3 ms·

> When using GPS receivers in city urban canyons with tall buildings, the shadowing and multi-path effects results in poor GPS signal reception and jammer range

> When using GPS receivers in city urban canyons with tall buildings, the shadowing and multi-path effects results in poor GPS signal reception and jammer range can be even hundreds of meters at street level. That was something that I haven't thought off. The jammer will have less interference from shadowing and will benefit from reflection of buildings, so in a city environment it interferes more than in open air.

olympus 9y ago
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.

olympus 9y ago

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.