Relationship between Transmission Characteristics and Eye-pattern in Teletext System

Abstract

This report studies the relationship between the transmission characteristics and the eye-pattern in NTSC system of Teletext. 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 bitr-ate, the tolerance of the group delay characteristics of lower side needs to be set within ±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.