Editing Van Eck phreaking (section)

== Basic principle ==

Information that drives the [[video display]] takes the form of [[high frequency|high-frequency]] electrical signals. The [[oscillating|oscillation]] of these [[electric currents]] create [[electromagnetic radiation]] in the [[radio frequency|RF]] range. These [[radio waves|radio emission]]s are correlated to the [[video]] image being displayed, so, in theory, they can be used to recover the displayed image.

In a CRT, the image is generated by an [[electron beam]] that sweeps back and forth across the [[Computer monitor|screen]]. The electron beam excites the [[phosphor]] coating on the glass and causes it to glow. The strength of the beam determines the brightness of individual [[pixel]]s (see [[Cathode-ray tube]] for a detailed description). The electric signal that drives the electron beam is amplified to up to around one hundred volts from [[Transistor–transistor logic|TTL]] circuitry. This high-frequency, high-voltage signal creates electromagnetic radiation that has, according to Van Eck, "a remarkable resemblance to a broadcast TV signal".<ref name="emr" /> The signal leaks out from displays and may be captured by an antenna, and once [[Analogue television synchronization|synchronization pulses]] are recreated and mixed in, an ordinary analog television receiver can display the result. The synchronization pulses can be recreated either through manual adjustment or by processing the signals emitted by [[electromagnetic coil]]s as they deflect the CRT's electron beam back and forth.<ref name="emr" />