GB1037517A - Traffic control systems - Google Patents

Abstract

1,037,517. Radio signalling; automatic gain control. RAD-O-LITE Inc. Feb. 5, 1963, No. 4636/63. Headings H3Q and H4L. [Also in Division G4] A radio transmitter for controlling traffic lights from an emergency vehicle comprises two rows of four push-buttons 2, Fig. 1 (not shown), the upper row energizing a first sub-carrier generator 6, the lower row energizing a second sub-carrier generator 8, and the four columns energizing respective ones of four tone generators feeding the sub-carrier generators. One of the buttons may also energize a relay to change the carrier from V.H.F. to H.F. Radio receivers.-The input is applied to the suppressor grid of a frequency changer 31, Fig. 2, feeding an I.F. amplifier 34, a noise limiter 66 and an I.F. amplifier 67. The load of amplifier 67 comprises circuits 68 and 69, Fig. 3, tuned to the two sub-carriers respectively and feeding respective detectors, e.g. 77, which recover the sub-carrier. Detector 77 feeds an audio detector 79 and filter 81, an audio amplifier 83 and an output stage 85 which may feed tuned relays (not shown). When one of these relays is energized a negative voltage appears on line 57 or line 58, according to which channel produced the output, and this disables the other channel, e.g. a negative voltage on line 58 cuts off valve 77. This negative voltage is also supplied to line 61 cutting off valve 59, Fig. 2, and thereby altering the cathode potential of valve 34, and a proportion of the voltage is supplied via line 53 to the suppressor of valve 34, the effect of these changes being to increase the gain of the system. A voltage proportional to sub-carrier amplitude is supplied by leads 84 and 86 to the control grids of amplifiers 34 and 67 to control the gain of the system. The control grid of valve 34 is coupled to the suppressor grid of valve 31, so that under strong signal conditions grid rectification at valve 34 produces a voltage which reduces the gain of valve 31.