The G120 supports GPS Jamming and GPS interference detection. The available parameters are split into 2 tabs in OEM.
The GPS Jamming (Adv) parameter sets what constitutes "Jamming" or "Interference".
1 = Interference Parameters
2 = Jamming Parameters
The G120 represents "Interference" with a Digital Input. Defaults should generally work well, and are best left untouched unless you know what you are doing.
GPS signals are broadcast at specific frequencies, and GPS receivers (the G120) are tuned to pick these up. Generally, they won't be very strong (they are coming from satellites orbiting about 20,000km away!). So if the module detects signals in this frequency range that are much stronger, or that make up a large proportion of the total signal, it can consider this interference and report it.
When the device is in trip, it will leave its GPS on, getting regular fixes and calculating heading, speed, odometer etc. with this data. So if GPS signal is lost for a long time, there is likely a problem, so we flag jamming. This is set by the Warning Timeout parameter.
The GPS Jamming I/O (Adv) parameter determine what actions to take should jamming or interference is detected. By default, the device will flag interference and record a log.
With these parameters we can set which digital inputs the Interference and Jamming flags are mapped to. By default, Interference is mapped to input 7 and Jamming is mapped to input 8
As soon as jamming/interference is detected, a log is created - this will appear as a Digital Input Changed log. We can set the device to immediately upload if this is detected - however when in trip, the device will be connected to the network anyway - so even with this not set, if detected in trip this will be uploaded immediately.
Jamming/Interference In OEM Server
If JAMW log reason is seen in the device logs, then GPS Jamming/Interference was detected.
Jamming/Interference In Telematics Guru
Alerting on GPS Jamming
The G120 is already configured to report Jamming and Interference by default. So we can just set up an alert in TG if we wish to be notified. From Admin> Alerts> New Alert (Advanced), set to alert if either of the following input is active.
Note, these inputs may become active a bit more than you think. Other electrical signals may cause interference. So it might not be malicious operators with jammers each time you get an alert.
Display on the Live View
We can edit the I/O mappings to display if interference or jamming is detected on the live view
Check for evidence of Interference/Jamming in the Telemetry
Maybe we have some mysterious events where trips weren't recorded. We can check if the IOs are active in the telemetry.
In telemetry, there are 32 total bits. However in binary, we start counting from 0, right to left, meaning we have bits 0-31. So working right to left 0, 1, 2, 3, 4, we can see bit 7 highlighted below.