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Engineers Build Satellite Jammer
cencini writes: "According to this article, U.S. engineers developed a device for $7,500 which generated UHF signals strong enough to jam mobile GPS systems. My question is, couldn't you build something like that for less?!" Update: 04/20 02:42 by H : The folks at New Scientist wrote with the original article - the device actually blocks UHF signals, but can be modified for other bands.
You're right about that 30 feet. With a nuclear device, I wouldn't be thinking 'oh, great, it's going to miss me by 50 feet'. At least, I probably wouldn't complete that thought. The military/government/TPTB put several limits on commercially available GPS units that render them useless on missiles. The first is an altitude limit of 60,000 feet. The other limit is a velocity limit (I don't know what it is.) Both of these limits are required on all GPS units sold, so that people can't use them for guidance systems. It is possible (I have access to one without the altitude limits) to get ONE of those limits waived, but it requred some governmental paperwork, and a very good reason. I would think it impossible to get one with both limits disabled, but I've never tried :).
The first post in the United States was established by Benjamin Franklin in 1775.
It's only 1 centimeter with post processing (the errors are made available the next day for correcting readings). The best that can be achieved immediately is 1-3 meter error, due to atmospheric affects.
...phil
...phil
"For a list of the ways which technology has failed to improve our quality of life, press 3."
ahh, the possibilities.
Bad guy launches missle relying on GPS.
Change just a little to steer it. "Here, missle missle"
A bit more. "C'mon, you're still drifting away."
Finaly change: "THere you go. You're on target now. GO say 'Hi' to
mommy . .
And little Mikey the Missle, thinking that he has cleverly found D.C.,
returns to his launcher in Bahgdad.
:)
hawk
Selective availability can be defeated using differential GPS. I got a Trimble dual differential receiver for a good price at a West Marine clearance sale, and my GPS reads out to a few meters uncertainty rather than 100 meters. Broadband jamming requires a whole lot of power and is thus less effective. Signal strength at any one frequency = power / bandwidth. GPS jamming is easier because there are a number of discrete frequencies. Military GPS uses spread spectrum with an undisclosed spreading sequence, so you must cover all frequencies in a wide band. It also uses tricks like processing gain to recover a usable signal in the presence of a lot of noise.
Hm. Anyone have a simple explanation of processing gain? I'm not enough of an RF person.
Thanks
Bruce
Bruce Perens.
Allow me to set the record straight.
Luddites were not scared of technology, although the word is often misused in this way. They were simply opposed to the humanistic changes that technology was bringing about.
To whit, if mobile phones had been available at the time, they would doubtless have used them as a tool for mobilising against the factory bosses.
Without contradiction.
Hamish
"Wise men talk because they have something to say; fools, because they have to say something" - Plato
I want something I can use in my car on the highway, possibly even directional so I can take out specific callers. It be great, but consider the driver weaving and cursing as he or she tries to figure out why the signal has gone dead. The problem with cell phones in cars isn't the fact that they exist, its that most people don't have hands free sets for them. As it is if you have people in the car you can and do talk to them, and for the most part when you need to concentrate on driving you fall silent. --locust
I'd like a cellphone jammer so I could get the clueless drivers to pay more attention to the road than the phone and notepad. I know the Japanese have a device that has about a 150 meter range that they use in theaters but I want something I can use in my car on the highway, possibly even directional so I can take out specific callers. There's got to be a couple of hardware hackers out there that could throw a design out open source for some field trials 8^)
Why, so you can start a war between Britain and China and get the exclusive media rights, of course! I mean, why else?
Editor Emeritus and Senior Writer, TeleRead.org
1: You can get differential GPS broadcasts now almost everywhere on the globe. You get a GPS receiver that picks up two signals: one from the satellites, and one from a ground base that knows its own location and broadcasts the difference between that and where the satellites tell it it is.
2: Not only did they not increase the offset during Desert Storm- they turned it off completely! The military GPS units are expensive and were in short supply, so many soldiers were using civilian units from home to find their way in the desert.
It's only a matter of time now before the offset is removed for good so the signals can be used for more accurate civilian tasks like surveying without all the expense to of the differential units or the expense to the military of their offset decoders.
The really scary thing about this jamming is that commercial airliners are starting to use GPS signals for navigation and bad weather landing.
It's a secret plot by women to get men to put down these things and actually get men to get out of the car and ask directions... or at least look at the road signs..
