Analog television

Analog television (or analogue television) encodes television picture and sound information as an analog signal, that is, by varying the amplitude and/or frequencies of the signal. All systems preceding digital television can be considered analog.

An analog television picture is drawn on the screen an entire frame each time, in the manner of a motion picture (cinematograph) film, irrespective of the picture content. Using NTSC (or PAL/SECAM) analog encoding and modulating onto a VHF or UHF carrier is a highly effective way of distributing an analog television picture, whereas attempting to distribute the same content in a native uncompressed digital form (as Digital Audio Compact Disc 'CD' is) would require an approx 250 G bit/s data rate, which is many times in excess of the bandwidth taken by a standard analog UHF channel.

Because there is no bandwidth compression whatsoever in analog TV, it is often a belief there are signals transmitted that are considered as carrying no useful information. However, this is partly incorrect, it has been found for example that when viewing an analog transmission, subject movement appears always to be 'natural and flowing' at all times, with a total absence of the 'jerky' unnatural movement effects seen with present-day digital TV technology (most apparent on slowly-moving subjects). This is because with analog TV there is no mechanism deciding what constitutes a 'moving object' from its 'background' and how to display movement. Each frame is refreshed in its entirety from the original source, as in the case of a motion picture cine film.

Analog television does not suffer from certain picture defects seen on present-day digital television, examples are: 1. Paint-By-Numbers color effects. (i.e. light obliquely falling onto a surface should appear smoothly-graduated, but instead appears as a series of bands, this is Quantisation Distortion due to reduced sample depth). 2. Poor Lip Sync. (Because analogue TV receives and outputs sound and video simultaneously without decompression and error correction, sync. can never be wrong). 3. StoneWall loss of reception. (Analog TV will degrade in proportion to the reduction in signal strength, however digital TV allows a significant drop in the signal strength before the picture is affected, whereupon it will completely freeze or 'block out').

Analog transmission of television will cease to operate in the United States as of February 17, 2009, making all television sets without a digital tuner unable to receive television broadcasts without an external digital broadcast receiver.

The planned transfer ("switchover") from a mixture of analogue and digital services to a completely digital service in the United Kingdom will start in 2008. Analogue transmissions will be switched off for the entire country by 2012. A nationwide campaign including the BBC and ITV is encouraging viewers to get digital television. The BBC broadcasts some programmes of its digital television channels on their analogue channels. London will be hosting the Olympic Games in 2012 so all British coverage of the games will be in digital.

Japan is also running an intense nationwide campaign announcing the planned switchover to digital on July 24, 2011. Many television stations around the country are already broadcasting simultaneously in digital, or are planning to start digital broadcasts by 2007.

A report has predicted that in 2007 Finland will become the first country to fully switch off its analogue signals.[1]

Common analog television systems:
* NTSC
* PAL
* SECAM
* Slow-scan television
* Narrow-bandwidth television

See also

* Broadcast television system
* Terrestrial television

External links

* Conventional Analog Television - An Introduction