In television, a ghost is a replica of the transmitted image, offset in position, that is super-imposed on top of the main image. Common causes of ghosts are, Mismatched impedance along the communication channel, the technical term for this phenomenon is ringing. Multipath distortion, because radio frequency waves may take paths of different length to reach the receiver, by getting a better antenna or cable system it can be eliminated or mitigated. Note that ghosts are a specific to the video portion of television. SECAM TV uses FM for the signal, hence ghosting only affects the luma portion of its signal. TV is broadcast on VHF and UHF, which have line-of-sight propagation, and easily reflect off of buildings, mountains, the audio portion uses FM, which has the desirable property that a stronger signal tends to overpower interference from weaker signals due to the capture effect. Even when ghosts are particularly bad in the picture, there may be little audio interference, for instance, plugging in an additional aerial to a TV which already has a communal TV aerial connection can cause this condition. Ghosting is not specific to analog transmission and it may appear in digital television when interlaced video is incorrectly deinterlaced for display on progressive-scan output devices. Ghost-canceling reference Onion skinning http, //www1. electusdistribution. com. au/images_uploaded/tvrecepe. pdf http, //www. ofcom. org. uk/static/archive/ra/publication/ra_info/ra323/ra323. htm#15
A simulated example of severe ghosting in an analog TV broadcast.
A "ghost eliminator" sold to consumers in the 1960s and 70s to make ghosting less visible. This unit was a simple resistive attenuator.
Ideal situation for TV signal propagation: The signal leaves the transmitter (TX) and travels through one path to the receiver (the TV set, which is labeled RX)
An object (an aircraft) complicates the system by adding a second path. The signal arrives at RX by two paths which have different lengths. The main path is the direct path, while the second is a reflection from the plane.