oded for transmission in 9 bit words signals, since the effects on the separate paths of the interconnec- in a specified form, set out in a detailed encoding table. The least 57/14 Video transmission can be transmitted through a 36MHz transponder. If necessary, for Table 57.5 CCITT Recommendation 656 table contact satellite distribution to cable networks, it is possible that four assignments programmes at 15Mbit/s of NTSC/525 can be transmitted through Contact Signal line Contact Signal line a single transponder, although picture quality will be significantly degraded unless sophisticated bit-reduction systems are used. Clock A Clock B Where the highest quality digital transmission of CCIR Recom- System ground System ground mendation 601 (4:2:2) digital signals is required, 140Mbit/s (or more precisely 139.264Mbit/s) represents the European standard Data 7A(MSB) Data 7B fourth order digital transmission level chosen to provide 30 X 4 Data 6A Data 6B X 4 = 1920 telephone channels each of 64kbit/s, after taking into account the necessary housekeeping overheads incurred at each Data 5A Data 5B multiplexing stage. Data 4A Data 4B For a typical 140Mbit/s system, 5Mbit/s are allotted for audio, Data 3A Data 3B asynchronous multiplexing and other system housekeeping, leaving about 134Mbit/s for the coded video signal. Removal of the line Data 2A Data 2B blanking periods from 4:2:2 digital component video results in Data 1A Data 1B 175.5Mbit/s representing the active line periods. This provides a theoretical bit rate reduction of 18% at the cost of some buffer Data OA Data OB storage and digital line sync data. A further 8% reduction could be Spare A-A Spare A-B achieved by the removal of the field blanking intervals, although Spare B-A Spare B-B this would require significantly more buffer storage. With about 134Mbit/s available for digital video, the effective average data Cable shield word length must still be reduced from its initial 8 bits to an average of not more than 6.11 bits. There are a number of ways in which