| 摘要 |
882,431. Inductive control I.F. apparatus. GENERAL MOTORS CORPORATION. Feb. 2, 1959 [Feb. 14, 1958], No. 3596/59. Addition to 843,511. Class 40(5). In a radio frequency control system and modification of that described in the parent Specification wherein a relay controls the power supplied to an apparatus in response to an actuating and a restraining voltage of opposite polarity derived respectively from an unmodulated operative signal and an unmodulated interfering signal. In the embodiment described a radio signal from a car is used to control a motor opening garage doors. A receiver comprises tuned R.F. stages T1, T2 and a detector T4, and an aerial coil 28. A control relay 2 is in the anode circuit of the second section of valve T4. A line 96 from transformer 16 provides A.G.C. When the received signal is unmodulated it is detected at grid 92 of T4. If the signal is modulated, it is detected on grid 92, and a series of pulses on line 112 is applied to grid 120 of T3, whence it is rectified by diode 156 to produce a negative voltage on line 162 which opposes the actuating voltage. The relay releases at the end of a signal, and is not operated by a modulated signal, e.g. in the form of noise. The amount of negative restraining voltage applied to line 162 in the presence of a modulated signal is determined by resistors 160 and 164, 110 and 168. The relay is not restrained by the instantaneous ambient noise produced by its own operation, by making the relay contol circuit insensitive for a short time period until such noise disappears, e.g. by fitting a back contact 6 on the relay 2. This, when opened, permits a capacitor 146 to charge, producing a positive pulse, applied to grid 18 of T4. This additional operating pulse maintains the valve conducting and the relay actuated. |
