Patent GB-365166-A (GB)
Title: Improvements in or relating to electro-optical systems such as television or picture transmission systems
IPC: H04N11/00
Filed: 1930-10-16
Abstract: 365,166. Television. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Ives, H. E. ; 32, Laurel Place, Montclair, New Jersey, U.S.A.) Oct. 16, 1930, No. 30995. Convention date, Oct. 25, 1929. [Class 40 (iii).] Relates to colour television systems in which a plurality of primary colour light sources 171, 172, 173, Fig. 1, are controlled by picture signals whose lower-frequency and directcurrent components have been suppressed in the transmission channels B, G, R, and consists in providing means for continuously indicating or determining the amount of control of the sources 171, 172, 173 to compensate for the suppressed signal current components. The object 100 is scanned by a beam of white light passing through an apertured disc 12, and cells 40 .. 53, 40<1> .. 49<1> receive the reflected light. Those cells sensitive to e.g. green light, are connected. in parallel, and the current therefrom is amplified at 61 and 81 and transmitted over channel G; after amplification at 151, these picture signals control the source 171. Similarly the currents from the red-sensitive and blue-sensitive cells are amplified at 63, 62 and 83, 82 and control sources 173, 172. The cells 54, 55, 56 are each sensitive to one of the primary colours and are slow in action in order to emphasize the lower-frequency and directcurrent components. The respective currents are amplified at 241, and pass through milliameters 251 and low-pass filters (cut off at about 10 cycles per second) to modulators M, where they modulate a carrier current, which is transmitted over channel A to the receiver where the three colour components are separated by band-pass filters 331 and the signals amplified and rectified at 341. Alternatively a separate channel for each colour may be used. The received correcting signals preferably pass through the resistance 371, Fig. 2, to vary the bias of the last amplifier valve 151. A variable contact control 381 may be provided for manual control. Alternatively instructions for adjusting the grid bias of the amplifiers 151, 152, 153 based on current readings of instruments in the different cell circuits at the transmitter may be transmitted to the receiver over a telephone line (not shown). In this case, the dial, adjusting the grid bias, may be calibrated with the current readings given by the transmitting operator. The lower frequency components transmitted over channel A should be received in phase with the higher frequency components received from channels B, G, R and delay networks 71, 72, 73 in the channels B, G, R are preferably introduced. At the transmitter the light-sensitive cells are arranged in a cabinet 25, Fig. 4, so that cells responsive to each of the primary colours occur at the sides and in front of the object so as to prevent colour shadows. As a further precaution, the cells are behind two plates 29 of ribbed glass, the ribs crossing at right-angles. Mirrors 29 increase the amount of light falling on the cells. The object is seated at 20 and the scanning beam enters through the aperture 24. The cells are preferably electrically screened by an earthed wire mesh 27 and each cell is supported by sponge rubber. Light filters placed in front of the cells may determine to what primary colour they will respond. At the receiver mirrors 192, 193 superimpose the three colours to produce the image. The sources may be equipped with light filters 181, 182, 183. Specifications 291,370, [Class 40 (iii), Telegraphs, Electric], and 357,590 are referred to.