran-C signals of the same amplitude and phase, ensuring that the signal strength transmitted into space meets the test requirements. The Helmholtz coil radiates the output signal of the low-noise power amplifier / distributor into space, forming a uniform field within a certain range to provide a spatial signal for time delay calibration.

[0038] The aforementioned measuring equipment primarily performs time difference measurement, data acquisition, and calculation, and includes a time interval counter and a computer. The time interval counter measures the time difference between the reference 1PPS signal output by the Loran-C signal simulator and the timing 1PPS signal output by the Loran-C timing receiver under test; the computer acquires the time difference data and calculates the receiver delay.

[0039] The calibration equipment primarily calibrates the time delay of the Loran-C timing signal simulator and the signal transmitting device. The calibration equipment mainly includes an oscilloscope, a vector network analyzer, and a standard antenna. The oscilloscope is mainly used to measure the time delay between the reference 1PPS signal output by the Loran-C timing signal simulator and the reference Loran-C signal; the vector network analyzer measures the time delay of the signal transmitting device and the cable delay; the standard antenna, with a known time delay, is capable of receiving 100kHz low-frequency continuous wave signals in space and is used in conjunction with the vector network analyzer to complete the time delay calibration of the transmitting device.

[0040] This invention also provides a Loran-C timing terminal channel delay calibration method, which is performed on the aforementioned Loran-C timing terminal channel delay calibration system. The channel delay calibration mainly includes the following steps:

[0041] Step 1: Loran-C Timing Signal Simulator Delay Calibration. This mainly refers to the time delay between the starting position of the Loran-C signal output from the Loran-C timing signal simulator and the rising edge of the reference 1PPS signal. First, the external reference 10MHz signal is amplified and distributed into multiple 10MHz signals using a frequency distribution amplifier. The output 10MHz frequencies are then connected to the Loran-C signal simulator and oscilloscope. Since the starting level of the Loran-C signal is low and difficult to measure, a measurement at 30μs is selected. The simulator is set to lead the Loran-C pulse signal by 30μs. The reference 1PPS signal output from the simulator and the Loran-C signal output from the reference are connected to the oscilloscope using cables of equal length. Using the reference 1PPS signal as the trigger, the time delay T0 of the output reference 1PPS signal relative to the positive zero-crossing point 30μs from the first pulse of the output reference Loran-C signal pulse group is measured using the oscilloscope.

[0042] Step 2: Signal Transmitter Delay Calibration. The vector network analyzer uses the 10MHz signal input from the frequency distribution amplifier as a reference and outputs a 100kHz continuous wave signal. The 100kHz continuous wave signal is sent to a low-noise power amplifier distributor to generate two identical 100kHz signals, which are then sent to a Helmholtz coil placed in a shielded room. The Helmholtz coil radiates the signal into space. Finally, a standard receiving antenna is placed at the midpoint between the horizontal and vertical directions of the Helmholtz coil. The standard receiving antenna receives the signal in space and sends it to the vector network analyzer. The vector network analyzer uses its group delay measurement function to measure the delay τ0 of the signal received by the standard receiving antenna relative to the 100kHz signal output by the vector network analyzer. The delay of the standard receiving antenna is known as τ1, and the delay of the cable from the standard receiving antenna to the vector network analyzer can be measured by the vector network analyzer as τ2. Therefore, the delay T1 of the transmitting device can be obtained, where T1 = τ0 - (τ1 + τ2).

[0043] Step 3: Loran-C Timing Terminal Channel Delay Measurement and Calculation. The external reference 10MHz signal is amplified by a frequency distribution amplifier and then fed into the Loran-C timing signal simulator, time interval counter, and the Loran-C timing terminal under test. After setting the required station signal in the Loran-C timing signal simulator (the reference Loran-C signal does not need to be led by 30μs), the reference Loran-C timing signal is output to a low-noise power amplifier / distributor. Finally, the reference Loran-C timing signal is transmitted through a Helmholtz coil in a shielded room. The receiving antenna of the Loran-C timing terminal under test is placed at the midpoint between the horizontal and vertical directions of the Helmholtz coil to receive the reference Loran-C timing signal in the shielded room. The Loran-C timing terminal processes the received signal and generates a 1PPS timing signal. The high-precision time interval counter uses a Loran-C time signal analog source to output a reference 1PPS signal as the gate opening signal, and a Loran-C timing terminal to output a timing 1PPS signal as the gate closing signal. The time difference between the two is measured to obtain time difference data Δτ1, Δτ2...Δτ at N points over a certain period of time. N The time difference sequence is then fed into a computer for processing. The mean of the N-point time difference data sequence, T2, is calculated as: T2 = (Δτ1 + Δτ2 + ... + Δτ N ) / N, and finally the Loran-C timing terminal channel delay is calculated to be ΔT=T2-T1-T0.

