Patent GB-807594-A (GB)
Title: Improvements in and relating to magnetic recording
IPC: G11B5/008
Filed: 1957-01-03
Abstract: 807,594. Magnetic recording and reproducing apparatus. NORSK RIKSKRINGKASTING. Jan. 3, 1957 [Jan. 3, 1956], No. 359/57. Class 40 (2). A magnetic tape on which signals are stored in a plurality of longitudinal tracks has the information recorded in equal unit lengths with jumps from track to track in a recurring sequence, the successive lengths being mutually displaced by a distance less than the unit length but at least equal to the unit length divided by the number of tracks. The tape T, Fig. 2, is pressed against a cylinder C by guide rollers Q as it is moved by feed mechanism such as a capstan and pinch roller. Cylinder C, which is of non-magnetic material, is mounted together with a commutator K on a shaft G driven by a motor Mt, Fig. 5, so that the tape and the contacting part of the cylinder are moving in opposite directions as in Fig. 2, the drive of the tape and cylinder being synchronized and the circumferential speed of the cylinder being many times that of the tape (nine to one in the example). Arms radiating from the shaft G carry recording magnets M1 ... M10 together with their windings, so that the magnet gaps S1 ... S10 coincide with openings in the cylinder C, Fig. 3, which are both angularly and axially displaced relative to each other to bring each gap opposite a track on the tape. One terminal for each magnet is connected via slip-ring k0 on the commutator to a contact brush B0, while the other terminals are connected through segments k6, k7 to contact brushes B1... B10. Thus electric signals supplied in sequence through the segments energize each magnet in turn, while its gap moves through the angle Al to A2, Fig. 2. Preferably electronic means is used to bring each magnet into circuit, an amplifier tube receiving signals being provided for each magnet, the tube being controlled by pulses synchronized with the rotation of the cylinder C. These pulses may be produced electrically or electro-mechanically, photo-electrically or electro-magnetically or by means of vacuumtube generators. The cylinder C or a similar magnet cylinder may be used for reproduction from the tape T. For reproduction, to bring the recorded areas into line with the magnets, the tape and cylinder are relatively displaced, e.g. by a swinging movement of the bearings of shaft G and of the rollers Q or by a phase displacement of the shaft or the feed rollers of the tape. A stroboscopic lamp L synchronized with the signals may be used for adjustment both during recording and reproduction. To record low-frequency oscillations a separate continuous track may be provided on the tape, recording and reproduction being made by a stationary magnet Mv. Fig. 5 is a circuit diagram for recording and reproducing television signals using the stationary magnet Mv for the low frequencies. The motor Mt driving the cylinder C is connected through a phase regulator Ph to an A.C. source synchronized with the drive for the tape T and the signals. The lamp L, connected through a rectifier H to the same voltage, flashes for each revolution of the cylinder C, the regulator Ph being used to adjust the cylinder motion so that the flash always illuminates a mark on the cylinder. Picture signals are amplified by the amplifier SA and supplied to the magnets by the commutator K for recording on the tape T. The commutation of the reproduction amplifier RA is controlled by a pulse generator J which in turn is controlled by the A.C. source for the lamp L. Low-frequencies are separated out by a filter F and, after modulation by an amplifier MA, recorded by the magnet Mv. A switch N is used for the change-over from recording to reproduction, the signals picked up by the cylinder C being combined in the amplifier RA and through a corrector RK applied to an amplifier BA. A switch O changes over the magnet Mv to a demodulating amplifier AD and thence signals picked up by the magnet Mv pass through a corrector VK to the amplifier BA to unite with the signals picked up by the cylinder. By means of switch U, the lamp L, rectifier H and generator J are disconnected from the A.C. source and connected to an amplifier filter FA, so that the lamp flashes in step with the pulses picked up by the magnet Mv and the cylinder C can be adjusted by the regulator Ph as before. The generator J will then correct the commutation for the combination of the signals.