Overview
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## Overview

Figure 8.1. Components of a DVB card/STB

A DVB PCI card or DVB set-top-box (STB) usually consists of the following main hardware components:

- Frontend consisting of tuner and DVB demodulator

  Here the raw signal reaches the DVB hardware from a satellite dish or antenna or directly from cable. The frontend down-converts and demodulates this signal into an MPEG transport stream (TS). In case of a satellite frontend, this includes a facility for satellite equipment control (SEC), which allows control of LNB polarization, multi feed switches or dish rotors.

- Conditional Access (CA) hardware like CI adapters and smartcard slots

  The complete TS is passed through the CA hardware. Programs to which the user has access (controlled by the smart card) are decoded in real time and re-inserted into the TS.

- Demultiplexer which filters the incoming DVB stream

  The demultiplexer splits the TS into its components like audio and video streams. Besides usually several of such audio and video streams it also contains data streams with information about the programs offered in this or other streams of the same provider.

- MPEG2 audio and video decoder

  The main targets of the demultiplexer are the MPEG2 audio and video decoders. After decoding they pass on the uncompressed audio and video to the computer screen or (through a PAL/NTSC encoder) to a TV set.

Figure 8.1, “Components of a DVB card/STB” shows a crude schematic of the control and data flow between those components.

On a DVB PCI card not all of these have to be present since some functionality can be provided by the main CPU of the PC (e.g. MPEG picture and sound decoding) or is not needed (e.g. for data-only uses like “internet over satellite”). Also not every card or STB provides conditional access hardware.

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