Nope, you just need a suitably tuned HARM.
End of problem.
Posted on 11/08/2003 4:12:31 AM PST by talk2farley
I am posting this in response to concerns raised in regards to the Russian-made GPS jammers the military recently came up against in Iraq. Hopefully, with will dispell some of the myths regarding how they work, how them ilitary works against them, and just how effective they are under ideal circumstances.
First, a word on GPS. Since GPS went public, circa 1995, their have been two signal broadcasts. The original signal, broadcast at approximately 1500 MHz, which is now used for civilian localaization. So I will now refer to this as the Civilian signal. Finally, the bloc two (or L2) signal, which was deployed circa 1995 as a more accurate, more reliable, less jammable wavelength, which is now used for Military purpose. The L2 frequency is approximately 1200 MHz, and is encrypted.
This has lead some to speculate that, being encrypted, the military signal is proofed against jamming. This is WRONG.
The sole difference between the militaries L2 frequency and the Civilian frequency is approximately 300 MHz. Yes, it is encrypted. But this encryption simply prevents you or I from using the signal to correlate a position. The encryption does nothing to protect against jamming. This is elementary. Any frequency may be jammed. The way to decrease the efficecy of jammers is to develope countermeasures (jammer-jammers, the reason being that jammers work by broadcasting their own radio signal which interferes with the source signal coming from the jammer, in effect jamming it to prevent it from jamming ITS target, the GPS signal), to change the frequency (military radio communications can hop frequencies quite effectively, but this is impractical for use with GPS), or to broadcast a narrower signal, making it more difficult to aquire and jam.
The next bloc of modular upgrades to the GPS system (dubbed L5) will move military sats to a much narrower signal (far lower on the radio band) and civillian sats will phase into the L2 block. This will give the military sats a signal which not only much more reliable, but also much more difficult to jam than the current L2 bloc. And since the L2 block is more reliable and more difficult to jam than the aging Civilian bloc, which has been in use since the '80s, civilian GPS infrastructure will gain its own protection.
As for jammer-jammers (the countermeasures discussed above), Ive heard nothing official on the subject, but Im sure the military has already begun testing if not deploying such devices. One simply need isolate the frequency of the jamming device. Because GPS broadcasts on a constant frequency (again, ~1200 MHz for L2), the jammer must likewise broadcast on a constant signal. This makes isolating its frequency, and developing a suitable countermeasure, extremely simple. There is an obvious and inherent problem with this. It can lead to an endless chain of jammer-jammers. This was a problem that came up during th Cold War, as both sides struggled to out-jam the opposing sides radar jammers and their radar jammer jammers. Eventually, the American solution was to simply broadcast a RADAR beam too powerful to effectively, and totally, jam. However, this option is not applicable with GPS.
Finally, a word on the actual effectiveness of the jammers themselves. The radio signal originates 12,000 miles above the earths surface. The jammer sits ~3 feet above the earths surface. Given this disparity, and giveing the jammer an effective radius of, say, 5000 feet (a rather liberal estimate which would require a rather powerful jammer), that gives us a vertical window of approximately 600000 feet. Bearing this in mind, you can see how GPS jammers would do little to interfere with GPS guided munitions, which would function fine above 5000 feet. As they neared the target, which was protected by a GPS frequency jammer, they would switch to their redundancy backups, which are inertia-based.
Short of controlling gravity, you can't do much to screw these old fashioned goodies up.
However, there is a reasonable threat to ground-based GPS recievers which are operating within 5,000 feet of the source jammer. For this reason, it would be prudent for the United States (and cheapest, given the alternatives discussed above) to simply target and eliminate the jammers from the air, where they are not effective.
Hope that clears everything up. Basically, there is little threat posed by these devices. They are easy to find (anything which broadcasts a wideband signal, be it UHF, VFH, LF, RADAR, or even Microwave, must give its position away), and thus easy to target given todays precision technology.
Nope, you just need a suitably tuned HARM.
End of problem.
Your obvious extensive knowledge of the subject has just stunned us into silence! One hardly knows where to start!
Nah. The just need the Trace Buster Buster ... Buster.
"The jammer sits ~3 feet above the earths surface"
What are these result if the jammer is at 3000 feet above the earths surface. (on the side of a mountain overlooking a wide valley) I'm thinking Sierra Mountain Range, with the Rockies they could probably get 7k or 8k above the lower levels.
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