GB709505A - Improvements in and relating to magnetic recording and reproducing systems - Google Patents

Abstract

709,505. Recording-apparatus. GENERAL ELECTRIC CO. July 31, 1952 [Aug. 1, 1951], No. 19402/52. Drawings to Specification. Class 106 (4). [Also in Group XXXVIII] A magnetic recording and reproducing system employs one magnetic head of the kind used for the longitudinal magnetizing method of recording and another head of the kind used for the perpendicular magnetizing method of recording, one head being employed for recording and the other for reproducing, for the purpose'of accurately reproducing undirectional voltage pulses. With a head having a magnetic gap for carrying out longitudinal magnetisation, a single unidirectional voltage pulse produces a field in the recording medium which induces in a similar type head a voltage corresponding to the intensity of the surface flux density. If the head has high electrical resistance, the said density is a minimum at the point on the record representing the peak of the pulse. The voltage output curve is thus zero at the said point and peaks of alternate polarity appear before and after said point, so that output voltage curve is different from the input voltage. With a head having a single pole piece for carrying out perpendicular magnetization, a single unidirectional pulse produces a perpendicular field in the medium having a surface flux which is of maximum density at the peak voltage of the pulse. When reproduced by a similar single pole head however, the voltage induced therein corresponds to the differential or space derivative of the surface flux and the output voltage curve is again zero at the point representing the peak of the recorded pulse, and peaks of alternate polarity again appear before and after said point. If however the perpendicularly recorded pulse is reproduced by ahead for longitudinal recording, the voltage output corresponds to the intensity of the surface flux, and an output voltage curve is obtained which closely resembles the shape of the initial recorded voltage pulse. Similarly, a pulse which is recorded by a longitudinally magnetizing head appears, when reproduced by a perpendicularly type of head, closely resembling the original voltage pulse.