Patent GB-894991-A (GB)
Title: Improvements in or relating to methods of and apparatus for magnetically recording and reproducing signals
Inventor: JAMES IVANHOE JOHN PENFOUND
IPC: H04N5/7826
Filed: 1957-06-13
Abstract: 894,991. Magnetic recording processes; television. ELECTRIC & MUSICAL INDUSTRIES Ltd. June 11, 1958 [June 13, 1957], No. 18621/57. Class 40 (2). [Also in Group XL( b)] Signals arc recorded on a moving magnetisable recording medium along discrete disconnected tracks, Fig. 1, extending in the direction of movement of the medium, the tracks being spaced apart relatively to one another in a direction substantially normal to the direction of movement and the discrete tracks being progressively displaced in the direction of movement. A sequence of signals 2 formed by the discrete tracks occupy part of the length of the medium and this series of discrete tracks is then followed by further series 3, 4, &c. Apparatus for effecting the recording, Figs. 2 and 3, comprises a circular drum 5 mounted for rotation about an axis parallel to the surface of the medium 1 and at right-angles to the direction of movement, the drum carrying a series of heads 6 which are spaced apart both radially and axially so that the locus of the centres of the heads is a regular helix. The medium is maintained in proximity to a portion of the drum periphery by jockey wheels 7 and is moved continuously in either the same or the opposite direction to that of the drum periphery. A jet of air 8 may be forced between the medium and the drum to reduce head wear. The tape is held in proximity to the surface of the drum over an arc somewhat greater than the circumferential spacing of two adjacent heads. The signals to be recorded are gated into each head for a period substantially equal to the time taken for one revolution of the drum divided by the number of heads where the medium and drum periphery move in the same direction, and for a period rather less than this where the medium and drum periphery move in opposite directions. The invention is particularly applicable to the recording of television signals. The signals are gated to the heads during line blanking intervals, each track thus containing signals representing an integral number of lines except for some tracks which may contain signals representing half a line where interlaced scanning is involved. The line and frame synchronizing signals may be recorded interspersed with the video signals or may be recorded along a separate longitudinal continuous track. Where the invention is applied to the recording of colour television signals comprising a high definition signal together with two further signals of low definition, the high definition signal is recorded as described above in the tracks 2, 3, 4, &c., whilst the low definition signals are recorded between the bands of signals or in separate continuous tracks 10 along the sides of the medium. Tracks such as 10 may also be used to record accompanying sound signals and synchronizing pulses for controlling the speeds of movement of medium 1 and drum 5. For reproducing signals recorded on medium 1, apparatus (not illustrated) similar to that shown in Figs. 2 and 3 is employed, the signals picked up by the heads being gated in appropriate sequence to a common output amplifier.