Digital Generation of Test Sisnals for Colour Television

A simple digital system has been developed for the generation of colour television test signals on a sample by sample basis. Essentially a minicomputer generates all sample values in a line period which are then stored and read out at four times subcarrier rate. Compared with analogue generation this approach gives higher stability, greatly increased versatility and potentially greater accuracy, depending upon the digital resolution adopted. The generator has been designed for PAL System I although the simplified approach results in slightly non-standard signals, namely, 0.36 ns error in the line period and a pseudo 25 Hz offset. However, the signals are suitable for maintenance and servicing and the generator has enabled a subjective assessment to be made of the more difficult algorithms such as those needed for colour bar transitions. Both conventional and specialised test signals have been generated, the latter being used to verify the theoretical peak subcarrier phase and gain error due to quantization.