| 摘要 |
450,057. Valve modulating circuits; thermionic valves. RADIOAKT.-GES. D. S. LOEWE, 10, Wiesenweg, Steglitz, Berlin. Aug. 2, 1935, No. 21922. Convention date, Aug. 9, 1934. [Classes 39 (i) and 40 (v)] In a modulating system for impressing television signals on a carrier wave, the signals and the carrier input are applied to separate grids of the modulating valve, the output circuit of which is tuned to an harmonic of the input carrier wave. As shown in Fig. 3, the carrier source 3 is coupled to the circuit of a grid 16b, and the picture signals are applied through a choke 5 and condenser 4 to the grid 16a. The grid 16a is biassed, to preclude grid current, through a leak resistance 6 shunted by a condenser 18 which has high reactance at the picture frequency, but low resistance at the radio frequency. The grid 16b has a fixed bias which may permit grid current but is such that only positive peaks of grid potential affect the anode current, thereby enabling the anode circuit 10 to be tuned to a multiple of the frequency of the source 3. The coupling afforded by the inherent capacity 17 between the grids does not induce any substantial oscillatory voltage on the grid 16a, on account of the low reactance of the condenser 18 at the carrier frequency. In a modification shown in Fig. 3a, the grid circuits are electrostatically isolated from each other by a balancing arrangement comprising a coil 2a coupled to the coil 2 and connected to the grid 16a by a condenser 19 of about equal capacity to the inherent capacity 17. The two grids may be of the same diameter and intermeshed, or one may be of larger diameter than the other with a screen interposed. In a further modification, the carrier is applied in push-pull to the symmetrical grids 16a, 16b, the picture signals are applied to a further negative grid, and a positive screen is interposed. Specification 435,561 is referred to. |
