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Amplitude shift keying
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- 2. Introduction Digital data, morespecifically, the binary data changes the properties of the carrier signal • Amplitude • Frequency • Phase
- 3. Digital modulation • Indigital modulation, an analog carrier signal is modulated by a discrete signal Changing amplitude, frequency or phase in proportional to the binary data, produces digital modulated signal called • Amplitude Shift Keying (ASK) • Frequency Shift Keying (FSK) • Phase Shift Keying (PSK)
- 4. ASK – Amplitudeshift keying • Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. • The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant. • The level of amplitude can be used to represent binary logic 0s and 1s.
- 5. Binary ASK(BASK) orOn-Off Keying (OOK) • Although we can have several levels (kinds) of signal elements, each with a different amplitude, ASK is normally implemented using only two levels. This is referred to as binary amplitude shift keying. • We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ON keying operation and hence the name given OOK.
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- 7. MSK – Multipleshift keying • The above discussion uses only two amplitude levels. We can have multilevel ASK in which there are more than two levels. We can use 4,8, 16, or more different amplitudes for the signal and modulate the data using 2, 3, 4, or more bits at a time.
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- 9. Demodulator Or Detector •The demodulator determines the amplitude of the received signal and maps it back to the symbol it represents, thus recovering the original data.
- 10. Pros and Cons Pros: •ASK transmitter and receiver are simple to design. • ASK needs less bandwidth than FSK. Cons: • ASK transmission can be easily corrupted by noise Application: • early telephone modem(AFSK) • ASK is used to transmit digital data over optical fibre.