A New Teletext Channel

A new method of transmitting data suitable for a teletext service is introduced. This is a channel that is time division multiplexed into the front porch Portion of the composite video and transmits two bits of information by virtue of a burst that can assume one of four possible phases, in the preferred form. It is intended to be used together with the conventional method of teletext transmission through the vertical blanking interval to substantially reduce the waiting time for page information acquisition and display. The system is shown to have an excellent resiliency to noise. It has good potential for cost effectiveness because it uses much of the circuitry already present in a color television for detection, synchronization, and processing.