Amplitude shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. It imparts discrete amplitude levels to a sinusoidal carrier signal. ASK can be binary, using two amplitude levels, or multilevel using more than two levels. The modulation is performed by band-limiting the signal to round off sharp discontinuities before transmission. Demodulation recovers the band-limited bit stream and regenerates the binary bit stream. ASK is commonly used to transmit digital data over optical fiber and transmit Morse code using LED transmitters.

1. AMPLITUDE SHIFT KEYING

2. A form of amplitude modulation process.
Represents digital data as variations in the amplitude of a carrier wave.
Imparts to a sinusoid, two or more discrete amplitude levels.
Uses a finite number of amplitudes, each assigned a unique pattern
of binary digits.
What is Amplitude Shift Keying ?

3. A Simple ASK Wave

4. ASK GENERATION AND MODULATION
From a sinusoidal wave signal, ASK output is generated by BAND LIMITING method.
By applying BAND LIMITING method, sharp discontinuities would be rounded-off,
before transmission.

5. Conversion Of Original Message To ASK Through
Band Limit Method

6. Amplitude Shift Keying is of Two types-
1. Binary ASK
2. Multilevel ASK
Binary ASK is implemented using only 2 levels.
It is known as ON-OFF keying.
Multilevel ASK is implemented with more than two level.
Different Amplitude used are – 4,8,16…
Different Bits used are- 2,3,4…
TYPES OF AMPLITUDE SHIFT KEYING

7. Binary amplitude shift keying

8. DEMODULATION process consists of two stages-
 Recovery of band limited bit stream.
 Regeneration of binary bit stream.
DEMODULATION

9. ASK SYSTEM DIVISION
ASK System
Transmitter
Linear model of
effects of
channel
Reciever

10. IN OUR DAILY USE
 Commonly used to transmit digital data
over optical fibre.
 Transmit Morse code.
For example, in LED transmitter.

11. Frequency Division
Multiplexing

12. FDM
 Sharing is done by assigning each user a specific
frequency (Carrier Frequency)
 Modulation equipment is used to move each
signal to the required frequency band.
 Multiplexing equipment is needed to combine
the modulated signal

13. FDM
 Separation of spectrum into smaller frequency
bands
 Channel gets band of the spectrum for the whole
time

14. User 1
User 2
User 3
M
O
D
U
L
A
T
O
R
f1
f2
f3

15. All the users transmit their data simultaneously….
f1 f2 f3

16. The Received data at the Receiver
f1 f2 f3
f1 f2 f3
The Filter
The output
f1 f2 f3

17. FDM process

18. FDM process

19. Advantages
no dynamic coordination
needed
works also for analog signals

20. Twisted Pair Cable
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21. Introduction
• Twisted pair is the simples, oldest and low priced cable
medium.
• It is made up of two insulated copper wires, typically, twisted
around each other in a continuous spiral.
• The purpose of twisting the wires is to reduce electrical
interference (or noise) from similar pairs close by.
Unshielded Twisted Pair (UTP) Cable
– Shielded Twisted Pair (STP) Cable
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22. Twisted Pair Cable
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23. Unshielded Twisted Pair (UTP) Cable
• Unshielded Twisted Pair (UTP) is the most common type of twisted
pair cable used in telecommunication networks.
• The reason for placing twist in the pair of wires is to minimize the
vulnerability of the twisted pair cable to external electrical noise.
• Its frequency range is suitable for data transmission as well as voice
transmission (100 Hz-5 MHz).
•
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25. UTP Cable
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26. Advantages
• The advantages of UTP are its low cost,
• It is easy to installation procedure.
• It is basically used in LAN implementations.
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27. UTP color codes
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28. Shielded Twisted Pair (STP) Cable
• In Shielded Twisted Pair cable, each pair of
insulated conductors is encased in a metal shield
to prevent Crosstalk.
• The quality aspect of shielded twisted pair is
same as the unshielded twisted pair but the
shield must be connected to ground.
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30. STP Cable
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31. Uses
• STP cables use same connectors as UTP, and are
more expensive than UTP cable.
• It is used for both analog and digital
transmission.
• It is said to be a “balanced transmission medium
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