GB544614A - Improvements in and relating to remote control systems - Google Patents

Abstract

544,614. Distant control. AGA-BALTIC RADIO AKTIEBOLAG. May 22, 1940, No. 9072. [Class 40 (i)] In a system in which a transmitted frequency varies in accordance with the transmitter position and a receiver automatically moves in correspondence, the transmitter comprises means for sending signals covering at least two different frequency ranges and the receiver comprises a corresponding number of receiving units. In one arrangement, Figs. 1 and 2 (not shown), two oscillators are provided and are tuned by variable condensers driven by the transmitter, a. cam-actuated switch rendering one operative over one-half of the transmitter range and the other over the other half. At the receiver a pair of error-detector circuits of a kind known in connection with the automatic tuning of wireless receivers operate in turn to bring the tuning of the receiver into conformity with that of the transmitter with the aid of a reversible D.C. motor which at the same time drives the controlled object. In a modification, the transmitter, Fig. 3, varies the frequency of an oscillator 29 covering one range of frequencies to give a coarse reading and of two oscillators 22, 24 covering the same different range and rendered operative in turn by a cam-operated switch 18 to give a fine reading. At the moment of change-over, both oscillators 22, 24 are effective together. At the receiving end, Fig. 5, an oscillator-mixer 36 is automatically tuned with the aid of a known type of errordetector and a motor 41 to give a constant beat frequency with the frequency received from oscillator 29 and similar arrangements are provided to vary the tuning of oscillatormixers 136, 236 in accordance with the frequencies received from oscillators 22, 24. Only one of the two error-detectors associated with valves 136, 236 is effective at a time, the beat frequency in the other case being too widely different from the error-detector tuning to produce an effect. Preferably logarithmic condensers are used at both ends. To ensure that the motor 60 shall not take charge with the receiver and transmitter considerably out of step at starting it is made weaker than the motor 41 or is cut out by a differential relav while there is a substantial difference between the field currents of motor 41. Alternatively the valves 152, 153, 252, 253 may be rendered ineffective by additional grids biased from the common cathode circuits of valves 52, 53 until the latter valves are taking their maximum current.