Patent GB-750187-A (GB)
Title: Improvements in apparatus for the remote transmission of pictures
IPC: H04N7/00
Filed: 1953-10-27
Abstract: 750,187. Television. LABORATORIES R. DERVEAUX. Oct. 27, 1953 [Oct. 29, 1952], No. 29710/53. Class 40 (3). The synchronous scanning of the transmitter and receiver in a television system is effected by a common generator producing a scanning signal which is communicated to both camera and reproducer. Thus, as shown in Fig. 1 a transmitting station comprising camera 2, amplifier 3 and emitter 4 send image signals over channel F to a receiving station 9 with a cathode-ray tube reproducer 11, and the two stations are scanned in synchronism by means of signals from a remote generator 13 communicated over a second channel F<SP>1</SP> to scanning equipments 6 and 61 at the two stations. As an alternative to locating the generator remote from both stations it may form part of either the transmitter or receiver station. The scanning signal is in the form of a sinusoidal oscillation modulated in amplitude by a signal of the form shown at 15, 20 or 22 in Fig. 2. At the transmitting and receiving stations the signal is applied through a phase splitter, to produce 90 degrees phase-displaced waves and these waves are then applied to orthogonal deflecting systems. The resulting scanning pattern is in the form of a spiral as indicated at 19, 21 and 23 in Fig. 3 for the three modulating signals shown in Fig. 2. With a linear signal as shown at 15, the turns are equally spaced. Both the forward spiral 16 and the return spiral 16<SP>1</SP> scan a complete image and intersect a numerous points to effect a degree of interlacing. With modulating signals 20 and 22, spirals are obtained which are progressively more closely spaced at the centre and periphery respectively. By making the ratio of the sinusoidal wave frequency to the modulating frequency other than a whole number successive spiral scans are displaced angularly and the spiral form of the scan becomes masked. Since the scanning spot velocity becomes progressively greater towards the outer turns of the spiral, the image illumination in reproduction is not uniform, but may be compensated by applying the modulating signal to the cathode-ray tube grid. Alternatively, the frequency of the sinusoidal wave may be varied so as to cause the scanning spot to traverse at a constant linear speed. In addition to maintaining uniform illumination this also ensures uniform definition. Reference is made to the use of asymmetrical scanning signals. The Specification discloses four detailed embodiments, but illustrates the various circuits only in block diagram form. In the first embodiment, Fig. 4-6 (not shown), the scanning signal generator is located at the transmitter station where it controls the camera directly and also produces a signal for transmission to the receiver. A common emitter and aerial is employed for the image and scanning signal, the scanning signal being inserted in a gap in the image signal spectrum. At the receiver the scanning signal is separated out by a filter and applied through phase-splitting and amplifier stages to effect the cathode-ray tube scanning. The receiver includes also a magnetic tape recorder with two heads for recording the image and scanning signals. Reference is also made to the use of film in recording. In the second embodiment, Fig. 7-9 (not shown), the scanning signal generator is located at the receiver and is associated with an amplitude modulator, carrier frequency generator and emitter whereby it sends a signal to the transmitting station. This takes place on a channel at a frequency different from that employed for sending the image signals from the transmitter station to the receiver. The transmitter station includes a local receiver for receiving this scanning signal and applying it to scan the camera. As a further feature the receiver includes push-button means whereby a number of control signals may be sent to the transmitter station by frequency modulation of the carrier conveying the scanning signals. These signals may be employed for the remote control of camera position. The third embodiment, Figs. 10 and 11 (not shown), illustrates the application of the invention to two-colour television. At the transmitter separate cameras with optical filters are employed for the two colours and are rendered operative alternately each for the period of one spiral scan by blanking waves synchronized with the modulating signal of the sinusoidal scanning signal. Thus one colour is derived on the outward spiral and the other on the inward spiral. Two cathode-ray tubes are employed at the receiver and rendered operative alternately by similar blanking waves. Reference is made to three and four colour systems. The fourth embodiment, Figs. 12 and 13 (not shown), operates to produce stereoscopic television and is arranged in a manner similar to the two-colour system described above but with the two transmitter cameras and two receiver cathode-ray tubes associated with stereoscopic optical systems.