It’s illegal to own or operate a GPS jammer in the United States for many valid reasons. More importantly, it threatens many systems us humans find relevant. If GPS goes down, how will people get around cities without getting lost? (Google Maps works so well for public transit.) It’s not surprising that the biggest threat to GPS is actually its owners: the US government.
GPS frequencies are very weak, so any slight amount of interference can cause the signals to fail. LightSquared, a company that plans to deliver wireless broadband over satellite, operates in frequency ranges adjacent to those used by GPS. Many people involved with GPS were surprised when the FCC gave tentative approval to LightSquared, essentially setting up GPS for failure. Apparently, the normal processes were circumvented for possible political favors.
Garmin recently tested GPS near the LightSquared transmitters and found jamming at 3.57 to 13.76 miles with a loss of location fixing from 0.66 to 5.6 miles away. Even the US Air Force thinks the FCC has gone crazy. Hopefully, this doesn’t interfere with my hooking up on Ditto.