Patent GB-463318-A (GB)
Title: Television apparatus
IPC: H04N7/04
Filed: 1935-09-24
Abstract: 463,318. Television. HAZELTINE CORPORATION. Sept. 24, 1935, No. 26501. Convention date, Oct. 5, 1934. [Classes 40 (iii) and 40 (v)] The very low-frequency components of the vision signals are transmitted on an intermediate carrier. Successive points on a cinema film are projected on a photo-electric cell 56 with an output low-pass filter 85 with a cutoff at 800,000 cycles. The output is applied to valves 88, 90, which amplify the vision frequencies from 24 to 800,000 cycles, and to valves 94, 95, which amplify the mean-intensity frequencies from 0 to 24 cycles. The latter modulate in a valve 100 a carrier. of 800,050 cycles from a generator 17. A photo-electric cell, illuminated through the sound track on the film, is coupled to an amplifier 105, which has a cut-off at 6,000 cycles and feeds a valve 107 modulating a carrier of 807,000 cycles from a generator 21. To produce the line-synchronizing signal, a toothed wheel generator 65 on the shaft of the scanning-drum, Fig. 8 (not shown), controls a relaxation oscillator 111, 112, 113, as described in Specification 26502/35. Similarly the framing signal is derived from a generator 66. The signals are combined by feeding them through potentiometers 93, 103, 116, 117 to amplifiers 67 .. 71, which are connected in parallel to an amplifier 72 passing a band from 24 to 813,000 cycles. These frequencies modulate a carrier of very short wave length in a push-pull modulator 7. The apparatus is so designed that the modulation by the signals is positive. A Farnsworth, Fig. 10 (not shown), or an iconoscope type of transmitter may be used, Fig. 10a (not shown). Receiver. A converse system of detectors and filters is used in a superheterodyne receiver, Fig. 11 (not shown). Since the main carrier is not directly modulated by the mean intensity values, it can be used for automatic volume control. Control can also be effected from the intermediate carrier modulated by the sound. The line and frame synchronizing signals may be separated by separate amplifiers, one containing a high-pass filter with a cut-off slightly below the line frequency, and the other a low-pass filter with a similar cut-off (e.g. 2,400 cycles), Fig. 11a (not shown). The detectors and amplifiers are so arranged that the modulation of the cathoderay tube is in the correct direction, Fig. 12 (not shown). The second detector of the receiver and the vision-frequency amplifier may be combined in a single multi-stage valve, Fig. 13 (not shown). When using a push-pull amplifier 231, 232, Fig. 14, following a diode detector 229, the synchronizing peaks are applied positively to the valve 231 and negatively to the valve 232. The bias 234 for the valve 231 is highly negative, and the bias 235 for the valve 232 minimum negative, thus preventing overload by the peaks. Testing, Fig. 15 (not shown). To test the receiver, it is energized from a calibrated generator modulated by a standard vision frequency and synchronizing signals. Filter. In the band-pass filter 73.. 77, the capacities 76, 77 are the inherent capacities of the preceding valve and succeeding valve, and the values of the terminal resistances and the tuned inductance 73 are specially calculated. The filter is shielded, Fig. 16 (not shown).