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P1f: Data Transmissions
1 Digital Signals
1.1 Infrared signals carry information that allows electronic
and electrical devices to be controlled.
1.2 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.
1.3 The signal includes a start command, the instruction command,
a device code and a stop command.
1.4 The LED transmits the series of pulses. This is received by the
device and decoded to allow the television to change channel or
volume
1.5 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
2.1 Optical fibres allow data to be transmitted very quickly using
pulses of light.
3 Advantages of Digital Signals
3.1 Before an analogue signal is transmitted, it is added to a carrier
wave
3.2 The frequency of the carrier wave is
usually higher.
3.3 Interference from another wave can also be added and
transmitted
3.4 The combined wave is transmitted.
3.5 If the wave is amplified, the interference is
amplified as well.
3.6 Interference also occurs on digital signals, but is not apparent
because the digital signal only has two values.
3.7 Multiplexing allows a large number of digital signals
to be transmitted at the same time.