GB588043A - Improvements in or relating to facsimile transmission systems - Google Patents

Abstract

588 , 0 4 3. Facsimile transmitters. YARBOROUGH, E. H. COOKE-. Oct. 7, 1944, No. 19285. [Class 40 (iii)] [Also in Group XXXVIII] A transmitter for enabling writing matter to be transmitted as it is executed is formed by a flexible sheet with a conducting backing stretched across another similar sheet which is rigid or rigidly supported with its conducting surface presented to the conducting surface of the other sheet. The two conducting surfaces are maintained at different electric potentials and signals are produced by pressing the upper surface into engagement with the lower surface causing currents to flow through the point of contact which set up potential differences between the ends of the sheets which are proportional to the co-ordinates of the point of contact with reference to' axes through the point at which the potential drops between each end of each sheet and the point are equal. In Fig. 1, the sheets are constituted by crossed strips 1, 2 of recording paper with metallised backings. The strip 2 is clamped directly on base 3 by end-clamps A, D and strip 1 is clamped by end-clamps B, C and extends at right angles across 2, but spaced slightly therefrom. Each end-clamp is connected through a resistance R1, R2, R3 or R4, Fig. 2, to a source of potential, the resistances connected to each strip being equal and of large value compared with the resistance of the strip. Each strip is connected to an amplifier, Fig. 3 (not shown), which is unaffected by push-push variations so as to eliminate the effect of varying contact resistance at the stylus point. The amplified voltage may be limited to avoid excessive operation of the receiver which may comprise a 'cathode-ray oscillograph or an electromagnetically operated stylus.