The location of a chirp jammer in the car on Shelter Island that was used to simulate the effects of GPS jammer in San Diego Bay. GPS signals are transmitted at power equivalent to that of a standard light bulb. They are expected to travel more than 20,000 km and still be suitable for high-precision position calculations. In most cases, the signals arrive relatively intact, but can hardly be distinguished from the thermal background noise and can be ducks for any passing interferer.
The use of GPS jammers is strictly prohibited, but their effects can be assessed using a GPS simulator. Using the example of the port of San Diego, a simulator was programmed to generate the GPS signals that a receiver on a boat at that location would see. The interference of GPS signals was mimicked by mixing the simulator signal with that of a jammer. With the jammer in the location shown in Figure 1 and the GPS receiver on a boat near the bay, the effect of interference across the bay could be extrapolated using standard models of radio wave propagation.