Global Navigation Satellite System (GNSS) real-time network operators and their customers can have productivity disrupted by interference from errant radio frequency (RF) signals near reference stations that can disrupt low-power GNSS signals. But, for real-time network operators using the Trimble Alloy™ GNSS reference receiver, powered by Trimble’s Maxwell™ 7 GNSS dual chipsets, they are able to collect data with more confidence. With this added ability to monitor and analyze the signals received in each of the GNSS frequency bands, the onboard spectrum analyzer feature helps users identify interference so they can take steps to remove unwanted signals.

A useful tool when an older GNSS reference receiver is not performing well and the cause is unknown, Alloy’s spectrum analyzer can troubleshoot the issue as well as provide data that will help determine a better location for the GNSS reference receiver.

Cause and Mitigation 

Several sources can cause signal interference including:

  • Integration issues: GNSS users generally integrate receivers with other equipment such as an antenna, display, sensors, communications and motors. These pieces can generate some level of RF interference, which can be amplified by the cables used to connect the equipment.
  • Faulty equipment: Over time, components within receivers can become damaged and the level of interference may rise above the approved level. If the frequency generated is at any of the GNSS frequencies or a harmonic, then the close proximity will impact the receiver’s ability to track the true GNSS signals.
  • Legal transmissions in GNSS bands: The frequencies transmitted by GNSS satellites have been allocated and agreed upon by international standards. However, there are many frequencies close to the bands that are approved for other uses (e.g., U.S. amateur television, which has a band that overlaps with GLONASS L2 and Galileo E6) and they can disrupt GNSS tracking.
  • Malicious interference: As GNSS has become a more valuable resource for many activities today, it has also come to the attention of bad actors that profit from disrupting its operation.

To more easily identify potential interference, the spectrum analyzer is embedded in the web user interface (UI) of Trimble’s precision Alloy GNSS reference receiver, replicating many of the traditional features found in benchtop analyzers. However, unlike a traditional analyzer, users can view the spectrum as seen by the receiver. From poorly shielded processor bands to cable assemblies that can radiate enough energy into the antenna to result in significant GNSS band jamming, the spectrum analyzer can report on these and other interferences by sampling a small portion of the digital measurements while the receiver maintains normal operation.

In addition to working simultaneously alongside the receiver’s operation, the spectrum analyzer also:

  • Monitors all GNSS and MSS bands
  • Runs continuously in the background
  • Provides a playback of previous days’ data in waterfall or filtered format
  • Displays real-time data in waterfall, filtered, peak hold or unfiltered formats
  • Has no effect on current receiver functions such as position output, corrections generation or observables streaming

Placing Interference on the Sidelines

One example where the spectrum analyzer helped identify interference from an external source is shown here, where local airport transmitters impacted L-band tracking, represented by the spikes in the plot line.

Another example is onboard interference. In this instance, a vehicle navigation system with poor positioning performance led to a closer look at signal tracking and the spectrum analyzer. The multitude of processors, sensors and cabling integrated on the same platform caused interference when all pieces of the system were in place and powered up. While typically quite difficult to source the interference, the onboard spectrum analyzer significantly sped up the task.

As the wireless spectrum gets increasingly crowded and autonomous systems add more sensors, the amount of interference in GNSS bands will continue to increase. 

The spectrum analyzer feature of Maxwell 7 technology is a critical component in the toolbox of developers releasing products to market within specification and on schedule. For more technical details about this feature, read our white paper on the topic here and watch our webinar here


About the Author

Trimble-Allow-GNSS-Reference-Receiver
Trimble Real-Time Networks

The Trimble Real-Time Networks (RTN) business area supports geospatial applications and industries all over the world, providing reliable hardware and software that integrate seamlessly into an RTN solution for exceptional real-time performance. For more information, visit www.trimble.com/rtn.