“Telecommunications” means communication at a distance and includes radio and television, mobile telephony, telemetry, and so on. The information to be transmitted must cause modulation of a high-frequency carrier. In amplitude-modulation (AM), the amplitude of a high-frequency carrier is varied in response to a low-frequency signal. A recent paper described a laboratory experiment for learning the principles of radio.1 The experiment described below demonstrates the telemetry of measurement data. The telemetry system includes a laser or a light-emitting diode with a light guide and is used for remote temperature measurements.