ghosting

Ghosting in television reception is a shadow or duplicate image that appears displaced and slightly blurred behind the main picture. It occurs when the broadcast signal reaches the receiver via two or more paths of different lengths, typically one direct path and one or more reflected paths bouncing off buildings, terrain, or atmospheric layers. The delayed copies arrive microseconds after the primary signal, and because they are fractionally out of phase with the direct reception, they create visible artifacts rather than reinforcing the desired image.

The effect is most pronounced in VHF and UHF television, particularly in fringe reception areas or near large reflecting obstacles. A broadcast tower might send a signal directly to an antenna, while a reflected signal from a distant hillside or tall structure arrives perhaps 100 to 200 nanoseconds later. This time offset translates to a spatial offset on the screen, producing the characteristic ghost image offset horizontally from the main picture. In analog television systems, the degree of ghosting depends on the amplitude and phase relationship of the reflected signal relative to the direct signal.

Multipath reception itself is unavoidable in most real-world environments, but ghosting severity depends on equipment and site conditions. A directional antenna aimed away from major reflectors reduces the amplitude of delayed signals. In some cases, carefully positioned reflective surfaces or active phase-cancellation circuits can minimize the effect. However, consumer receivers of the mid-20th century had limited tools for mitigation. Modern digital television systems handle multipath much more robustly through error correction and adaptive equalization, making ghosting far less visible even when multipath energy is significant.

The term ghosting draws directly from the visual phenomenon: the secondary image appears as a faint, transparent ghost of the primary picture. The word entered broadcast engineering vocabulary in the 1940s and 1950s as television reception became widespread and multipath became a common complaint. Technicians and antenna specialists became skilled at diagnosing ghosting by its characteristic visual signature and recommending antenna repositioning or higher gain directional designs.