Radio Remote Control

the branch of remote control in which radio communication channels are used to transmit control commands and monitoring information (signals and measurements). The channels operate mostly in the centimeter and decimeter wavelength ranges. Radio remote-control systems can be divided into three types: radio control systems, in which a variety of command information is transmitted; radio telemetry systems, in which monitoring information is transmitted; and composite systems. Ordinary radio communication is used mainly for the monitoring and control of objects that are mobile, dispersed, and not easily accessible, such as rockets, artificial earth satellites, transportation facilities, and remote weather stations. Stationary objects, such as electric-power substations and irrigation systems, are controlled through radio-relay systems. Radio links are subject to the effects of atmospheric, industrial, and mutual (from other transmitters) radio interference, which reduces the reliability of control. For this reason, radio links are used only when wired systems are not technically feasible or economically advisable.

In radio control systems, when a command is transmitted from the operator, or controller, to the object, the code of the command entered by the operator on the control panel is converted into a sequence of electric pulses and then by means of phase, amplitude, or frequency modulation into a radio signal. In order to increase the reliability of radio control, various error-correcting codes are used. Reliability is also provided by feedback monitoring, wherein signals that confirm the reception and execution (or only the reception or only the execution) of a command are transmitted from the object to the control point. Sometimes—for example, in rocket-flight control systems—control is effected continuously by means of an error signal derived automatically from the difference between the desired and true positions of the controlled object.

In radio telemetry systems, the sensing element is a measuring transducer, or pickup. An electrical voltage proportional to the quantity being measured is produced at the output of the transducer. By means of frequency, amplitude, phase, or pulse modulation, the voltage is converted into an auxiliary signal, which is then converted by a second modulator into a high-frequency radio signal.

Since there may be as many as 10³ transducers in one radio remote-control system, a number of techniques are used to distinguish the signals produced by the transducers: frequency division of the channels according to the carrier frequencies of the auxiliary signals; time division, in which the transducers are interrogated successively; and combined frequency-time division. In composite radio remote-control systems—especially systems with digital-computer control—that involve a large number of dispersed objects, use is often made of an address (code) division of the channels. In this method, an object or a group of objects is given its own address (code) and information is received or transmitted only by objects whose address is indicated at the beginning of a transmission.