Sat-nav systems under increasing threat from 'jammers'

Jamming GPS is harder than most folks think (says the Old Crow)...

Yes, you don't need a lot of power, because the signal from the birds is so low level in the first place.

But--

You've got to get your jammer up in the air, *above* the GPS receivers you want to spoof/jam. The patch antennas used by most receivers drop off significantly within 5 degrees or so of the horizon (purpose-built marine antennas are different and are designed to go to or a little below the horizon).

Random (incoherent) jamming isn't that hard, filling the desired frequency range with noise. To be effective, though, you've got to noise-jam the channel for long enough to get receivers in the area to go to a warm-start fallback, or even a cold start. Just about every consumer GPS available these days can take a 30 second to 2 minute signal drop without a problem, as those drops are common in urban canyons, tunnels, overpasses, and the like. That means an omnidirectional antenna, the transmitter at altitude, and power (a half watt or more, 2 watts is a good level).

Spoofing, though, generating something that looks like a constellation of GPS signals, is a different story, and takes some computation and some smarts. Not likely to be done your local weekend technologist. And the sneakier you want to be, the more computation is involved, and the more precise the signal generation needs to be. A noise jammer could fit in an Altoids tin. A spoofer is more likely to be breadbox sized, and two or three orders of magnitude more expensive than the noise jammer.

And if you're thinking movie-threats, like "I want any GPS in the area to read 300 meters offset at a bearing of 65 degrees" -- you are talking about a very complex device!

And once you've got it working, you've got a transmitter operating in a known frequency spectrum, deliberately trying to upset people who have access to systems designed specifically to hunt down your transmitter and turn it off permanently, violently, and from a distance.

Bluetooth and Wi-Fi jammers, even cell phone jammers, those are fairly easy. GPS is hard, and has a different class of people protecting it.

You may want to have a look at this then, 'old crow' ; http://www.theregister.co.uk/2010/02/23/car_theft_gps_jam/

That's putting the jammer on top of the car's GPS antenna. That's simple and easy. A metal bowl or metal foil covering the antenna works, too. On Mercedes and BMW (and Mini) the antenna on the top of the car is a combo telephone/gps/FM and sometimes sat radio antenna. Magnetic mount your jammer within a meter of that and drown out the GPS.

Move a few meters away, and you're no longer in near field; a much different story -- note the comment that 2 watts is only good for a few meters -- 2 watts on bluetooth or Wi-Fi frequencies (2.4 GHz) should wipe out most devices within a few *hundred* meters.

cheers--

I guess that would depend if the device is directional, or not though.

However, it would seem that anyone wanting to jam the GPS signal fully would need to be a fixed location to continually disrupt it, or, have a mobile unit that drives around to attempt to avoid getting located.

I would think the former would be in a country other than the one being messed with. As for the latter, yea, if it was in NA, it would be hunted and killed very quickly!

But, remember that post about the GPS' that were getting confused on or near bases? I stated then, this was a possibility, and I may have been correct.

Is it the gps is confused/jammed or was the database/map tweeked to make the feds happy?

I would go with the latter.

Another thing to keep in mind is that not a lot of consumer electronics are designed to operate in the presence of strong RF fields -- such as what you'd encounter near air force bases in particular.

There are a lot of consumer gadgets that misbehave if nearby when I'm transmitting on the 144 or 440 MHz ham bands. I had a radar detector that went off when I transmitted on 144 MHz -- that one went back quick! A friend had a handheld GPS (don't remember the brand, it was a few years ago) that locked up if he tried to use it in my car and I transmitted on 440 MHZ -- he'd have to take the batteries out to get it to reset.

Newer electronics are better, as the European Union requires susceptibility testing (as do SAE automotive standards).

The US FCC only cares about emissions.

Bummer