I went to a GnuRadio conference a few years ago where a lot of presentations were on directional tracking of signals. One huge issue is that truckers are using GPS jammers that plug into the cigarette lighter socket to block the truck tracking systems from knowing that they are driving outside of their legal time limits. One trucker has left his jammer plugged in for a day or two. The nearby port was entirely shutdown until authorities found the jammer because the massive ships couldn't navigate the tight quarters of the port without GPS. One project was using cameras along with multiple antennas to attempt to track who was driving past a particular overpass with a jammer turned on. A cigarette lighter socket has the potential to put out tens of watts out RF power which can almost certainly jam anyone that can't use the military anti-jam GPS channels.
It's not so easy to find them when they are intermittent and mobile. The prime example is truck drivers who want to briefly disable the GPS tracking systems their company put on their trucks. One of these guys was occasionally driving past a major airport...
If one thought the FBI (or a partner or ex-partner) was prone to putting a GPS tracker in one's car, one might grab cheap jammer from a Chinese e-commerce site for $20.
This is all for simple omni-directional jammers, whether chirp or wideband. Directional jamming of an aircraft is simple, and let's you put lots of energy on the target and also mask your transmission from surveillance systems. Sophisticated systems don't simply overwhelm the receiver, they trigger decoding errors, and with much less power.
The full scope of the problem is masked at present. It is relatively trivial to provide fake GPS signals so as to seduce a target receiver (e.g. mobile phone, plane GPS system) to believe it is somewhere else entirely, or off track by hundreds of meters. If a plane believes it is elsewhere, and transmits that via ADS-B, it could easily cause havok.
Jammers are cheap and since a lot of expensive gear has GPS tracking these days, thieves are using simple jammers you plug into the cigarette outlet in cars.
This is increasingly becoming a larger problem since they jam a relatively large area.
> Send the remote shutdown instruction over a suitably designed radio link and jamming becomes utterly impractical.
Unless the radio link must be always-on for the vehicle to move, I think you've underestimated what is required to construct an RF link that is impervious to interference.
We still have problems with shmucks using GPS jammers to prevent employers from tracking them halting traffic at major airports: http://www.insidegnss.com/node/3676
"It took the FAA and FCC from March 2009 until April 2011 to locate a GPS jammer operated by another trucker on the New Jersey Turnpike, according to a presentation by John Merrill, Department of Homeland Security program manager for position, timing, and navigation, at the 2012 Telcordia-NIST-ATIS Workshop on Synchronization in Telecommunication Systems."
the problem is that the legitimate GPS signal is ridiculously weak, and generally speaking, to reliably jam, you need a significantly stronger signal. (well, and compared to a solar-powered transmitter on a satellite, it's pretty hard not to have a significantly stronger signal) I'm not a RF guy myself, but I hang out with a bunch of them. Guaranteeing that your jammer only had a range of a few feet sounds... difficult.
I personally know people that have had problems with their systems that have been traced back to truckers with GPS jammers.
i don't understand why someone would jam gps. if you want to disable your own transmitter, you can physically disable it. jamming is only useful to unilaterally disable someone else's transmitter, and i don't know why anyone would want to do that outside of a war...
I don’t think you can really do that. Jamming mostly targets a receiver. Disrupting the signal that’s emitted by a tracking device would make you really easy to triangulate and find.
IIRC, there exist things for GPS called "null steering antennas" that allow a receiver point a "null" at a jamming source to block it. I believe they're considered controlled munitions by the US government.
"Agents from the FCC used direction finding techniques to find that strong wideband emissions were coming out of a blue Toyota Highlander SUV driven by Humphreys."
This I find interesting and am curious what devices they had to obtain in order to accomplish this.
I used to work for a telco that, to this day, continues to have this very issue with _someone_ in a remote rural location. By the time the NOC can inform local law enforcement the jammer has left the area, seemingly impossible to track.
You are forgetting about the phased nulling. Military GPS has been including jammer detection in the firmware for a long time. I remember my handheld unit constantly annoying me anytime the IED jammer (which was waaaay more than 1 watt of rf) went active... 2005ish - it would simply mask the signal coming from that direction and continue to provide positioning data.
Also, "jamming" can include sending distorted signals. These distortions can be a spoofed or malformed packet of data. Knowing what happens when a navigation tool suddenly thinks the vehicle is on the other side of the world is important. As is, ensuring that a garbage signal won't crash it.
Tell that to the truckers who accidentally cause panic in a metropolitan area when they forget to turn off the jammer they use for fudging hours and miles. Those signals are very weak by the time they get down here, and easy to override. It's just illegal.
There are no legal GPS jammers in the USA. In fact, the one of two things that will get the FCC on you really bad is to mess with GPS or Cell Phone signals.
For Example, US Prisons want to jam Cell Phones but the FCC says no way.
This will lead to an arms race with deploying cellular, GPS and wifi jammers. You can order them online right now for low prices, at low power they are very unlikely to ever be investigated.
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