GB1041633A - Improvements in wide-band magnetic recording systems - Google Patents

Abstract

1,041,633. Magnetic recording. M. TURNER, and N. S. RUTHERFORD. June 17, 1964, Nos. 15696/63 and 24672/63. Divided out of 1.041,632. Heading G5R. In magnetically recording a television signal the part of the signal requiring the greatest resolution (i.e. near the peak white) is recorded near the remanence point of the magnetic material of the tape, and the tape is biased by a permanent magnet in the recorder so that the black level is the opposite remanence point. The synchronizing pulses are recorded in the same sense as the bias by a flux more than sufficient to saturate the tape. The ultimate limit to resolution is the spread of magnetization forwards and backwards on the tape, and this is compensated by inserting a " pre-pulse, " that is a pulse of energy having a duration too short to be recorded. An in-phase pulse is provided to compensate for spread of magnetization in one direction and an anti-phase pulse for the other. (The use of the pre-pulse is claimed in Specification 1,041,631). The Recorder (Fig. 1 and Figs. 2 to 5, not shown), using conventional “ inch wide plastic based tape 23 fed from a supply spool 17 to a take-up spool 18 around guides 19, 24, 25, 28, 30, 32, 36, biasing magnet 27 (shown disengaged), audio head 31, video head 32 and drive capstan 34. The drive is engaged by a pressure roller 35. A single motor is used. Two video tracks are laid on the edges of the tape and the audio tracks are in between the video ones. The Video head (Fig. 6 and Figs. 7, 8, 9, not shown) (which is claimed in Specification 1,041,632) has two blocks 181, 182 of non- magnetic material (e.g. copper) forming a body 183 with a face tapered to an apex 184. Thin polepieces 186, 187 are silver-soldered or glued in as shown. A thin spacer 185 of aluminium or beryllium copper between the blocks 181, 182 provides the pole gap. The coil is mounted on a magnetic core on the outer side of the polepieces (i.e. on the same side as the tape). Alternative polepiece shapes are shown. The polepiece assembly can be removed and replaced without disturbing the coil and core assembly. Circuits.-The associated circuitry is described in detail (Figs. 10, 13A, 14, not shown). Fig. 13B shows part of the recording circuit which produces the " pre-pulse." The video input signal at 300 is amplified at transistors Tr1 Tr2 whose emitter circuits include resistors shunted by capacitors to give a rising frequency characteristic. A further transistor Tr3 (of opposite polarity type to Tr1 and Tr2) has a transformer T1 connected as shown. Its inductance and distributed capacitance give it a resonant frequency of 2 to 3 Mc/s. and the circuit Q is unity. When a rapidly changing current is applied to the primary a brief pulse is developed in the secondary which is fed to the recording head. A variable D.C. bias is also applied to the recording head through resistors R7, R8.