A delayed-trigger oscillograph

The difficulty that arises in the use of a conventional oscillograph for the examination of television waveforms is in the viewing of isolated sections. If the oscillograph is used with a 50-c/s repetitive time-base, the detail of individual lines cannot be resolved, and the distinction between primary and secondary frames cannot be made, since both traces will appear superimposed. By deriving a trigger pulse from the first of the eight broad pulses in each frame-cycle and delaying this pulse by means of a variable delay circuit covering a range from 2 to 22 millisec, the variable-speed time-base of the instrument can be fired to enable either a single line or any required portion of the frame waveform to be displayed. The operating principles of the instrument are similar to those of the variable-phase oscillographs used in radar test-gear. However, since the oscillograph described has been designed for television applications, it has the advantage of deriving the required delayed time-base and marker pulse directly from the television-signal waveform.