GB758865A - Improvements in and relating to the delaying of television signals - Google Patents

Abstract

758,865. Electric and magnetic recording and reproducing apparatus. BRITISH BROADCASTING CORPORATION. April 12, 1955 [April 9, 1954], No. 10565/54. Class 40(2) [Also in Group XL(b)] In apparatus for delaying television signals (see Group XL(b) ) in which the signals are recorded magnetically or electrically at a first point on a rotating drum or disc and picked up at a second point suitably displaced from the first to obtain the desired delay, variations in the amplitude of the reproduced signals due to changes in the separation of the recording and reproduction heads and the periphery of the drum or disc caused by unavoidable eccentricity are compensated by detecting the changes in separation and controlling the pick-up head spacing so as to reduce the signal variations. In one arrangement a constant amplitude signal is recorded on a separate track (or, by use of a distinguishable frequency, on a signal track) and the amplitude of this signal as picked up is detected to derive a control potential representative of the changes in ' separation. In another arrangement. where the recording medium is metallic, or in the form of a coating on a metallic backing, the detecting device comprises a small insulated metal plate facing the medium and providing an indication of the variation in spacing by the variation in capacitance between the plate and medium. The capacitance variation is employed to produce a varying control potential. Reference is also made to the use of a photo-cell with a beam of light projected through the gap between the recording head and medium. To enable the pick-up head spacing to be varied in response to the control potential, the head 26, Fig. 3, may be carried by a piezo-electric device comprising two thin rods 43, 44 of barium titanate cemented face to face. The outer faces of the assembly are sputtered with a conductive coating and electric connections to the control potential are made via a fixed support 46 and a light phosphor bronze spring 47. In an alternative arrangement (not described in detail) pneumatic means are employed comprising a piston and cylinder responsive to air pressure varied by the electric control signal. Specification 722,962 [Group XL(b)] is referred to.