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For Analog TV the Answer is:
The TV picture image is being received multiple times
a fraction of a second from the main picture signal.

For Digital LCD TV the Answer is:
The speed at which the LCD screen up dates...

Analog & DigItal TV

Why?
Any station can have ghosting as the TV signal is bounced off objects like buildings, overpasses, hills etc. Your analogue TV receiver picks up the "main TV signal" as well as any "TV signal echoes" and displays them as ghosts. TV Stations use "high power" to get the signal into your home, so people with rabbit ears, "in roof" antenna and those that use wet pieces of string can receive some watch-able form of picture & sound; this in turn creates powerful signal echoes.

It is a trade off to maximise people watching (for advertising revenue) over quality watch-able signals.

DiGiTaL TV receivers eliminate ghosts but the ghosts have not gone away, the DiGiTaL TV smarts filter the signals and track on the strongest one. If a ghost and the main signal are of equal strength, the TV smarts won't find a picture and report "no or bad signal".

LCD TV - (technology limitation)
Can display a false ghost effect when fast moving objects are shown on screen, a type of trailing effect which is caused by the little Red, Green & Blue LCD cells not switching off/on fast enough. It is not a fault with the TV it is a limitation of the technology. As the LCD TV gets older this effect may be more noticeable or less depending upon the light conditions in the TV viewing room and back illumination of the LCD screen (the fluorescent tubes or LEDs with-in the LCD TV)

RF Solutions:
Twist the TV antenna around a few degrees to acquire a stronger signal (ghost or main, digital doesn't care which one)

Alternate RF Solutions: - (Metro Areas)
Because of these poor picture or more correctly signal problems, TV stations also re-transmit their signals in the UHF TV band Ch 21 to 69. Usually from different locations in and around the city / area at lower power levels and at a different signal polarity to the main TV signal that services the area. This enables TV stations to reach areas blocked by high rise buildings or in a low lying areas. You may wish to receive both services to obtain "best" picture & sound per TV channel.


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Terminology
A polarised antenna is either "Vertically" (the long sticks go up and down) and "Horizontally" (the long sticks go side to side).

North, South refers to magnet direction usually quoted as a compass heading for pointing your TV antenna towards the TV transmitter.
Positive and Negative refer to electrical power connection and usually only quoted when a "mast head" (at antenna) or an in-line TV amplifier is used to boost the TV signal, which usually needs DC power injected into the coax (antenna lead) to work.

FM radio signals also suffer ghosting, you hear them as distorted audio, especially in a moving car on the road in the wet.

Ghosting is nothing more than the signal being received more than once, usually a micro to a millisecond later, it is the basic principle of Radar but that is another story...


73
Gary, VK3KHB


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