Patent GB-774486-A (GB)
Title: Improvements in or relating to apparatus, including an electron discharge device, for magnetically recording electrical signals
IPC: H04N5/782
Filed: 1953-03-16
Abstract: 774,486. Cathode ray tubes. ARMOUR RESEARCH FOUNDATION OF ILLINOIS INSTITUTE OF TECHNOLOGY. March 16, 1953 [April 11, 1952], No. 13216/54. Divided out of 774,485. Class 39(1). [Also in Group XL(b)] In a cathode ray tube apparatus for recording electrical signals on magnetic tape the target comprises a multiplicity of wires which are sealed through the end wall of the tube and are anchored in grooves in a magnetic lamination outside the tube so as to form a plurality of recording heads, the recording heads being energised directly by current flow through the target wires produced by the electron beam instead of the recording head being shunted by the beam target wire circuit as in U.S.A. Specification 2,517,808; the tube may operate with or without secondary emission or gaseous ion flow, the video signal to be recorded can be applied to a control grid or to the target structure ; and means are provided for deflecting the primary beam over the target wires. In one form, Fig. 1, a ribbon beam is formed and focused to a crossover at 16 by curved cathode 11, electrode 12, and pairs of electrodes 13, 14 and it is refocused at the target 17 by one or two focus coils 21 and/or by wall coating 19. The slight rotation of the beam produced by coil 21 may be used to compensate slight errors in the inclination of the target wires. Two coils 24 sweep the beam horizontally. The target comprises a plate 31, Fig. 2, carrying a row of 500 tungsten wires extending parallel to the plane of the plate and bent over at their upper ends where they are sealed through the tube wall 29 and contact transducer 35. If the target is longer than the width of the tape the wires converge to the transducer which has a length equal to the width of the tape, but the target length may be equal to the latter dimension in which case the wire end portions are parallel. The wires are secured to plate 31 by glass rod 33 and insulator 33<1> and the target is secured to the tube end wall by pins 27. The transducer comprises a lamination 37 of high permeability material grooved to hold the wires 32 which are anchored at their ends by copper wedge 45. The transducer housing, which is of non magnetic material, is said to confine the magnetic fields generated by electrons flowing in the wires to a narrow region. The recording is effected line by line in synchronism with successive beam sweeps. The video signal may intensity modulate the beam or may vary the potential difference between the cathode and target wires. The tape may be initially saturated, the recording reducing the magnetisation thereof to a varying degree. a second set of wires may be provided in the grooves of lamination 37 to neutralise the D.C. component introduced by grid wires 32, and the second set, or further wires, may provide "high frequency bias." The video signal may alternatively consist of high amplitude short duration pulses. In another embodiment, Fig. 10, the beam is electrostatically or electromagnetically swept over a target comprising rod 74 carrying collector plate 72, wires 80 anchored by copper wedge 86 fitting in copper bar 84 and high permeability lamination 90 to concentrate the magnetic flux held between non magnetic conductive bars or plates 84, 85. The tape 71 is of paper or plastic coated with magnetic material. The plate 72 and wires 80 are kept at different potentials and the wires are coated with secondary emissive material. If the tube contains gas, ionisation is produced between 80 and 72 and this can be used as an alternative to secondary emission. The beam is intensity modulated with video in the conventional manner or the video is applied between grid wires 80 and target plate 72. A "high frequency bias field" is applied to the tape by an external source or may be applied between 80 and 72. It is stated that good video gradation can be obtained, even with ionisation triggering where the equivalent of a half tone print can be recorded. The target arrangement may be made by forming a helical groove and recesses 73, 83 in rod 74, inserting 72, 84, 85, 90 in the recesses, grooving 84, 90, 85 with a helical groove registering with the helical groove in the rod 74, and winding platinum grid wire in the composite helical groove so formed, sealing the assembly to the tube end wall and anchoring the wire to bar 84 by wedge 86, cutting the wire and removing the end portions below wedge 86. The target and transducer structure of Fig. 2 may be made in a similar manner. The recording gives a magnetic representation of complete visual images of a moving object, and the magnetic representation can be made visible by dusting magnetic particles on the tape. In reproduction the tape need not be scanned in the same way as during recording e.g. it may be scanned between lines or even at right angles to the recording scan direction. Adjacent lines of the magnetic image are preferably made to overlap so that it will always produce a signal, even if the playback head scans between the lines. Double interlaced scanning may be used in recording but is not preferred. If the scanning speed is reduced by a factor of three, three successive lines can be recorded in approximately the same transverse row across the tape Fig. 13 (not shown) so that each frame is made up of three transversely aligned portions. In reproduction, each frame portion could be scanned separately, but this would not be wholly satisfactory. In general, the tape can have perforations along one edge for synchronising its speed with the input signal, of a signal is derived by pick up from the magnetic recording, amplified and used to correct for phase errors. A sound track may run along one edge of the tape, Fig. 12 (not shown). Specifications 617,773 and 774,487 are referred to.