P1 - DATA TRANSMISSIONS (6)

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Digital signals

inarred 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 tv to change channel.

The switch over 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 switch over for both TV and radio means:

improved signal quality

a greater choice of programmed

being able to interact with the programme

information services such as programme guides and subtitles

optical fibres allow data to be transmitted very quickly using pulses of light

ADVANTAGES OF DIGITAL SIGNAL

before a 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

if the wave is amplified, the interference is also 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 signal to be transmitted at the same time

D - C

B - A*

B - A*

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