Telecommand

A telecommand is a command sent to control a remote system or systems not directly connected (e.g. via wires) to the place from which the telecommand is sent. The word is derived from tele = remote (Greek), and command = to entrust/order (Latin). Systems that need remote measurement and reporting of information of interest to the system designer or operator require the counterpart of telecommand, telemetry.

Examples

• Control of a TV from the sofa
• Remote guidance of weapons or missiles
• Control of a satellite from a ground station
• Flying a radio-controlled airplane

Transmission of commands

For a Telecommand (TC) to be effective, it must be compiled into a pre-arranged format (which may follow a standard structure), modulated onto a carrier wave which is then transmitted with adequate power to the remote system. The remote system will then demodulate the digital signal from the carrier, decode the TC, and execute it. Transmission of the carrier wave can be by ultrasound, infra-red or other electromagnetic means.

New Applications

Often the smaller new remote controlled airplanes and helicopters are incorrectly advertised as radio controlled devices (see Radio control) but they are either controlled via infra-red transmission or electromagnetically guided. Both of these systems are part of the telecommand area.

Encryption

To prevent unauthorised access to the remote system, TC encryption may be employed. Secret sharing may be used.

See also

• Radio control
• Teleoperation
• Telerobotics
• Telemetry
• Aeromodelism