8) This describes the essential skills and knowledge and their level, required for this unit. Evidence shall show that knowledge has been acquired of safe working practices and diagnosing and rectifying faults in digital television apparatus. All knowledge and skills detailed in this unit should be contextualised to current industry practices and technologies. KS01-EH179A Digital television faults Evidence shall show an understanding of digital television receivers, digital television principles and digital television faults, applying safe working practices and relevant Standards, Codes and Regulations to an extent indicated by the following aspects: T1. Integrated Receiver Decoder IRD (The Set Top Box) encompassing: sub-system components (i.e. functional blocks) and their operating parameters Basic diagnostic tests T2. Channel decoders encompassing: Method used to determining the analogue to digital converter (ADC) sampling rate. Function of the Forward Error Correction (FEC) unit and Reed Solomon (RS) and Veterbi plus interleaving. Purpose of the OFDM modulator. Principle of operation of an OFDM demodulator and hierarchical (de) modulation. Principles of operation of a QPSK demodulator. Perform measurements and diagnostic test points in a typical IRD channel decoder. T3. Conditional access encompassing: Purpose of a conditional access module (CAM). Access descrambler unit sub-system components (i.e. functional blocks) and their operating parameters Function of the component parts of conditional access descrambler unit. Purpose of a conditional access module 'smart card'. Single chip set top box sub-system components (i.e. functional blocks) and their operating parameters T4. Repair and maintenance of digital television signal decoding circuitry. encompassing: Correct operation of the transport stream processor with reference to typical input and output signal. Testing techniques to determine correct operation of the video decoder, audio decoder and PAL encoder Testing techniques to determine identify faulty data streams. Pin connections of a SCART socket. Operation of a typical UHF modulator. List precautions to be observed when performing tests on functional and non-functional units. Identify and replace faulty components in malfunctioning units. Perform functional testing after repair. T5. Describe the basic techniques used to process an analogue signal for integration in a digital broadcasting system encompassing: Basic technique of sampling an analogue waveform and assigning quantisation levels to those samples for both video and audio. Calculation of the number of pixel's per line and the sampling rate for a range of typical DTV aspect ratios. Typical sampling rates for Standard Definition Digital Television (SDTV) and High Definition Digital Television (HDTV) broadcasts. Range of different sampling structures used to sample luminance and colour difference signals. Determination of the total bit rate required for a required sampling rate. Factors limiting digital television picture quality. Minimum MPEG video requirements for HDTV and SDTV. Factors that create the need for video data compression. T6. Describe the process used to prepare video data for integration encompassing: Major methods used to compress video data. How a complete picture frame is assembled from samples, blocks, macroblocks and slices. Meaning of the terms DCT coefficients, temporal frequency, and spatial frequency, temporal and spatial redundancy. Purpose of the Discrete Cosine Transfer (DCT) processor in the processing of video data compression. Relationship between spatial frequencies, DCT coefficients and quantisation levels in the DCT block. Compression techniques used to code quantised DCT coefficients. How Run Length Coding (RLC) is used to group DCT values into a series of values. How Variable Length Coding (VLC or Huffman coding) processes each DCT value according to probability. T7. Describe the role of the DCT coder encompassing: Sub-system components (i.e. functional blocks) and their operating parameters of a DCT coder. Typical construction of a Group of Pictures (GOP). Individual frames in a GOP sequence that uses forward prediction and bi-directional prediction. Purpose of differential coding. Structure of a video Packetised Elementary Stream (PES). Types of information included in the PES. |