Pretty much. Here's an expanded, but still very simple way to think of the way this noise jamming works: - A GPS receiver needs a signal/noise ratio above X d

Pretty much. Here's an expanded, but still very simple way to think of the way this noise jamming works: - A GPS receiver needs a signal/noise ratio above X dB to get a lock - Higher gain antennas, more sensitive receivers, and higher powered signals add to the numerator (good) - Antennas with smaller sidelobes (often a consequence of a high gain antenna or nulling antennas), and better signal processing reduce the denominator (good) - There is a pretty good S/N margin when using a modern receiver with a good antenna in open space - Shadowing reduces the signal strength and thus reduces the numerator (bad) - Multipath effects increase noise, and thus increases the denominator (bad) - Jamming increases noise, and thus increases the denominator (bad) - Jamming can be improved by cranking up tx power or using a higher gain antenna (or both) - In open space, a jammer must overcome the entire S/N margin by itself. GPS systems are so highly optimized (very good algorithms) and have such a big S/N margin that you can often get a lock just by putting the GPS in a hole and that nulls enough of the jamming. - In a city, shadowing and multipath eat into the S/N margin by quite a bit, so the jammer doesn't have to do as much. Sometimes the urban environment is so bad that GPS can't get a lock even without a jammer. - Jamming strength decreases with the square of the distance (or 2x when talking in terms of dB, which are logarithmic) - The margin reduction by the shadowing and multipath benefit the effective distance by the square of the reduction (or 2x when talking in terms of dB) - So any natural jamming benefits the jammer by allowing it to operate much further away or operate at a lower power. There isn't much you can do to reduce natural jamming like multipath or shadowing other than moving to a different location. edit: grr, I hit tab and enter before finishing.