[0044] The Loran-C timing terminal channel delay calibration system described in this embodiment of the invention consists of a shielded room, a frequency distribution amplifier, a signal transmitting device, measuring equipment, and calibration equipment. The basic principle of Loran-C timing terminal channel delay calibration is as follows: Figure 1As shown, the main steps are: first, measure the time delay T0 between the Loran-C time synchronization signal simulator output reference Loran-C signal and reference 1PPS signal to complete simulator calibration; second, measure the time delay T1 of the signal transmitting device to complete transmitting device calibration; third, connect the receiver under test to the system and measure the time difference T2 between the Loran-C time synchronization signal simulator output reference 1PPS and the Loran-C timing terminal under test output 1PPS signal. The channel delay ΔT of the Loran-C timing terminal under test can be calculated as ΔT = T2 - T1 - T0. In this embodiment, the external reference 10MHz signal is the national standard time UTC (NTSC) 10MHz frequency signal maintained in national time synchronization. Besides the equipment described in this embodiment, which can be replaced with equivalent functions, other equipment can also be developed according to requirements.

[0045] This embodiment follows Figure 2 The device connections were used to calibrate the Loran-C timing signal analog source. The oscilloscope used was a Tektronix MSO4104B, and the frequency distribution amplifier was a TimeTech 10273. After all devices were working properly, the repetition period of the Loran-C timing signal analog source output signal group was set to 60ms. This ensures that the reference 1PPS signal and the reference Loran-C signal start position will repeat every 3 seconds, facilitating measurement. The Loran-C signal output from the Loran-C timing signal analog source was led by 30μs. The oscilloscope was set to use the simulator output reference 1PPS signal as the trigger, and the oscilloscope's time domain resolution was adjusted to 2ns. The delay between the 30μs zero-crossing point of the pulse signal and the reference 1PPS signal was measured by adjusting the amplitude of the reference Loran-C signal. Figure 3 The diagram shows the positional relationship between the reference 1PPS and the reference Loran-C signal. Figure 4 The oscilloscope shows the calibration results for the analog source. The time delay is 2.8 ns, so the time delay of the reference Loran-C signal relative to the reference 1PPS signal is T0 = 2.8 ns.

[0046] This embodiment follows Figure 5The signal transmitting device was calibrated using the connection relationships between the devices. A Rohdeschwarz ZNB4 vector network analyzer was used, with a Helmholtz coil radius of 2 meters and a distance of 2 meters between the two coils. The vector network analyzer's built-in signal source was configured to transmit a 100kHz frequency signal from port 1 to a low-noise RF amplifier / distributor, which then released the signal into the shielded room via the Helmholtz coil. A standard antenna was placed at the midpoint between the horizontal and vertical positions of the Helmholtz coil. The signal from the shielded room was received by the standard receiving antenna and sent to port 2 of the vector network analyzer. The group delay function of the vector network analyzer measured the delay to be 202953.1 ns. The standard antenna delay was 89049.5 ns, and the cable delay, measured by the vector network analyzer, was 10.8 ns. Therefore, the signal transmitting device delay T1 can be calculated as: T1 = 202953.1 - 89049.5 - 10.8 = 113892.8 ns.

[0047] This embodiment follows Figure 6 The connection relationships of the equipment were used to measure and calibrate the delay of the Loran-C timing terminal under test. The frequency distribution amplifier used was a TimeTech 10273, and the time interval counter used was a Stanford SR620. The Loran-C timing signal analog source was set to output a Loran-C timing signal with a repetition period of 60ms. The receiving antenna of the Loran-C timing terminal under test was placed at the midpoint between the horizontal and vertical positions of the Helmholtz coil in the shielded room to receive the Loran-C signal. After the Loran-C timing terminal was working normally, the time difference between the reference 1PPS signal and the timing 1PPS signal measured by the high-precision time interval counter was collected using a computer for 10 minutes. The average time difference was 178210.4ns, therefore the timing terminal channel delay can be obtained as ΔT=T2-T1-T0=178210.4-113892.8-2.8=64314.8ns.

