Easily Troubleshoot Signal Interference Using the Embedded Spectrum Analysis on BX50 Series Boards
Huayu Zhang, Tersus GNSS      21 Feb, 2025

In the practical application of GNSS receivers, especially in complex outdoor environments, signal interference is one of the common issues that lead to degraded positioning performance. The sources of interference are diverse, mainly including:

◆ Environmental Interference: Includes multipath effects from tall buildings or signal attenuation through dense vegetation.  
◆ Man-made Interference: Electromagnetic interference from nearby electronic devices, radio transmitters, or other wireless equipment. 
◆ Co-channel Interference: Influence from communication signals in adjacent frequency bands (e.g., 4G or 5G) on the GNSS frequency band. 
◆ Occasional Interference: Signal fluctuations caused by temporary signal jamming devices (jammers) or weather changes.

These interferences can reduce the receiver's positioning accuracy and lead to signal loss or even device malfunctions. Therefore, timely detection and effective troubleshooting of interference sources are crucial to ensuring the stable operation of the receiver. By leveraging the embedded spectrum analysis function of the BX50 series boards, troubleshooting efficiency can be significantly improved, providing precise evidence for problem resolution.

Background
On December 1, 2024, during an on-site inspection in Shenzhen, a significant position drift anomaly was found in the data obtained from the static observation of a GNSS receiver, which integrates the Tersus BX50M-TAP board.

Given the testing environment was primarily open, it was suspected that the issue might be related to signal interference. By analyzing the provided raw data, significant interference was found in the L2 and L5 frequency bands. However, as the client was using their own antenna with the BX50 series board, the source of the interference was unclear, and further investigation was needed to confirm whether the interference originated from the antenna, the environment, or the receiver equipment itself.


Objective
The objective is to leverage the embedded spectrum analysis function of the BX50 series boards, along with the visual display of Tersus GNSS Center software, to identify the source of positioning signal interference, troubleshoot and resolve the issue, ensuring the accuracy and stability of the receiver's positioning data. The blue shaded area represents the measurement error of two satellite signals, while the gray shaded area represents the uncertain region of the receiver's position.

Guide to Enabling Spectrum Analysis Functions

Step 1: Connect the BX50 series boards to the computer and open the RF Spec Interval window in Tersus GNSS Center.

Step 2: Input Command - Enable Anti-Interference spectrum analysis Function:
-> rfspectrumcontrol enable
-> saveconfig
-> Reset

Step 3: Input Command - Set Sampling Interval to Output at a Specific Frequency:
-> log rfspectrumb ontime 0.1

  Significance of the Function: 

  ◆ It collects and analyzes signal spectrum data, including interference detection and signal strength variations, etc., helping to identify environmental changes or signal interference. 
  ◆ It can be used to detect sudden interference or periodic signal anomalies, such as frequency-hopping interference or strong signal shielding, defining interval periods for evaluating RF performance. 
  ◆ Users can adjust the analysis or sampling interval by setting parameters, allowing it to provide sampling functions similar to those of a spectrum analyzer. 
 

Main Process
1. Antenna Impact on Signal Troubleshooting
    1) Deploy the BX50M-TAP board and AX4E02 antenna on-site.  Analyze the on-site environment, the number of observable satellites, L-Band satellite signal-to-noise ratio, and other basic testing conditions to ensure they meet the requirements. Control variables by ensuring consistent firmware, parameter settings, stable power supply, and proper cable connections.
    2) After powering on, perform a comparison test with the target device.

    3) Start the Tersus GNSS Center software, connect the test equipment, and enable the spectrum analysis function.
    4) Observe signals in different frequency bands and record spectrum characteristics and interference features.
    5) Compare the test results using the proprietary antenna and the target device’s antenna, analyzing the impact of different antennas on frequency band signals.
    6) Gradually troubleshoot and confirm that the antenna’s interference on the signal is not significant.

2. Interference Source Localization Analysis
    1) Verify the suspected interference sources, such as suspecting the target receiver device to be the source of interference. Connect the BX50M-TAP board to the AX4E02 antenna, then vary the distance between the antenna and the target device to observe interference intensity changes.

2) Record the spectrum data of the receiver and target device at different distances, focusing on the interference signal trends in the L2 and L5 frequency bands.
3) During the testing process, as the distance between the antenna and the target device was increased, it was observed that the interference signals in the spectrum significantly weakened with the increasing distance. 
4) Based on the test results, it was confirmed that the interference source originated from within the target device. 


Troubleshooting and Test Environment Optimization
1. Device Connection Failure: Check the device connection status, reconfigure the communication port and baud rate, and ensure that Tersus GNSS Center can access the receiver data normally.  

2. No Abnormal Frequency Band Signals: If no interference signals are detected, try changing the antenna direction or testing location and expand the troubleshooting scope.  

3. Ensure a Simplified Testing Environment: Minimize interference from external complex signals to avoid affecting the troubleshooting results.


Result
By using the spectrum analysis function of the BX50 series boards, along with the visualization tools in Tersus GNSS Center software, the interference source was successfully located and confirmed to originate from within the target receiver device. During the testing process, real-time signal changes were observed through the spectrum plot. By adjusting the antenna position and distance, it was found that interference signal strength exhibited an inverse correlation with proximity to the target device, further validating the specific location of the interference source

Finally, after eliminating the interference source, the positioning performance significantly improved, and the data became stable and reliable. This analysis provided clear direction for optimizing the target device, while also demonstrating the powerful capability of the BX50 series boards in solving positioning issues in complex interference environments.

About Tersus GNSS Inc.

Tersus GNSS is a leading Global Navigation Satellite System (GNSS) solution provider. Our offerings and services aim to make centimeter-precision positioning affordable for large-scale deployment.

Founded in 2014, we have been pioneers in design and development GNSS RTK products to better cater to the industry’s needs. Our portfolios cover GNSS RTK & PPK OEM boards, David GNSS Receiver, Oscar GNSS Receiver, MatrixRTK [GNSS CORS Systems] and inertial navigation systems.

Designed for ease of use, our solutions support multi-GNSS and provide flexible interfaces for a variety of applications, such as UAVs, surveying, mapping, precision agriculture, lane-level navigation, construction engineering, and deformation monitoring.

Sales inquiry: sales@tersus-gnss.com

Technical support: support@tersus-gnss.com