Aerial television

from Wikipedia, the free encyclopedia

As terrestrial television , including terrestrial television is called the television reception of a TV channel via an earth-based home antenna or an indoor antenna . The content is broadcast by the transmitter as modulated electromagnetic waves and transmitted more or less in a straight line to house or indoor antennas.

The transmission technology can be of analog or digital type. Terrestrial television was the first technology used for television broadcasting. The BBC began broadcasting in 1929, and by 1930 many radio stations had regular schedules of experimental television programs. However, these early experimental systems did not have sufficient picture quality to attract the public due to their mechanical scanning technology, and television did not become widespread until after World War II with the advent of electronic scanning technology. The television business followed the broadcast network model, with local television stations in cities and towns attached to television networks provided by either commercial (in the US) or public (in Europe) operators. Until the transition to color television in the 1950s and 60s, television programs were broadcast in black and white. There was no other method of broadcasting television until the 1950s, with the advent of cable television and community aerial television (CATV).

properties

The transmission frequencies used are in the VHF or decimeter wave range ; thus they spread - like light - almost in a straight line and can hardly follow the curvature of the earth, which severely limits the transmitter range; In addition, there are shadows from the landscape and buildings as well as weather influences. Reflections can also occur at flat obstacles in the vicinity of the receiving antenna , which superimpose the direct radiation; With analog transmission they have a disruptive effect (“ghost images”), with digital transmission, on the other hand, the transmission technology can even make use of this to increase the reception quality.

In general, a relatively large number of filler transmitters is necessary for weatherproof, area-wide reception in addition to the strong basic network transmitters (among other things for "illuminating" valleys); this technology is correspondingly expensive. Furthermore, only about 60 (the exact number may vary from country to country ) transmission frequencies are available for analog transmission , of which each basic network and filler transmitter of a larger area usually needs its own, so that no mutual interference occurs. For this reason, a maximum of just under a dozen programs with analog technology can be received at a given location. The situation is more favorable with the digital antenna television system DVB-T .

To increase the range, the transmitters are usually mounted on mountains and / or television towers or transmission masts. The television signal of a program is transmitted nationally via a radio link or via satellite. In metropolitan areas or on high mountains, the signal is then transmitted with very high power. In order to be able to supply distant areas or valleys, so-called television converters are set up, which receive the signal from a television tower, a satellite or another converter and transmit it again amplified on another channel.

Techniques used

The picture brightness signal of the analog antenna television is modulated with a variant of the amplitude modulation , the residual sideband modulation; for the color subcarrier is in PAL - and NTSC system quadrature amplitude modulation and SECAM system frequency modulation used, the sound signal is usually frequency modulated , in the CCIR system L amplitude modulated .

In 2014, digital terrestrial television will be broadcast in Europe and large parts of Asia in the DVB-T standard and the non-compatible successor standard DVB-T2 . Other, mutually incompatible digital processes are used in other regions. For example, ATSC in North America, ISDB in Japan and South America. The DTMB procedure is used in China.

Development from the 2000s

In Germany, Austria and Switzerland, as well as in many other countries, there was a switch to digital transmission of television programs in the 2000s. The broadcasting of the analogue signal was switched off regionally on a specific date and the broadcasting of the DVB-T signal was set up. In Germany, the analog broadcasting of terrestrial public television has been completely switched off since 2009, in Switzerland as early as 2008. Originally, analog antenna television should be a thing of the past throughout Europe by 2012 (see switch to DVB-T and analog switch-off ). However, this goal could not be achieved - in Moldova, digital transmission was only introduced in November 2016 (parallel to analogue).

The broadcast of the DVB-T signal was also discontinued in Switzerland in June 2019. Even German members of the Bundestag close to the border had called for the decision taken in 2018 to be reconsidered. Cable network operators in Germany had broadcast the Swiss programs legally in their networks as long as they could be received terrestrially, i.e. thanks to the so-called overspill .

There were also considerations in other countries to replace regular terrestrial television (including DVB-T) with web TV. Since the commercial introduction of DVB-T on February 23, 2003 in the Berlin area, 20%, about half only more, have been dependent on terrestrial digital television. Assuming 242 minutes of TV, 191 minutes of radio, 23 minutes of reading daily newspapers and six minutes of reading magazines, 22 minutes for books and 83 minutes of internet for every adult per day, it was calculated that web streaming would require 96 GB. Without DVB-T, there would be considerable changes in access for 1.8 million television households in Berlin, 408,000 of which use DVB-T, 264,000 of them exclusively. 182,000 households already had a broadband Internet connection, but 82,000 did not use it and around 49,000 users were unable to use it for reasons of age or money. Even if a total of 280,000 end devices are supplied by the broadband network, so the consideration, 560 Gbit / s would be necessary for web TV with 2 Mbit / s streaming. In addition, 55% of German TV programs were no longer free at the beginning of the 2010s. The use of DVB-T2, which at times required parallel operation, resulted in costs of 20 million euros annually for network operators across Germany, which ultimately had to be borne by the customer. Pressure also arose from the Federal Network Agency, which wanted to reuse the TV frequencies in the 700 MHz range (694 MHz to 790 MHz) for mobile communications.

See also

literature

  • Gregor Häberle, Heinz Häberle, Thomas Kleiber: Expertise in radio, television and radio electronics. 3rd, revised and expanded edition. Verlag Europa-Lehrmittel, Haan-Gruiten 1996, ISBN 3-8085-3263-7 .
  • Helmuth Wilhelms, Dieter Blank, Hans Mohn: Electrical specialist 3 Telecommunications. 1st edition, BG Teubner Verlag, Stuttgart, 1982, ISBN 3-519-06807-9

Web links

Individual evidence

  1. ↑ DTT debuts in Moldova. November 3, 2016, accessed March 19, 2017 .
  2. ↑ Switzerland says goodbye to digital terrestrial television , Swissinfo, June 3, 2019
  3. ^ Germans fight for their Swiss television , Swissinfo, April 23, 2019
  4. ^ Raier Bücken: Uncertain future for terrestrial television . In: VDI nachrichten: Technik & Gesellschaft, No. 29/30, July 19, 2013, p. 7