[0048] The detailed descriptions of the technical solutions of the present invention provided in the embodiments are illustrative and not restrictive. Those skilled in the art can modify the technical solutions described in the embodiments or make equivalent substitutions for some of the technical features based on reading this specification; however, these modifications or substitutions do not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Loran-C timing terminal channel delay calibration system, comprising a shielded room, a frequency distribution amplifier, a signal transmitting device, measuring equipment, and calibration equipment, characterized in that, The frequency distribution amplifier amplifies and distributes an external high-stability 10MHz frequency reference into multiple unified 10MHz frequencies, providing an external 10MHz frequency reference for the signal transmitting device, calibration equipment, measurement equipment, and the Loran-C timing terminal under test. The signal transmitting device includes a Loran-C timing signal simulator, a low-noise power amplifier / distributor, and Helmholtz coils. The Loran-C timing signal simulator generates a Loran-C timing analog signal according to the standard Loran-C signal format and encoding method. After the low-noise power amplifier / distributor amplifies and distributes the Loran-C timing analog signal to be transmitted, it provides amplitude and phase signals to the two Helmholtz coils respectively. The Loran-C signal is transmitted in a uniform field. The Helmholtz coil, housed in the shielded room, radiates the output signal from the low-noise power amplifier / distributor into the space. The Loran-C receiving antenna, placed within this uniform field, transmits the received spatial signal to the Loran-C timing terminal under test. The measuring device includes a time interval counter and a computer. The time interval counter acquires the time difference data between the reference 1PPS signal output by the Loran-C signal simulator and the timing 1PPS signal output by the Loran-C timing receiver under test. The computer performs the acquisition of the time difference data and the calculation of the receiver delay. The calibration device performs time delay calibration on the Loran-C timing signal simulator and the signal transmitting device.

2. The Loran-C timing terminal channel delay calibration system according to claim 1, characterized in that, The Loran-C receiving antenna is positioned at the midpoint between the two Helmholtz coils in the horizontal and vertical directions.

3. The Loran-C timing terminal channel delay calibration system according to claim 1, characterized in that, The calibration equipment includes an oscilloscope, a vector network analyzer, and a standard antenna. The oscilloscope measures the time delay between the reference 1PPS signal output by the Loran-C timing signal simulator and the reference Loran-C signal. The vector network analyzer measures the time delay of the signal transmitting device and the cable. The standard antenna has a known time delay and is capable of receiving 100kHz low-frequency continuous wave signals in space, used in conjunction with the vector network analyzer to complete the time delay calibration of the transmitting device.

4. A method for calibrating the Loran-C timing terminal channel delay using the system described in claim 1, characterized in that, Includes the following steps: Step 1: Obtain the time delay T0 between the starting position of the Loran-C timing signal output from the Loran-C timing signal simulator and the rising edge of the reference 1PPS signal; Step 2: Using the 10MHz signal input from the frequency distribution amplifier as a reference, output a 100kHz continuous wave signal; send the 100kHz continuous wave signal into two Helmholtz coils respectively, and the Helmholtz coils radiate the signal into space; use a standard receiving antenna to receive the signal in space, measure the time delay of the signal received by the standard receiving antenna relative to the 100kHz signal, and then obtain the time delay T1 of the transmitting device. Step 3: After setting the station signal to be output in the Loran-C timing signal simulator, the reference Loran-C timing signal is amplified and transmitted through a Helmholtz coil. The receiving antenna of the Loran-C timing terminal under test is placed at the midpoint between the horizontal and vertical directions of the two Helmholtz coils. The Loran-C timing terminal under test processes the antenna received signal and generates a timing 1PPS signal. The time difference T2 between the reference 1PPS signal output by the Loran-C timing signal simulator and the timing 1PPS signal output by the Loran-C timing terminal under test is measured. Finally, the channel delay of the Loran-C timing terminal is calculated as ΔT = T2 - T1 - T0.

5. The Loran-C timing terminal channel delay calibration method according to claim 4, characterized in that, Step 1 first uses a frequency distribution amplifier to amplify and distribute the external reference 10MHz signal into multiple 10MHz signals. The output 10MHz frequency is then connected to the Loran-C signal simulator and oscilloscope. The Loran-C signal simulator is set to lead the Loran-C pulse signal by 30μs. The reference 1PPS signal output by the simulator and the output reference Loran-C signal are connected to the oscilloscope using cables of equal length. The reference 1PPS signal is used as the trigger. The time delay T0 of the output reference 1PPS signal relative to the positive zero-crossing point of the first pulse of the output reference Loran-C signal pulse group at 30μs is measured by the oscilloscope.

6. The Loran-C timing terminal channel delay calibration method according to claim 4, characterized in that, Step 2 measures the time delay τ0 of the standard receiving antenna signal relative to the 100kHz signal, where the standard receiving antenna time delay is known as τ1, and the time delay of the cable from the standard receiving antenna to the vector network analyzer is measured as τ2, thus obtaining the time delay of the transmitting device T1 = τ0 - (τ1 + τ2).

7. The Loran-C timing terminal channel delay calibration method according to claim 6, characterized in that, The time delay of the cable from the standard receiving antenna to the vector network analyzer is measured using the vector network analyzer.

8. The Loran-C timing terminal channel delay calibration method according to claim 4, characterized in that, Step 3 involves using a Loran-C timing simulator to output a reference 1PPS signal as the door opening signal, and the Loran-C timing terminal under test to output a timing 1PPS signal as the door closing signal, measuring the time difference between the two; and obtaining N points of time difference data Δτ1, Δτ2...Δτ within a set time period. N Calculate the mean T2 of the N-point time difference data sequence: T2 = (Δτ1 + Δτ2 + ... + Δτ N ) / N.

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