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

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

), 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

Telemetry

Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...

.

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

Radio control

Radio control is the use of radio signals to remotely control a device. The term is used frequently to refer to the control of model vehicles from a hand-held radio transmitter...

) 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

Encryption

In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...

 may be employed. Secret sharing

Secret sharing

Secret sharing refers to method for distributing a secret amongst a group of participants, each of whom is allocated a share of the secret. The secret can be reconstructed only when a sufficient number of shares are combined together; individual shares are of no use on their own.More formally, in a...

 may be used.

See also

• Radio control
  Radio control
  Radio control is the use of radio signals to remotely control a device. The term is used frequently to refer to the control of model vehicles from a hand-held radio transmitter...
  
  
• Teleoperation
  Teleoperation
  Teleoperation indicates operation of a machine at a distance. It is similar in meaning to the phrase "remote control" but is usually encountered in research, academic and technical environments...
  
  
• Telerobotics
  Telerobotics
  Telerobotics is the area of robotics concerned with the control of robots from a distance, chiefly using wireless connections , "tethered" connections, or the Internet...
  
  
• Telemetry
  Telemetry
  Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
  
  
• Aeromodelism