The Incredible Disappearing Car: Combating GPS Jammers

There will always be a segment of the population that wants to “fly under the radar” and attempt to defeat GPS tracking devices with GPS jammers.

Geotab is dedicated to maintaining a robust and stable system and will continue to make its GO devices as tamper-proof as possible.

By using a GPS jammer, a person in a vehicle being tracked will try to hide his position in an effort to remain undetected. The jammer may be set to operate continuously or could be turned on and off so that a particular portion of a trip is not tracked.

Where in the World Am I? How a GPS System Works

To understand how a jammer functions, we must first understand how the global positioning system (GPS) works. A GPS tracker receives microwave signals from an array of satellite transmitters orbiting the Earth at an altitude of approximately 20,200 km. Once the tracker receives signals from four or more satellites, it determines its position through a series of time calculations and trilateration.

The receiver relies on these precise and specific satellite signals to determine where it is in the world. The GPS tracking device then transmits this position and velocity information to a monitoring location. Usually, this data is communicated over the cellular network.

GPS satellite broadcasting signals
Figure 1: GPS satellite broadcasting signals.

In some cases, satellite malfunction or solar flares can temporarily disrupt the transmission of GPS signals. A GPS jammer sends out a radio signals or signal noise with the same frequency as the GPS device, to override or distort the GPS satellite signals. The GPS device can then no longer calculate its position because the satellite signal is masked by the interference.

What is a GPS Jamming Device?

A GPS jamming device or GPS jammer is typically a small, self-contained, transmitter that generates a 1575.42 Mhz interference signal over a 5 to 10 meter radius.

Typically, the user plugs the jammer into a cigarette lighter and places the unit close enough to a GPS tracker to disrupt the GPS satellite signal. Once powered up, they become fully operational in less than 20 seconds. The relatively low power and quick start up time allow the jammers to be used only when required. Criminals will switch them off as soon as possible to avoid detection. These jammers can be purchased cheaply on the Internet for less than $100.

How Geotab Detects and Eliminates GPS Jamming Threats

Fortunately, the negative effects and usefulness of jammers are minimized with Geotab devices.

MyGeotab picks up GPS signal disruption. When a GPS signal is not received, the Trip History map will show a missing or interrupted trip — clearly calling attention to an issue.

If GPS jamming occurs mid-trip, a straight line will be displayed from when jamming starts to the point where the jamming device is turned off. Anyone monitoring the vehicle will quickly see this and can investigate the cause of the missing trip information.

GPS jamming mygeotab
Figure 2: A straight line in MyGeotab indicates GPS disruption.

More immediate jammer detection is also available. The GPS module in Geotab GO6 and GO7 units have a jamming detection function that will trigger our device to report a debug log. This can be found in the log details of MyGeotab, appearing as: GpsJammingDetected.

For simplified monitoring of jamming and other GPS issues, an exception rule can be created in MyGeotab. This rule will generate an exception report and can trigger an alert or email for the event.

It is important to note that a GPS jammer disrupts GPS receiver functionality but all other functions are unaffected. The Geotab GO device will continue to gather and send information such as engine data, error codes, and auxiliaries, etc.

Credit/Author:  Vincent Scime, RMA Manager

Leave a Reply