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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.
RF jamming is hardly a new technology, and the people who came up with GPS aren't stupid. This possibility has without a doubt already been considered and dealt with - give them a little credit here. Jamming a spread-spectrum carrier means using a broadband jammer, which is expensive, sucks a lot of power, generates tons of heat, and has a paltry range. Even a theater-based GPS jammer would be inconcievable; barring a massive technological investment, at most only a small portion of the theater could be jammed (realistically). Also, neither smart bombs nor cruise missiles are solely reliant on GPS.
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I think there is a world market for maybe five personal web logs.
[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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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.