P1f: Data Transmissions_1

P1f: Data Transmissions_1

1. Digital Signals

   • Infrared signals carry information that allows electronic and electrical devices to be controlled.
   • Pressing a button on the remote control device completes the circuit. A coded signal is sent to a light emitting diode or LED at the front of the remote.
   • The signal includes a start command, the instruction command, a device code and a stop command.
   • The LED transmits the series of pulses. This is received by the device and decoded to allow the television to change channel or volume
   • The switchover from analogue to digital started in 2009 and is planned to finish by 2015. This may be delayed until more people buy digital radios. The switchover for both radio and TV means: ––improved signal quality for both picture and sound ––a greater choice of programmes ––being able to interact with the programme ––information services such as programme guides and subtitles.

2. Optical Fibres

   • Optical fibres allow data to be transmitted very quickly using pulses of light.

3. Advantages of Digital Signals

   • Before an analogue signal is transmitted, it is added to a carrier wave
   • The frequency of the carrier wave is usually higher.
   • Interference from another wave can also be added and transmitted
   • The combined wave is transmitted.
   • If the wave is amplified, the interference is amplified as well.
   • Interference also occurs on digital signals, but is not apparent because the digital signal only has two values.
   • Multiplexing allows a large number of digital signals to be transmitted at the same time.