Subject :- Television Engineering

Topic :- High Definition Televisions

Difficulty :- Medium

• Japan had been the pioneer in developing HDTV systems. They first developed Hi-Vision (an acronym of HIgh definition teleVISION) in 1979.
• The system used 1125 lines (1035 active lines), 5:3 aspect ratio, a bandwidth of 20MHz for luminance signal and 7MHz for chrominance signal (about 4 times the bandwidth used by the traditional SDTV) and dot interleaving in addition to line interleaving.
• It was based on division of a carrier frequency into multiple frequencies and then modulating each frequency using frequency modulation and transmitting them using time division multiplexing.
• This Hi-Vision system also came to be known as MUSE (an acronym of Multiple Sub-Nyquist Encoding).
• Most of the video signal was contained in low frequencies and so it was not necessary to use the Nyquist sampling rate for the highest video frequency of 5MHz.
• Lower frequency content could be easily recovered by using low sampling rate called sub-Nyquist rate.
• So the video signal was digitized for multiplexing and recording purpose but for transmission it had to be converted back to analog signal for modulating radio frequency carriers using frequency modulation.
• Hence it was not suitable for terrestrial broadcast but was alright at that time for satellite relay systems which were capable of accommodating quite high bandwidths.
• Satellite broadcast suited Japan very well as the whole island could be covered by a single satellite.

Types of MUSE System

1. MUSE-T (Transmission) with a wider BW of 16:2 MHz.
2. MUSE-6 with a 6MHz bandwidth. This is NTSC compatible.
3. MUSE-9
4. Narrow MUSE-a 6 MHz non compatible system.