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ping -f 255.255.255.255 # if only
(rockets can't be steered, missiles can)
Excuse me? A rocket is simply a motor that generates thrust by hurling mass out the back. You can, too, steer a rocket: just point the exhaust nozzle in a different direction. A missile, on the other hand, is an object that is flying (has been hurled) through space (air, usually, but not necessarily) -- for instance, a spitwad is a missile (ballistic), as is a dart (ballistic), as is a Sidewinder (rocket powered). Some of these things are steerable and some of them aren't, but the words "rocket" and "missile" are not the appropriate ones to use to identify that distinction.
Oh, go on, check out my job.
GPS is so prevalent in the 'new', 'modern' battlefield that a device like this makes a lot of sense and I am sure that a lot of militaries have already built their own --or if not, they are starting up similar projects as we type...
Just some potential uses of a GPS jammer: Handheld and dashboard-mounted GPS is used all the time in tanks/helicopters/ships and by troops in the field. In most cases (i.e. outside of the US) these are *commercial* grade GPS, not US Military-grade GPS --i.e. they will be much less resistant to jamming.
The US Military, OTOH, has put so much faith into GPS, it's now using it to guide smart bombs and cruise missiles... so, you can see, the fact that the US Air Force itself has proven that it is feasible to jam GPS with COTS (commercial off-the-shelf) technology will be a HUGE deal to the defense planners of the world...
Now, I am not a EE, much less a DSP/GPS specialist, but from my knowledge of the system I am guessing that: a) the system described above won't be much use against fast-moving airborne GPS (fighters), and b) US Military-grade GPS can be affected just as effectively --as I believe that the US Navy is using an encoded higher time-resolution signal to achieve more accurate measurements. But if the signal is jammed, encryption won't be much use, right?
engineers never lie; we just approximate the truth.
as far as I understand, the error is mainly introduced into the altitude precision. this way civilians can get around, everyone knows where everything is, but no one can be certain they are going to be able to hit it if they launch a missile at it.
Daniel
I'm quite surprised it took this long. I heard a rumor about 2 years ago that a GPS jamming device was available in Russia with a 30 mile radius.
The NavSat network is a series of satellites w/ atomic clocks located in Geosynchronous orbit (so they hold steady above the equator) at over 20,000 miles distance. The timing pulses they send are low power, necessarilly so for them to last as long on their available power output.
Anyone with knowledge of which frequencies are used and the abillity to transmit their own quasi timing pulses in a manner which would interfere with at least 12 possible sats over the horizon at once could make their own jammer for much less.
It's easy to see that not many people are doing this, or GPS would be effectively knocked out in metro areas.
The Military can already jam or disable GPS at will. Part of the spec for GPS allows for them to disable or limit the civilian aspect of GPS during wartime and specific sorties.
Remember, the NavSat spec allows for a loss of accuracy for civilian GPS units (eg, you can't get better then 30 foot reliable position) but allows for 1 centimeter resolution for military units which know how to defeat the deliberate error. It's probably a timing sequence that milspec units can alter for.
What I've never understood about this is why. If it's to foil enemy cruise missles with civilian GPS units, 30 feet doesn't seem like that much of a difference for a nuke or large conventional explosive.
You can defeat this deliberate error, btw, by using three GPS units arranged equidistant with special software which knows the exact relative positions of the three GPS receivers and compensates accordingly.
Wow, this must be a record for old news on /. Anyone watching tv in the 80's knows that frequency jamming was perfected with the advent of knight rider's car, KITT. And it didn't take a team of U.S. engineers, either; it was single-handedly perfected by Bonnie in that roving semi.
The only anti-jam feature on most current GPS systems is the spread spectrum modulation. This is a complex topic in communications engineering and I realy don't have room to explain it in detail. However, the nub is that the signal is mixed with a high speed pseudo-random bit stream. This greatly increases its bandwidth (which BTW in this case does not provide any inherent signal to noise advantage) and causes the energy/Hz to drop below the thermal noise level. The receiver generates an identicle bit stream synchronised with the one on the satellite, but offset by the delay between satellite and receiver (this synchronisations is what's going on whilst your receiver is acquiring). When the second bit stream is combined with the signal from the satellite the energy is "de-spread" and basically gets piled back up into a narrow spike again. The inportant point is that any other signal will not correlate with the bit stream in the receiver. A wide band jammer stays wide-band and a narrow band jammer gets spread. In either case the recovered spike now sticks up above the jammer power. Generating a signal spread in the same way as that from the satellite doesn't help unless you can arrange for it to arrive at the receiver in exact synchronism, and to do this you need to know the exact distance between your jammer and the receiver. BTW, this pallaver is not just done for jam resistance, the synchronised bit stream is a critical part of the navigation solution. If anyone knows of an explanation of the above with diagrams, I suspect that many readers who are not RF engineers would find it useful.
