RELATIONSHIP BETWEEN TRANSMISSION CHARACTERISTICS AND EYE-PATTERN IN TELETEXT SYSTEM.

The relationship between the transmission characteristics and the eye-pattern in NTSC system of Teletext is studied. The computer analysis is adopted to this study by using the method of the eye-pattern simulation. In this report, the eye-height is evaluated by the value of the sampling clock point linked with the clock-run-in signal. The results indicate that the eye-height is more dependent on the group delay characteristics than on the amplitude characteristics, and the optimum bit-rate is effected by the group delay characteristics of the lower side of the pass-band, for example, in case of 5. 7 Mb/s bit-rate, the tolerance of the group delay characteristics of lower side needs to be set within plus or minus 100 ns. In conclusion, an improvement of the group delay characteristics both on the transmitter and the receiver is one of the key factors for better quality of Teletext System.