"With a tin can, some copper wire and a few dollars’ worth of nuts, bolts and other hardware, a do-it-yourselfer can build a makeshift directional antenna. A mobile phone, souped-up with such an antenna, can talk to a network tower that is dozens of kilometres beyond its normal range (about 5km, or 3 miles). As Gregory Rehm, the author of an online assembly guide for such things, puts it, homemade antennae are “as cool as the other side of the pillow on a hot night”. Of late, however, such antennae have proved much more than simply cool.
According to Bobby Soriano, an instructor at the Philippine branch of Tactical Tech, a British organisation that teaches communication techniques to dissidents in five countries, such antennae can even foil government eavesdropping and jamming efforts. Directional antennae, unlike the omnidirectional sort, transmit on a narrow beam. This makes it hard for eavesdroppers to notice a signal is there."