The South Korean government has reported that electronic jamming signals from North Korea were affecting communications and GPS signals for passenger aircraft. So far, there has not been a serious threat to safety because the pilots were able to use supplemental navigation devices. But how does a group disrupt signals from GPS or other communication systems in the first place? The simplest way to is to drown them out in a barrage of other signals, said Adrian Graham, a consultant in electronic warfare and the author of a textbook on the subject. That means sending out a radio signal over a wide range of frequencies similar to the ones that GPS uses. Because GPS signals are not that strong, barrage jamming is rather like blasting music in a room and drowning out conversation. Another method is to drown out the satellite signal by beaming a narrowband signal directly to the GPS receiver, if its location is known. NEWS: North Korea GPS Jamming Affects Flights "Ev...