Bill wrote: "Someone stated on this forum that the government is selectively targeting areas such as military bases, power plants, etc. and inducing GPS error in those zones only. How is this accomplished? Do they send out jamming signals in a given area? I doubt that is possible. " _____________________________________ Yep, easily done. Matter of fact, someone awhile back posted the exact frequency to broadcast on to jam it. I won't be as accomodating here... if anyone really wants to, they'll have to find it for themselves! ;) Remember, the GPS signal is very weak to begin with, easy to override it. -- __________________ Keith Eat well, stay fit, die anyway.

Keith, Sorry I'm still not convinced. If it's that easy to jam, DOD was wasted a lot of time and money. After all the system wasn't built for boaters and hikers. I know that the signals my GPS receiver sees are very weak, BUT they are very, very complicated. So the receiver is not easily fooled. In fact because of the pseudo random code, one of the key factors that makes GPS work, it's virtually impossible to induce an error only in a selected area. That's key to the whole system. Understand I'm not saying that errors can't be induced in the whole system or even in one satellite, but when that is done it effects the whole range covered by the system or the selected satellite(s). The system won't let me choose an area, say a 10 mile radius around a power plant, within that range to target that error. Just think for a moment. WAAS works the same way as GPS. In fact it's a refinement of GPS with additional satellites furnishing more data, therefore more accuracy, at greater update rates. The FAA is developing WAAS to land airplanes unmanned. If it is possible to jam as easily as stated, terrorist will have a "ball". Nope, somebody is going to have to have to explain to me how GPS is jammed in a selected area. I don't believe simply tuning a transmitter to a certain carrier frequency will do it. I think some real sophisticated modulation is going to have to be done to that carrier before it fools my GPS into thinking its in South America instead of Three Mile Island. Bill Cooke M/V All The Marbles Roughwater 41

John Gill replied: William and List, I do not know how the military is doing the jamming, but I can tell you that when we went down the ICW from the Chesapeake Bay this past Fall, our GPS showed us going 40 knots one minute and 3 knots the next and at one point our Lat / Lon indicated that we were in South America -- that was going past the Norfolk Navy Base, about 3 miles before and until 3 miles past the base. We had the same "problem" going by the Marine Base and by a Submarine Base. Pure coincidence??? I doubt it. A friend of ours experienced the same "problem" taking his boat to the New Jersey shore from the Chesapeake Bay, when he looked around he noticed a Nuclear Power Plant nearby. Another coincidence. In each of these cases, the "problem" cleared up within only a few miles past the possible terrorist targets. Remember that we had errors introduced for several years and all of a sudden no need for errors -- even after 9/11??? If you don't think that the USA has superior equipment, then guess again. John ___________________________________ William Cooke wrote: > Keith, Sorry I'm still not convinced. If it's that easy to jam, DOD was > wasted a lot of time and money. After all the system wasn't built for > boaters and hikers. > I know that the signals my GPS receiver sees are very weak, BUT they are > very, very complicated. So the receiver is not easily fooled. In fact > because of the pseudo random code, one of the key factors that makes GPS > work, it's virtually impossible to induce an error only in a selected area. > That's key to the whole system. > Understand I'm not saying that errors can't be induced in the whole system > or even in one satellite, but when that is done it effects the whole range > covered by the system or the selected satellite(s). The system won't let me > choose an area, say a 10 mile radius around a power plant, within that range > to target that error. > Just think for a moment. WAAS works the same way as GPS. In fact it's a > refinement of GPS with additional satellites furnishing more data, therefore > more accuracy, at greater update rates. The FAA is developing WAAS to land > airplanes unmanned. If it is possible to jam as easily as stated, terrorist > will have a "ball". > Nope, somebody is going to have to have to explain to me how GPS is jammed > in a selected area. I don't believe simply tuning a transmitter to a certain > carrier frequency will do it. I think some real sophisticated modulation is > going to have to be done to that carrier before it fools my GPS into > thinking its in South America instead of Three Mile Island. > Bill Cooke > M/V All The Marbles > Roughwater 41 > > _______________________________________________ > Trawler-world-great-loop mailing list > Trawler-world-great-loop@lists.samurai.com > http://lists.samurai.com/mailman/listinfo/trawler-world-great-loop

on 2/7/02 11:15 AM, William Cooke at cooke_w@bellsouth.net wrote: > Understand I'm not saying that errors can't be induced in the whole system > or even in one satellite, but when that is done it effects the whole range > covered by the system or the selected satellite(s). The system won't let me > choose an area, say a 10 mile radius around a power plant, within that range > to target that error. They jam by localizing the jamming signal to a specific area. This could be done by hiding a transmitter in the area, or (I'm speculating) by directing a narrow cone of RF interference from a high-altitude plane or a top-secret military satellite using a directional beam antenna. We don't need to confuse the GPS into thinking it's somewhere it isn't; just need to confuse it enough that it can't lock into the real signal; in other words jamming it. -- David KoJen http://www.bicnet.net/~scarabe/solisMaris