page_title: Ghosting (television)
section_title: Analog ghosting
hierarchical_section_title: Ghosting (television) / Analog ghosting
caption_attribution_description: English: A "ghost eliminator" designed to reduce ghosting in over-the-air consumer television reception, made by w:Radio Shack under its Archer label. Devices like this were sold in the 1960s and 70s. The unit measures 95 x 68 x 43 mm and contains a resistive attenuator with a variable potentiometer between the antenna and receiver File:Pi type unbalanced attenuator circuit.jpg. According to a review in Popular Science, April 1972, pp. 75-76, the unit sold for $3.99 and was of limited utility.
context_page_description: In television, a ghost is a replica of the transmitted image, offset in position, that is superimposed on top of the main image. It is often caused when a TV signal travels by two different paths to a receiving antenna, with a slight difference in timing.
context_section_description: Common causes of ghosts (in the more specific sense) are:
  Mismatched impedance along the communication channel, which causes unwanted reflections. The technical term for this phenomenon is ringing.
  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. 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). By getting a better antenna or cable system it can be eliminated or mitigated.
  Note that ghosts are a problem specific to the video portion of television, largely because it uses AM for transmission.  SECAM TV uses FM for the chrominance signal, hence ghosting only affects the luma (video) portion of its signal. TV is broadcast on VHF and UHF, which have line-of-sight propagation, and easily reflect off of buildings, mountains, and other objects.
  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.
caption: A "ghost eliminator" sold to consumers in the 1960s and 70s to make ghosting less visible. This unit was a simple resistive attenuator.
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