Abstract: 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.

Abstract: Standard binary teletext signals (which have a data rate exceeding the bandwidth of a standard VHS video recorder) are converted into a multilevel code so that the teletext data can be reliably recorded and replayed by a standard VHS video recorder. During recording teletext data is received at a high data rate and encoded in accordance with a multilevel code at a lower data rate and within the bandwidth of the VCR. During playback the multilevel code is decoded back into binary code at the standard teletext data rate and clock run-in and framing codes are added to provide standard teletext signal. The resulting teletext data is then combined with the video signal.

Abstract: A data decoder, for example, for decoding teletext and VPS data, comprises an input signal clamp and synchronizing signal separator circuit which receives a combined video and blanking signal and produces synchronizing pulses for a timing circuit and video signals which are applied to an ADC and a data slicer and clock regenerator (DSCR). Sliced data and clock signals feed an acquisition circuit which acquires selected data which is stored in a memory via a memory interface. A control circuit is arranged to modify the DSCR, acquisition circuit and memory interface dependence upon the type of data detected. The arrangement decoder is set to decode data of one type, for example, teletext, and if no valid teletext data is detected within a given period, for example, four television frames, the control circuit causes the decoder to attempt to decode data of the other type (VPS).