For instance, plugging in an additional aerial to a TV which already has a communal TV aerial connection (or cable TV) can cause this condition. If the ghost is seen on the left of the main picture, then it is likely that the problem is pre-echo, which is seen in buildings with very long TV downleads where an RF leakage has allowed the TV signal to enter the tuner by a second route. TV is broadcast on VHF and UHF, which have line-of-sight propagation, and easily reflect off of buildings, mountains, and other objects. SECAM TV uses FM for the chrominance signal, hence ghosting only affects the luma portion of its signal. Even when ghosts are particularly bad in the picture, there may be little audio interference. 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. Note that ghosts are a problem specific to the video portion of television, largely because it uses AM for transmission. By getting a better antenna or cable system it can be eliminated or mitigated. In addition, RF leaks may allow a signal to enter the set by a different path this is most common in a large building such as a tower block or hotel where one TV antenna feeds many different rooms, each fitted with a TV aerial socket (known as pre-echo). Multipath distortion, because radio frequency waves may take paths of different length (by reflecting from buildings, transmission lines, aircraft, clouds, etc.) to reach the receiver. The technical term for this phenomenon is ringing.
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