P1G: Data Transmission

P1G: Data Transmission

1. Information can be transmitted using analogue or digital signals.

2. ANALOGUE SIGNALS

   • Music and speech vary continuously in frequency and amplitude. In the same way, analogue signals can vary in frequency, amplitude, or both.
   • FM and AM radio = Frequency Modulated radio and Amplitude Modulated radio.
   • Noise adds extra random information to analogue signals.
     • Each time the signal is amplified, the noise is also amplified.
       • Gradually, the signal becomes less and less like the original signal.
         • Eventually, it may be impossible to make out the music in a radio broadcast against the background noise, for example.

3. DIGITAL SIGNALS

   • Digital signals are a series of pulses consisting of just two states: ON (1) or OFF (0). There are no values in between.
   • DAB radio is Digital Audio Broadcast radio - it is transmitted as digital signals.
   • Noise also adds extra random information to digital signals. However, this noise is usually lower in amplitude than the amplitude of the ON states.
     • As a result, the electronics in the amplifiers can ignore the noise and it does not get passed along.
       • This means that the quality of the signal is maintained, which is one reason why television and radio broadcasters are gradually changing from analogue to digital transmissions.

4. NOISE

   • All signals become weaker as they travel long distances, and they may also pick up random extra signals.
     • Noise is heard as crackles and hiss on radio programmes.
       • Noise may also cause an internet connection to drop or slow down, as the modem tries to compensate.

5. INFRARED

   • We cannot see infrared radiation, but we can feel it as heat energy.
     • Infrared sensors can detect heat from the body.
       • security lights
       • burglar alarms
   • Infrared radiation is also used to transmit information from place to place, including:
     • remote controls for television sets and DVD player
     • data links over short distances between computers or mobile phones

6. OPTICAL FIBRES

   • Information such as computer data and telephone calls can be converted into electrical signals.
     • These can be carried through cables, or transmitted as microwaves or radio waves. However, the information can also be converted into pulses of infrared radiation and transmitted by optical fibres.
       • can carry more information than an ordinary cable of the same thickness. They do not weaken over distance.

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