Digital receiver

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DVB receiver with CI slot (right) and common interface module (bottom left)

A digital receiver (also digital decoder or digital receiver ) is a device for decoding and receiving digitally transmitted television services and related offers via cable , satellite or terrestrial antenna , especially in DVB format. Such a receiver can either be integrated directly into the playback device ( see also tuner and IDTV ) or supplement the existing equipment as a stand-alone device ( set-top box ).

Pay TV

In pay TV, digital receivers are also used in conjunction with a decoder card ( smart card ) to decrypt coded pay TV offers. In addition to a unique identifying number ( PIN ), the card contains the key that enables the decoder to decode the encrypted data stream. Known decryption methods are u. a. the systems NagraVision , Seca or Betacrypt .

radio

In addition to digital receivers for digital television , which, as in the case of DVB-S and DVB-C, can often also be used to receive radio programs , there are also those for pure audio transmissions. Corresponding formats are, for example, Digital Audio Broadcast ( DAB ) and Digital Radio Mondiale ( DRM ) and, since 2018, also for DVB-C ( see also digital radio ). As with video transmission, digital distribution enables a higher transmission quality and, thanks to compression, a larger number of stations; additional services are also possible.

Most of the time, the cost of a digital audio receiver (also called a DAB tuner box) is comparable to that of a digital radio, so that an external upgrade of an old, analog radio device is no longer worthwhile. The operation of a radio device via an additional tuner box is also quite cumbersome.

interaction

In addition to receiving, decompressing and, if necessary, deciphering the audio-video signals, digital receivers are usually also capable of processing data accompanying the program or independent data. In addition to text information services in the style of teletext ( RDS for radio), this mainly includes electronic program guides ( EPG ) and increasingly interactive services (quizzes, shopping, etc.) that require a return channel .

storage

If a viewer wants to record a program and watch any other program at the same time, he needs a so-called twin receiver with two separate tuners. Since the received digital data can be saved without loss and without great effort and then processed or archived, there are digital receivers with an integrated hard disk (so-called hard disk recorder ), DVD burners , network interfaces ( Ethernet ) or USB interfaces via which the recorded programs can be recorded can play on the PC in order to have the option of cutting them or burning them to DVD; as well as DVB reception cards (internal and external) for the PC , which, in the opinion of the media industry, provokes copyright infringements. Digital twin receivers are available with and without a hard disk. Hard disk recorders enable time-shifted television , in which a program that is currently being recorded can be played back while it is being recorded.

background

A well-known digital receiver for DVB that was widely used in Germany was the d-box 1 and its successor, the d-box 2 . The D-Box was one of the first digital decoders to be marketed by the pay TV provider DF1 / Premiere World and later by Premiere and developed by the Kirch company BetaResearch ( betacrypt encryption method , betanova Java operating system for the d-box 2 ). By packaging the program and decoder, the D-Box achieved rapid distribution and for a long time had a dominant position in the German pay-TV market.

In the course of the insolvency of the Kirch Group , BetaResearch was sold and a little later ceased development operations. In October 2003, the NagraVision encryption process replaced betacrypt .

technology

External

Despite the confusing variety of devices on the market, the technology used in the devices is fairly uniform. The Omega chipsets (STi5500, STi5518, etc.), which are leading with a market share of well over 50 percent (excluding the D-Box, which is still widely used in Germany), all contain an ST20 32-bit CPU and an MPEG decoder. For operation, you essentially only need external flash and SDRAM memory and a tuner module adapted to the respective reception technology. The STi5518 also supports the connection of a hard disk.

Integrated internally

Digital-to-analog conversion is no longer necessary for purely digital receivers . The receiver only needs a corresponding tuner module. For example, the MPEG decoding of the signal is already carried out in the commercially available tuner modules. Usually a CI interface, smart card reader and a corresponding decryption electronics module are added . In the integrated case, therefore, one no longer speaks of a digital receiver, but only of a digital tuner.

Without active antenna control

DVB-C / DVB-H / DVB-T receivers always process a static antenna signal at the antenna input, so they can only receive those programs that can be transmitted over a frequency band via a coaxial cable. It is advantageous that several such receivers can also be operated on one antenna socket without mutual interference. A disadvantage is a smaller program variety compared to an active antenna control. Some DVB-T receivers output a supply voltage at the antenna connection to supply an active indoor antenna.

With active antenna control

DVB-S / DVB-S2 receivers process more frequencies at the antenna input than can be transmitted at once via a coaxial cable (frequency range 950–2200 MHz). For this purpose, such a receiver generates special control signals (14/18 volts, 22 kHz diseqc ) at the antenna connection , by means of which it addresses the satellite frequency to be received and thus retrieves it in the upstream multiswitch or LNB , Unicable LNB .

If such devices are operated on a single-cable system (DC supply deactivated), a possible variety of programs is lost. However, the advantages of passive antenna control can then also be used. Thanks to modern digital technology, this step backwards is no longer so difficult; Thanks to compression, up to 20 TV channels (an average of 6) can now be packaged in one digital transponder. With the introduction of new compression techniques such as H.264 / Mpeg4, this will have an even more positive effect on a variety of programs. Active antenna control, indispensable for the variety of programs in the PAL era, is no longer absolutely necessary in the digital age.

Recording of digital broadcasts

Digital broadcasts can either be stored digitally directly or first converted into an analog signal and then recorded as such.

Digital recording

The recording is increasingly being carried out on a digital storage medium . A digital storage medium is connected to the receiver or a corresponding storage medium (usually a hard disk ) is already installed ( hard disk recorder ).

Analog recording

The digital systems DVB-T, DVB-S, DVB-S2 and DVB-C require special receivers or appropriately equipped television sets . The digital transmission signal is converted into an analog one in the receiver, which can be processed further by the classic analog terminal device ( tube television or video recorder). The receiver therefore works like a digital-to-analog converter.

It is particularly important to note that DVB no longer broadcasts the original VPS signal. Appropriate adjustments were only made gradually, but not all broadcasters and all digital receivers support them.

See also

Web links