Design of an automatic scan tracking system for a D-2 digital recorder

Discusses the automatic scan tracking (AST) system in a type C video tape recorder which operates over a range of -1x to +3x tape speed and has one field per scan. In a type C VTR the track pitch is 7.5 mils, and a two field (or full frame) track jump is 15 mils. The total range of the piezoelectric head has to be more than this if continuously variable tape speed is required since the relationship between the head position and tape vertical is random. This accounts for a displacement equivalent to three single field track jumps, or 22.5 mils. When designing the AMPEX VPR-300 4fsc composite digital video recorder it was important to maintain the same specification as a type C VTR, since this is now the industry standard against which new VTR's are measured, but this requires a larger dynamic range of the AST head.<>