Patent GB-377169-A (GB)
Title: Improvements in or relating to picture telegraph, television and like systems
IPC: H04N7/06
Filed: 1931-01-14
Abstract: 377,169. Television. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE, 12, Hallesches Ufer, Berlin. Jan. 14, 1931, No. 1327. Convention date, Jan. 21, 1930. Void [Published under Sect. 91 of the Acts]. [Class 40 (iii).] Each point of a picture is given a characteristic frequency, currents varying in amplitude in accordance with the brightness of the picture points being transmitted simultaneously for all the points of the picture. Transmitter. Light from a source L, Fig. 1, passes through discs S1, S2, and falls on the object Z from which it is reflected on to the light-sensitive cell. The discs S1, S2 each have a series of concentric zones adapted to interrupt the light at different frequencies. Thus the disc S1 illuminates the object in horizontal zones of frequencies of interruption from 201,000 to 300,000, Fig. 3a, while the disc S2 illuminates the object in corresponding vertical zones, Fig. 3b, so that each elemental area of the object has a characteristic frequency formed by the beat frequency of the two interrupted beams falling on it, Fig. 3c. The discs S1, S2 may be apertured, and to prevent the lines of illumination, Fig. 3, being curved, perforated strips may replace the discs or the projection may be optically distorted to compensate the curvature of the zones. The object may be illuminated and an image projected on to the discs, the cell receiving light passing through the discs. Transmission. Two or more transmitters may be employed, or a single transmitter is modulated by a number of auxiliary frequencies each of which is modulated with a part of the frequency band to be transmitted. Receiver. A block of material capable of oscillation is divided into columns 1 .. 4 .., Fig. 4, which have natural frequencies equal to the characteristic frequencies at corresponding points of the picture of Fig. 3c. This block is mounted on a quartz crystal Q, Fig. 5, to which are applied the frequencies obtained by demodulation of the transmitted energy. A block Y of lead damps the oscillations and prevents the formation of standing waves. Each column thus vibrates with an amplitude corresponding to the brightness of the associated picture point. Light from a source L is reflected from the columns to a screen S, which is painted black at the points illuminated when the columns are at rest, so that the vibrations of the columns illuminate unpainted portions of the screen in accordance with their amplitudes. An opaque grid may replace the painting on the screen. Longitudinal vibrations of the columns may also be utilized, as by setting up a current of air which opens an elemental screen to disclose an elemental light source. The columns may be of quartz and enclosed in a glass case at low pressure with an electrode at the base and a perforated electrode at the top, On applying the received signals to the electrodes, the quartz columns vibrate and the glow phenomenon may be viewed through the perforated electrode. Where the columns have natural frequencies differing from those associated with each picture point at the transmitter, a new carrier wave may be added at the receiver whose " frequency is regulated so that the received picture is placed in the right location in the picture plane." The columns may be arranged in straight lines or in arcs, and magnetic and electrical methods may be used to set the columns in vibration. The image produced at the receiver may be scanned and transmitted in the normal manner in those cases where the object is too poorly illuminated to allow of scanning by the usual method and it is stated that an optical image need not be produced but that the electric or magnetic fields released from the receiver may be scanned with a search coil.