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Slide 1

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15th November 2010

Slide 2

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There are 2 different types of Signals
- Analogue Signals
- Digital Signals
Analogue Signals vary but digitals just on and off.
An analogue wave can take any value within a certain range
(remember analogue ­ any).
A digital signal can only take two values. These values tend to
be called on/off, or 1/0. For example, you can send data along
optical fibres as short pulses of light.…read more

Slide 3

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Digital Signals have advantages over
Both digital and analogue signals weaken as they travel, so they need to be
amplified along their route. Interference also causes random disturbances,
called noise, which can lead to a poor quality signal.
When you amplify an analogue signal, the low amplitude noise is amplified
too. So every time it's amplified, the signal loses quality.
With a digital signal, the low amplitude noise is just ignored. So the signal
remains high quality
Look at this images to see the difference when it interferes with both signals.…read more

Slide 4

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Another advantage of digital technology is that you can transmit signals at the
same time using just one cable or EM wave ­ this is called multiplexing.
Multiplexing happens in phone wires. When you're on the phone, your voice
is converted into a digital signal and transmitted regularly at very small time
intervals. In between your voice signals being transmitted, thousands of other
people's voice signals can be slotted in or multiplexed. The samples are
separated out again at the other end so the person you called can hear you ­
and only you. This happens so quickly that you don't notice it.…read more

Slide 5

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CD Players use lasers to read digital
The surface of a CD has a pattern of shallow pits to cut init it. They seem like pits
when you look from the top anyway. But the laser shines from underneath, so it
sees the pits as slightly raised areas. The areas between pits are called lands.
A laser shone onto the CD is reflected from
the shiny surface as it spins around in the player.
The beam is reflected from a land and a pit
Slightly differently ­ and this difference can be
picked up by a light sensor. These differences
In reflected signals can then be changed into an
Electrical signal.
The pits and lands themselves don't represent the digital ons and offs. Its actually
a change in the reflected beam which represents on, while no change represents
An amplifier and a loudspeaker then convert the electrical signal into sound of
the right pitch (frequency) and loudness.…read more


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