Recording and/or replaying teletext signals

摘要

In order to record and replay teletext signals using a VHS video recorder the teletext data is converted into a multilevel (quarternary) code at a lower (half) data rate. On record an encoder (7) takes teletext data from a RAM (6) and encodes it as a multilevel code at a lower data rate and passes it to the normal luninance processor (10) of the VCR. On playback the multilevel code is replayed and fed to a decoder (13) which converts it to binary code at the standard teletext data rate. This is stored in the RAM (6) and then read out into a teletext decoder (14) where clock run-in and framing code are added before it is combined with the CVBS in a multiplexer (15) and passed to an output 16.