The U.S. Department of Transportation will hold a workshop on GPS harassment and fraud in the marine environment on the afternoon of December 3. Speakers included Maersk Line Captain, Assistant Assistant Secretary for Research and Technology Diana Fuchtlot; and representatives from the National Security Council, the Maritime Administration and the U.S. Coast Guard.
While GPS jamming and fraud are an issue in many transportation and critical infrastructure areas, they are often most pronounced in maritime transportation. This is because the Automatic Identification System (AIS) for collision avoidance and traffic management of large ships transmits position data based on GPS output. These transmissions are picked up by coastal networks and satellite systems. AIS data is usually available for a fee or easily accessible to the general public.
Ships in Russian waters are disguised as inland airports, ships in Chinese ports are reported to be inland and maneuvering inside government buildings, and ships in parts of the world broadcast their positioning circles thousands of miles away in Northern California. The three highest cases offered in recent years. In 2019, the U.S. Coast Guard listed GPS signal jamming as an IMO “urgent issue.” In February, President Trump issued an executive order on the incumbent use of positioning, navigation and timing. The workshop is part of an effort by the federal government and an important part of educating the public about the pitfalls associated with over-reliance on GPA. There is a fee for seminars, but participants must register. Pre-registration can be stopped.
The visible top plate is actually a metal shield. A little convincing, we can look inside and see a staggering number of components packaged in a 9mm x 7mm area.
The fundamental working principle here is that the control pin of the VCO (marked as VC on the silkscreen) is connected to the input of the 555 timer on the other side of the board. The signal from the 555 modulates the input of the VCO and generates noise, centered on the GPS frequency of 1,575 MHz.
After connecting the oscilloscope to the VC pin, we can see that the 555 timer generates a 133KHz sawtooth signal. Adjusting this signal allows you to change the frequency range of the GPS blocker. But without a VCO’s datasheet, it’s hard to tell how far you can move it. But since these may be the cheapest components available, they may not be too far away.
It’s worth looking at the small four-pin device labeled Q6 on the top of the motherboard. As the high frequency signal goes from the VCO to the center pin of the antenna connector, it is in the path of the high frequency signal, which would be a logical place to place the amplifier. But it could also be a diode to protect the electronics from everything the antenna picks up.