Amplitude Shift Keying (ASK) Modulation and Demodulation

 

Experiment Name: 

Amplitude Shift Keying (ASK) Modulation and Demodulation

Theory

Amplitude Shift Keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In ASK, the amplitude of the carrier signal is switched between different levels in response to the digital data signal (usually a binary signal). This means that a binary '1' might be represented by a high amplitude, while a binary '0' might be represented by a low amplitude or zero amplitude. 

Mathematical Representation

The ASK signal can be represented mathematically as:

𝑠(𝑡)=𝐴⋅𝑚(𝑡)⋅cos⁡(2𝜋𝑓𝑐𝑡)

s(t)=A⋅m(t)⋅cos(2πf ct)

where:

A is the amplitude of the carrier signal’

m(t) is the modulating signal (binary data),

f c- is the frequency of the carrier signal.

Demodulation

Demodulation is the process of extracting the original information-bearing signal from the modulated carrier wave. In ASK demodulation, the received ASK signal is typically passed through a rectifier and then a low-pass filter to retrieve the original digital signal.

 

Apparatus

Signal generator

ASK modulator circuit

ASK demodulator circuit

Oscilloscope

Function generator (for generating the carrier and message signals)

Power supply

Connecting cables and probes.

Circuit Diagram:

Procedure

Modulation

Connect the signal generator to produce a binary data signal (message signal).

Set the function generator to produce a sinusoidal carrier signal at a desired frequency (e.g., 1 kHz).

Connect the binary data signal and the carrier signal to the ASK modulator circuit. Ensure the modulator circuit is powered correctly.

Connect the output of the ASK modulator circuit to the oscilloscope. Observe the modulated ASK signal on the oscilloscope. Adjust the amplitude and frequency as necessary to get a clear modulation.

Demodulation

Connect the output of the ASK modulator (the ASK signal) to the input of the ASK demodulator circuit.

Use the demodulator circuit to rectify the ASK signal, removing the negative portion of the waveform.

Pass the rectified signal through a low-pass filter to remove high-frequency components, leaving the original binary data signal.

Connect the output of the demodulator to the oscilloscope and observe the recovered binary data signal. Compare it with the original binary signal to verify the accuracy of the demodulation process.

Results

Modulated Signal:

The oscilloscope displayed a sinusoidal carrier signal whose amplitude varied according to the binary data signal. During the periods when the binary data was '1', the amplitude was at its maximum, and during '0', the amplitude was zero.

Demodulated Signal: 

The demodulated output matched the original binary data signal, confirming successful demodulation. The low-pass filter effectively removed high-frequency components, leaving a clean digital signal.

Discussion

The ASK modulation and demodulation experiment demonstrated the basic principles of amplitude modulation and its application in digital communication. The key observations included:

Effectiveness of ASK Modulation: The ASK modulation technique effectively encoded the binary data into the amplitude variations of the carrier signal. This was clearly observable on the oscilloscope.

Importance of Filtering: In the demodulation process, the use of a low-pass filter was crucial to eliminate high-frequency noise and retrieve the original binary signal accurately.

The integrity of the recovered binary signal was high, indicating that the modulation and demodulation processes did not introduce significant distortion or noise.

the experiment highlighted the fundamental aspects of ASK modulation and demodulation, providing a clear understanding of how digital data can be transmitted and received using amplitude variations of a carrier wave.