Amplitude Shift Keying (Theory with Lab experiment)
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- Опубліковано 9 лют 2025
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• Amplitude Shift Keying...
Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In an ASK system, the binary symbol 1 is represented by transmitting a fixed-amplitude carrier wave and fixed frequency for a bit duration of T seconds. If the signal value is 1 then the carrier signal will be transmitted; otherwise, a signal value of 0 will be transmitted.
Any digital modulation scheme uses a finite number of distinct signals to represent digital data. ASK uses a finite number of amplitudes, each assigned a unique pattern of binary digits. Usually, each amplitude encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular amplitude. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the amplitude of the received signal and maps it back to the symbol it represents, thus recovering the original data. Frequency and phase of the carrier are kept constant.
Like AM, an ASK is also linear and sensitive to atmospheric noise, distortions, propagation conditions on different routes in PSTN, etc. Both ASK modulation and demodulation processes are relatively inexpensive. The ASK technique is also commonly used to transmit digital data over optical fiber. For LED transmitters, binary 1 is represented by a short pulse of light and binary 0 by the absence of light. Laser transmitters normally have a fixed "bias" current that causes the device to emit a low light level. This low level represents binary 0, while a higher-amplitude lightwave represents binary 1.
The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying (OOK), and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation),
Following are the silent features of ASK modulation.
• ASK is digital modulation technique in which carrier is analog and data to be modulated is digital. Modulated output is analog.
• Here strength or amplitude of carrier signal is varied to represent binary 1 and binary 0 data inputs; While frequency and phase of the carrier signal remain constant. Voltage levels are left to designers of the modulation system.
ASK Advantages
Following points summarizes ASK advantages:
➨It offers high bandwidth efficiency.
➨It has simple receiver design.
➨ASK modulation can be used to transmit digital data over optical fiber.
➨ASK modulation and ASK demodulation processes are comparatively inexpensive.
➨Its variant OOK is used at radio frequencies to transmit morse codes.
ASK Disadvantages
Following points summarizes ASK disadvantages:
➨It offers lower power efficiency.
➨ASK modulation is very susceptible to noise interference. This is due to the fact that noise affects the amplitude. Hence another alternative modulation technique such as BPSK which is less susceptible to error than ASK is used.
If amplitude is the only parameter of the carrier wave to be altered by the information signal, the modulating method is called amplitude-shift keying (ASK). ASK can be considered a digital version of analog amplitude modulation. In its simplest form, a burst of radio frequency is transmitted only when a binary 1 appears and is stopped when a 0 appears. In another variation, the 0 and 1 are represented in the modulated signal by a shift between two preselected amplitudes.
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