Image: eLoran transmission site at Wildwood, NJ used for government GPS backup demonstrations and research.

Blog Editor’s Note: Another summary of the problem and some technologies that can contribute to the solution.

We note and appreciate it is published in Asia where China’s big push to get folks using Bei Dou is particularly strong. Very good the author discusses that ALL GNSS are vulnerable.



Satellite navigation jamming is a growing concern in the Asia-Pacific. Fortunately, there are steps nations can take to mitigating this menace.

 by Dr. Thomas Withington

A satellite navigation signal travels along to reach us. The US’ Global Positioning System (GPS) has a constellation of satellites positioned approximately 20,200 kilometres (12,550 miles) above Earth. Their signals have a strength of 54.8 decibels/ milliwatt (dBm) when they leave the spacecraft. When they reach Earth, these signals will have reduced to a strength as low as -130dBm. The lower the dBm number, the weaker the signal. This explains why GPS signals get easily blocked by large buildings in urban areas and by thick tree canopy in a forest or jungle.

Why are these signals so weak? They must travel a long way to reach Earth. Like a marathon competitor, the runner has far more energy at the start of the race than at the end. Signals are also weak as they are generated by a satellite’s solar panels and because the spacecraft are transmitting continuously. Furthermore, space is a finite resource on a satellite. A balance must be struck between the mass of the satellite’s electricity generation equipment and its size and weight so it can be safely and economically launched. The net result is weak GNSS (Global Navigation Satellite System) signals which are easy to jam and spoof.