GB390565A - System of electrical picture transmission - Google Patents

Abstract

390,565. Television. TELEVISION LABORATORIES, Ltd., 505, Crocker Building, San Francisco, U.S.A. Nov. 30, 1931, No. 33164. Convention date, Dec. 4, 1930. [Class 40 (iii).] In television, the received picture signals are combined with impulses generated at the receiver, to form square-fronted waves, to compensate for the absence of high-frequency components in the received signals. The added impulses are preferably proportional to one or more derivatives of the received signal with respect to time, while the received signal has preferably had its high frequency components removed before transmission. The picture signals, produced at the transmitter as described in Specifications 368,309 and 368,721, are amplified at 18, Fig. 1, and fed into a low-pass filter 20 which removes the high-frequency components, before passing to the line 21. At the receiver the line 21 is shunted bv an inductance L in series with a resistance R, producing a voltage drop between the grid and the cathode of the screen-grid valve 26, thus introducing the first derivative. A similar shunt 27, 28 in the output circuit of the valve 26 introduces the second derivative and higher derivatives may be similarly added as desired. It is stated that it is necessary to introduce a derivative having a discontinuity at the instant when a picture impulse is received and that further derivatives are desirable to compensate for the effect due to the finite size of the scanning spot. Transmission may also be effected by modulating a wireless carrier wave, Fig. 7 (not shown), the received signals being amplified before the derivatives are added, Fig. 8 (not shown). An alternative shunt comprises a resistance 66, Fig. 9, in series with a condenser 67 and a resistance 68 in parallel, and if desired an inductance may be connected in series with the resistance 66, Fig. 10 (not shown). The line should have a high impedance and if necessary a resistance 22, Fig. I, or a condenser 65 may be connected in the line. Preferably the low-pass filter 20 attenuates frequencies above the highest frequency to be transmitted, proportionally to frequency. According to the Specification as open to inspection under Sect. 91, the invention is also applicable to telegraphy and the restriction of television signals to a small frequency band can allow the transmission of voice currents over the same channel. This subject-matter does not appear in the Specification as accepted.