Patent GB-1020422-A (GB)
Title: Improvements in or relating to magnetic recording and replay systems
Inventor: RANGER MICHAEL HARRY FREDERICK
IPC: H04N5/782
Filed: 1963-01-16
Abstract: 1,020,422. Magnetic recording &c. apparatus for video signals. THERMIONIC PRODUCTS (ELECTRONICS) Ltd. Jan. 15, 1964 [Jan. 16, 1963], No. 2051/63. Heading G5R. A transducer head for use in a magnetic recording/playback apparatus comprises a plurality of magnetic circuits assembled in stacked relation and separated from one another by non- magnetic spacing elements, each circuit including a non-magnetic gap and a magnetic switching portion normally preventing the flow of flux in the magnetic circuit, the magnetic switching portions being connected in parallel in a further magnetic circuit common thereto, and means for generating a magneto-motive force in the common circuit to cause the magnetic switching portions to switch in succession one after another from one state to another state and during such switching to permit momentarily a flow of flux in each of the plurality of magnetic circuits in succession. Magnetic heads.-Fig. 1 shows an exploded view of part of a head comprising six hundred closely spaced thin magnetic plates 1 separated from one another by insulating or non-magnetic laminations, each plate having a front polepiece 1a and a rear polepiece 1b. The plates 1 are juxtaposed with similar plates (not shown) so that the respective polepieces 1a are spaced apart to form a common non-magnetic gap extending across the front face of the head and filled by a non-magnetic shim 2. The respective rear polepieces 1b are each separated by a magnetic switching element 3 formed of a magnetic material having a " square loop " B-H characteristic. These elements 3 are assembled in ladder form between limbs 4 of permeable magnetic material provided at one end with a magnetic core 5 and a magnetizing winding 6. The elements 3 are initially all magnetized in one direction and the winding 6 is energized by a gradually increasing current in a direction to oppose the remanent magnetism in the elements 3. Successive elements 3 then change their direction of magnetization, and in changing become permeable, thereby momentarily allowing flux to flow through the magnetic circuit formed by the associated juxtaposed plates 1 so that the head scans across its width. In operation a saw-tooth wave of alternate polarities is applied to winding 6 whilst a video signal is applied to or detected from one of two windings 7 so that the head scans transverse tracks on a longitudinally moving tape. Recording and playback of video signals.-A composite video signal is separated into a D.C. restored video signal and a synchronizing signal, the former being fed direct to a winding 7 and the latter being used to generate the signal for winding 6 and also being fed to a separate recording head, Fig. 4 (not shown). Similarly on playback the synchronizing signal picked up from the tape is used to generate the signal for winding 6, Fig. 5 (not shown). The video signal passes through an amplifier, a 4À5 Mc/s. bandpass filter, an amplifier provided with A.G.C., a half-wave detector, and a further 4À5 Mc/s. bandpass filter before being added to the synchronizing signal. During recording the capstan may be driven by a 50 c.p.s. signal, and during playback the capstan may be driven by a variable frequency 50 c.p.s. oscillator controlled by a discriminator fed by the 15 Kc/s. line synchronizing signal, Figs. 7 and 8 (not shown).