Terrestrial television
The antenna television, whether terrestrial, referred to the television receiving an earth-based TV station through a rooftop antenna or an indoor antenna. The content is provided by the broadcaster as modulated electromagnetic waves and transferred more or less straight on outdoor or indoor antennas.
The transfer of technology can be of analog or digital type.
Properties
The transmission frequencies used are in the FM or decimeter; thus they spread - like light - almost straight and can hardly follow the earth's curvature, which greatly limits the transmission ranges; added shadow effects of landscape conditions and buildings and weather conditions. To planar obstacles in the vicinity of the receiving antenna and reflections can occur, which are superimposed on the direct radiation; for analog transmission they have a disruptive effect ( " ghosting " ), in digital transmission, however, the transmission technology make this even exploited to enhance the reception quality.
In general, for a weatherproof, area-wide reception in the strong basic network channels, a relatively large number of gap-fillers necessary (including the " illumination " of valleys ); Accordingly, this technique is expensive. Further, in analog transmission only 60 transmission frequencies available, of which each base -line and gap fillers generally own a larger area is required to avoid mutual interference. Therefore, at a given location, only a maximum of nearly a dozen programs can be received with analog technology. Save it behaves in the digital antenna TV system DVB -T.
To increase the range, the stations are usually mounted on mountains and / or television towers or transmission towers. The television signal of a program is transmitted throughout the country via a microwave link or satellite there. In urban areas or on high mountains, the signal with very high power is then sent out. In order to supply more remote areas or valleys, known as television converters are set up, which receive the signal of a television tower, a satellite or a different converter and send it on another channel amplified again.
Techniques used
The brightness signal of the analog terrestrial television is a variation of the amplitude modulation of the vestigial sideband modulation, modulated; is used for the chrominance subcarrier in the PAL and NTSC systems quadrature amplitude modulation and frequency modulation is used in the SECAM system, the sound signal is usually frequency-modulated, amplitude- modulated in the CCIR system L.
Digital terrestrial television is broadcast in DVB -T system.
Current developments
In Germany, Austria and Switzerland as well as in many other countries, has been or will be converted to digital transmission of television programs. The appearance of the analog signal is at a specified day off regionally and been set up to broadcast the DVB -T signal. In Germany the analog distribution of terrestrial public service television is switched off completely since 2009. By 2012, the analog antenna TV to Europe of the past (see the switchover to DVB -T and analogue switch-off ).
On the other hand, there are considerations regular terrestrial television also to replace the DVB- T through Web TV, for example, from 2020. Since the commercial introduction of DVB- T on February 23, 2003 at the Berlin area are still 20 %, about half of only about dependent on digital TV from the transmitter. When costing 242 minutes of TV, 191 minutes of radio, 23 minutes of reading daily newspapers and six minutes in magazines, at 22 minutes and 83 minutes of Internet books every adult on the day the web streaming would require 96 GB. Without DVB- T would be eligible for the 1.8 million TV households in Berlin, of which 408,000 are using DVB- T, of which 264,000 only, significant changes in access. 182,000 households already have a broadband Internet connection, but 82,000 not use this and basically fall about 49,000 from as users because of their age or budget reasons. Even if a total of 280,000 terminals are supplied by the broadband network, 560 Gbit / s would be required for the web- TV at a 2-Mbit/s-Streaming. In addition, 55 % of German TV programs are no longer free at the beginning of the 2010s. The use of DVB -T2, which at times requires a parallel operation, arise for the network operators in Germany costs of 20 million euros, which would ultimately be borne by the customer. Pressure created by the Federal Network Agency, which wants without converting the TV frequencies in the 700 MHz band ( 694 MHz to 790 MHz) for mobile communications.