Digital terrestrial tv

Digital terrestrial television (DTTV or DTT) is a technology for broadcast television in which land-based (terrestrial) television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format. DTTV is a major technological advance over the previous analog television, and has largely replaced analog which had been in common use since the middle of the last century. Test broadcasts began in 1998 with the changeover to DTTV (aka Analog Switchoff (ASO) or Digital Switchover (DSO)) beginning in 2006 and is now complete in many countries. The advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, satellite, and telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, and potentially lower operating costs for broadcasters (after the initial upgrade costs).

Different countries have adopted different digital broadcasting standards; the major ones are:

DTTV is transmitted using radio frequencies through terrestrial space in the same way as the former analog television systems, with the primary difference being the use of multiplex transmitters to allow reception of multiple services (TV, radio stations or data) on a single frequency (such as a UHF or VHF channel).

The amount of data that can be transmitted (and therefore the number of channels) is directly affected by channel capacity and the modulation method of the transmission.

North America uses the ATSC standard with 8VSB modulation, which has similar characteristics to the vestigial sideband modulation used for analog television. This provides considerably more immunity to interference, but is not immune to multipath distortion and also does not provide for single-frequency network operation (which is in any case not a requirement in the United States).

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