We have seen that the necessary high head-scanning speed was first achieved by fast longitudinal recording techniques, then in the successful Quadruplex system by transverse scanning of the tape by a four-head drum with the video heads mounted at 90 intervals around its periphery. The transverse scan method has a lot going for it! The very high writing speed confers great bandwidth, enabling full broadcast-specification pictures to be recorded and replayed. The relatively wide tracks are almost at right angles to the tape direction so that any jitter or flutter in the tape transport has little effect on the timing of the video signal, merely causing slight momentary tracking inaccuracies, easily catered for by the wide track and the FM modulation system in use.

The cost of transverse scanning machines is high because of the need for a complex head drum system and precision vacuum tape guides. To maintain the necessary intimate contact between video head and tape, all VCRs have their head tips protruding from the surface of the drum so that they penetrate the tape and create a local spot of stretch . Hence, the need for a precise vacuum guide at the writing/reading point in a transverse machine to maintain correct tape tension. These techniques are not amenable to domestic conditions or budgets, and the alternative and simpler helical system has undergone much development. It is now used exclusively.

In a helical scan system, several problems are solved in one go,...