Unfortunately, the above scheme only gives you a spreading gain of about 100. I.E. if your jammer is 100 times louder than the satellite then you still win. Since the satellites are a long was away, this is very easy to achieve.
One solution being actively persued by me and my colleagues in DERA's airborne antennas group and presumably the military research labs of other nations is the use of adaptive antennas. I won't even begin to try and explain how these work, but the bottom line is that by using several antennas combined via some clever electronics one can form nulls in the combined antenna pattern which point at the jammers. This makes the job of the jammer significantly more difficult, but not impossible.
BTW, there is nothing secret in the above. One of our industrial partners exhibited a prototype adaptive GPS antenna at the Farnborough Air Show at least 4 and possibly 6 years ago. Also, as might be expected, most current work in adaptive antennas is aimed at using them to defeat multi-path problems in mobile communications.
Everytime I take off a few days from my demanding job in the Valley, I like to head off to places like Yosimite and Yellowstone. But each month it seems that there are more and more untrained yuppies, grinding up the roads with their SUVs, displaying their designer hiking outfits (Tommy Hilfiger backpacks, anyone), and *always* carrying a GPS.
Granted, most of them have no idea how to actually *use* a GPS, or how to coordinate it with a map, but a few manage to figure it out if they haven't succumbed to heat stroke after the first mile or so (apparently they believe that there are Starbucks's scattered every 100 feet, just like in Manhattan). Having conquered the navigation system, they feel supremely condfident, and stride forward in their fashionable Donna Karan outdoorwear. But just sit back, and in a few hours, after wandering a few yards off the path, those newbies will be crying for help, and they expect the rangers to spend their time to go off and rescue them! How absurd! It is the *user's* job to be prepared, not the staff. Why won't they learn? The last thing we need is to devote our time, as a community, to digging these helpless newbies out of a trench they've buried themselves in. If you want to enter *our* territory, you better do it on *our* rules, pal.
I have this friend that has a navagation system in his truck. It's a nice system, between the GPS and a CD map of the east coast he is able to get just about anywhere.
But he uses it to get everywhere. He punches in the address for the grocery store (a mile away) and then punches in the address for back home. Maybe the novelty of a $3000 toy wears off slowly, maybe he is really that bad with directions.
For some reason the thought of wacked-out luddite guerrillas jamming his satellite signal on his way home from the corner market really cracks me up. I can just see him driving aimlessly for hours waiting for the navigation system to tell him when to turn.
Man-oh-man, a GPS jammer is a toy that may not lose it's novelty for a while....
[it is] believed that the latest generation of global communications satellites would be immune to similar home-built equipment, as they are "heroically resistant to jamming"
What does Heroically Resistant mean? I can see this satellite in orbit straining: must resist jamming! grr!It must be wonderful to be so naive that you trust technology to be heroic.
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[signature]
GPS contains the following capabilities:
Selective Availability adds some noise to the signal received by civilian receivers; military receivers can tune this one out using a specific cryptographic key. Selective Availability was actually turned off during Desert Storm, because the U.S. military didn't have enough "military" receivers for their troops!
Anti-Spoofing makes it cryptographically impossible to give a bogus signal to a military receiver.
The P code (P for Precision) gives very high precision to certain military receivers which have been equipped with receivers for the P code signal, in addition to the regular (CA, for Coarse Aquisition) code. The P code is not receivable by civilian receivers.
The GPS signal is jam resistant by being spread spectrum, but as the poster points out, there isn't any defense against wideband ("barrage") jamming.
The GPS signal coming from the sattelite has a deliberate offset so that they are never 100% accurate. This is because any moron with a steerable missile (rockets can't be steered, missiles can) that can carry a nuclear bomb can wire up a GPS as a precision-guidance system to deliver this missile very accurately.
In time of war, the offset increases dramatically, though supposedly that didn't happen during Desert Storm. I think it has something to do with the GPS capabilities of the enemy.
The military GPS was designed with anti-spoofing (just like IP spoofing) and anti-jamming (I think it dynamically changes frequencies, but not sure) capabilities, but these are not built into the civilian models.
The military GPS can be given a cryptological key that significantly increases the accuracy and enables all the other Electronics Counter-Countermeasures (ECCM--Electonic Countermeasures, or ECM, is what normal people call jamming, ECCM is what you do to combat ECM).
Of course, once you start barrage jamming (blocking out the entire radio spectrum), all bets are off. Nothing can make it through barrage jamming.
I do what the voices on my console tell me to do.