Set Top Box – Block Diagram of DTH Receiver | New Topic

In this note, we are going to know about the Set Top Box and the Block Diagram of DTH Receiver. Welcome to Poly Notes Hub, a leading destination for engineering notes for diploma and degree engineering students.

Author Name: Arun Paul.

What is a Set Top Box (STB)?

A Set Top Box (STB) is an electrical device that uses a television and an external signal source to receive and decode digital television broadcasts. It “sits on top” of your television (thus the name) and translates digital signals into a format that it can display. STBs are often used for services such as DTH (Direct to Home), cable television, and IPTV.

There are two types of STB –

• Standard STB – It receives SD (Standard Definition) signals.
• HD/Digital STB – It supports HD content and may include features like recording, on-demand content, etc.

Block Diagram of DTH Receiver or Direct To Home System

Here is the DTH Receiver Block Diagram and explanation of each block –

• Dish Antenna: The dish antenna is a parabolic reflector that picks up electromagnetic signals transmitted by communication satellites orbiting the Earth. It is precisely positioned to point at a single satellite, allowing it to detect weak radio signals sent across long distances. The dish concentrates these signals onto a small device known as the LNB, which is located at its focal point, resulting in effective signal reception with minimum interference or loss.
• Low Noise Block Converter: The Low Noise Block Converter (LNB) is attached to the arm of the dish antenna. Its major role is to amplify and downconvert weak satellite signals acquired by the dish from a higher microwave frequency (usually in GHz) to a lower L-band frequency (950 MHz to 2150 MHz). This downconversion is required for the signals to flow efficiently through conventional coaxial cables to the interior set-top box while minimizing signal loss.
• Tuner: The tuner is the initial stage of the set-top box that processes incoming satellite signals. It selects the desired frequency channel or transponder from among the several channels delivered simultaneously. The tuner isolates and filters the selected frequency, ensuring that the demodulation process receives only the required signal, free of noise or interference from other unwanted frequencies in the L-band input.
• Demodulator: The demodulator turns the filtered signal from the tuner into a baseband digital stream by eliminating the modulation. Satellite TV signals are typically modified using techniques like QPSK (Quadrature Phase Shift Keying) or 8PSK (8 Phase Shift Keying) to increase bandwidth efficiency. The demodulator restores the original data bits, allowing the subsequent stages to segregate and decode audio, video, and control data.
• Transport Stream Demultiplexer (TS DMX): This block converts the baseband data stream into distinct audio, video, and system control streams. The transport stream is a multiplexed collection of TV channels and metadata that is commonly encoded with MPEG-TS (Transport Stream). The demux collects individual packetized streams pertaining to a specific TV channel and prepares them for decoding and display. It is necessary for channel switching and conditional access control.
• Audio & Video Decoders: The decoders decompress the extracted streams and transform them to playback formats. Video is usually compressed with MPEG-2 or MPEG-4/H.264, and audio with AAC or Dolby Digital. These decoders convert the compressed bitstreams to raw audio and video frames. This stage is in charge of presenting high-quality pictures and synchronized sound on the TV while adhering to the encoding standards employed by the broadcasting satellite service.
• Audio & Video Output: Once decoded, the final audio and visual signals are routed to the output stage. This stage includes HDMI, AV, and RF connectors that connect the set-top box to the television. HDMI delivers high-definition digital output, whereas AV or RF interfaces transmit analog signals. The output system ensures that the decoded signals match the input criteria of the connected television, allowing for correct playback with accurate timing and synchronization.
• Television (TV): The DTH setup’s final destination is the TV, which displays the decoded audio and visual signals. It receives the set-top box’s output and displays it in an easy-to-understand visual and aural manner. Depending on the TV’s capabilities, it may have features such as HD, 4K, or Dolby Audio. It enables customers to watch live broadcasts, navigate channels, use on-screen menus, and communicate with their DTH provider.