Television channel

related topics
{system, computer, user}
{city, large, area}
{law, state, case}
{group, member, jewish}
{math, number, function}
{area, part, region}
{company, market, business}

A television channel is a physical or virtual channel over which a television station or television network is distributed. For example, in North America, "channel 2" refers to the broadcast or cable band of 54 to 60 MHz, with carrier frequencies of 55.25 MHz for NTSC analog video (VSB) and 59.75 MHz for analog audio (FM), or 55.31 MHz for digital ATSC (8VSB). Channels may be shared by many different television stations or cable-distributed channels depending on the location and service provider.

Depending on the multinational bandplan for a given region, analog television channels are typically 6, 7, or 8 MHz in bandwidth, and therefore television channel frequencies vary as well. Channel numbering is also different. Digital television channels are the same for legacy reasons, however through multiplexing, each physical radio frequency (RF) channel can carry several digital subchannels. On satellites, each transponder normally carries one channel, however small, independent channels can be used on each transponder, with some loss of bandwidth due to the need for guard bands between unrelated transmissions. ISDB, used in Japan and Brazil, has a similar segmented mode.

Channel separation on over-the-air channels is accomplished by skipping at least one channel between two analog stations' frequency allocations. (There can be gaps between channels, where numbers are sequential, but frequencies are not contiguous, such as the skip from VHF low to high, and the jump to UHF.) On cable TV, it is possible to use adjacent channels only because they are all at the same power, something which could only be done over the air if the two stations were transmitted at the same power and height from the same location. For digital TV, selectivity is inherently better, therefore channels adjacent (either to analog or digital stations) can be used even in the same area.

Digital Television This basically means that before broadcasting the analogue pictures, these are transferred or coded into a very long series of zeroes and ones (or rather on/off signals) and after receiving this digital data it's decoded back to analogue pictures via a so called digital box that either is built into a TV-set, or via an external unit between the antenna and the TV.

Full article ▸

related documents
Classic (Mac OS X)
Sequential logic
Memory management
Datamax UV-1
Interrupt latency
PA-RISC family
Digital-to-analog converter
IEEE 802.2
IEEE 802.15
Time-division multiplexing
Desktop computer
Motorola 68060
Kermit (protocol)
Fibre Channel
IBM 7090
Video card
Frequency modulation synthesis
Psion Organiser
List of Macintosh models grouped by CPU type
Guru Meditation
Very high frequency
Signalling (telecommunications)
Covert listening device
Terminal emulator
Response time (technology)