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Experiments

PURPOSE:

The main objective of this experiment is to get the knowledge about working and functioning of the PSK modulator and demodulator. PSK is basically a digital modulation technique in which the digital data is transferred from one user to another user by changing the phase of a carrier signal. The modulation occurs by varying the sine and cosine inputs at a precise time. PSK uses a finite number of phases each assigned a unique pattern of binary digits. Each phase encodes an equal number of bits. Hence, the output waveform of the modulator is the shift in phase of the signal on the basis of the input signal. The demodulator, which is designed specifically for finding the phase of the received signal and maps it back to the original data. This requires the receiver to be able to compare the phase of the received signal to a carrier signal.

The advanced technique of PSK is known as QPSK, which is much similar to the PSK except that in PSK there are only two angular phase shifts taken for representing the signal, but in QPSK there is more than two angular phase shift is present. The modulation and demodulation of the QPSK are done with four-bit binary data. This technique is used to double the binary data rate of the information signal. It is widely used for wireless communication.

 

INFRASTRUCTURE:

For this purpose, the connecting wires, CRO, function generator and the modulator and demodulator kits of the above said experiments are used.

Modulation and Demodulation Kit

Output Wave Forms:

USP:

This experiment helps the students to understand the concept of modulation and demodulation process of the digital data/voice transmission/reception techniques.

PURPOSE:

The main objective of this experiment is to get the knowledge about working and functioning of the PAM/PWM/PPM modulator & Demodulator. It is the process in which the parameters of the pulse train are varied in accordance with the instantaneous value of the modulating signal. In Pulse Modulation system, modulating signal is continuous signal while the carrier is not a continuous signal but consist of a pulse train. Also, the signal is sampled at regular intervals & each sample is made proportional to the amplitude of the signal at the instant of sampling. It is the simplest form of Pulse Modulation. The PAM is not popularly used since pulses are not of constant amplitude. The practical form of PAM is referred to as natural PAM because the top of the pulses follows the shape of the modulating signal. The pulse train acts as a periodic switching signal to the modulator, which when switched ON allows samples of the modulating signal to pass through to the output. Because of its wideband nature, PAM has a very restricted range of application for direct transmission of signals. It is used in instrumentation system & Analog to Digital convectors used for computer interfacing.
Also, this experiment contains modulation and demodulation of the PWM. It is the process in which the width of the carrier pulse is made to vary in accordance with the instantaneous value of the sampled modulating signal. It is also known as pulse duration modulation. In this system, amplitude & starting time of each pulse is fixed but the width of each pulse is made proportional to the amplitude of sampled message signal at that instant. In PWM, OFF time is constant but all the variations occur in the “ON” time and the average “ON” time is constant.
PPM is also similar to the above experiments. It is the process in which the position of the carrier pulse is made to vary in accordance with the instantaneous value of the sampled modulating signal. In this system, amplitude & starting time of each pulse is fixed but the position of each pulse is made proportional to the amplitude of sampled message signal at that instant.
INFRASTRUCTURE:

For this purpose, the connecting wires, CRO, function generator and the modulator and demodulator kits of the above said experiments are used.

PAM Modulator and Demodulator Kits

PAM/PWM/PPM Modulator and Demodulator Kits

 

USP:

This experiment helps the students to understand the concept of modulation and demodulation process when the carrier signal is in the form of a pulse. The carrier signal is basically the other signal of high frequency and amplitude, in general method the carrier signal signs and cosign signal. So this experiment focuses on how the modulation and demodulation are done when the carrier signal is changed.

PURPOSE:
The main objective of this experiment is to get the knowledge about working and functioning of the ASK, FSK modulator and demodulator. Amplitude shift keying (ASK) is a relatively new system in which carrier may be shifted between two amplitude levels depending upon the levels of the digital input signal 0 or 1.In digital communications, the modulating signal consists of binary data. This data is used to modulate a carrier wave with a fixed frequency. Input data may represent the digital computer outputs or PCM waves generated by digitizing voice or video signals. This modulation process involves switching or keying the amplitude or frequency of the carrier in accordance with the input data. Thus amplitude Shift keying (ASK), Frequency Shift Keying (FSK) can be viewed as special cases of AM& FM respectively. ASK or ON-OFF keying (ASK) is the simplest digital modulation technique. The simplest method of modulating a carrier with a data stream is to change the amplitude of the carrier wave every time the data changes. This modulation technique is known as ASK. The simplest ways of achieving ASK is by switching ON the carrier whenever the data bit is a 1 & switching OFF when the data bit is a 0.

 

Similarly, in FSK, the carrier frequency is shifted in accordance with the digital modulation signal. If the higher frequency is used to represent a data 1 & lower frequency to represent data 0, the resulting FSK waveform is obtained. In FSK modulation technique, the modulated output shifts between two frequencies for all 1 to 0 transitions. The carrier frequency for FSK modulation is greater than twice the modulating frequency. The FSK modulator is built around the 2 to 1 multiplexer which switches between the two signals for all 1 to 0 transitions. FSK demodulator employs phase locked loop logic for the recovery of data. The digital PLL forms the heart of this logic. The PLL centre frequency & lock range are fixed. Thus the phase detector output at the PLL directly gives the detected data.

INFRASTRUCTURE:

For this purpose, the connecting wires, CRO, function generator and the modulator and demodulator kits of the above said experiments are used.

ASK Modulator and Demodulator Kits

Output WaveForm:

FSK Modulator and Demodulator Kits:

USP:

This experiment helps the students to understand the concept of ASK/FSK modulation and demodulation process. In ASK only the amplitude of the carrier signal changes while the other components remain unchanged. In FSK the frequency of the carrier signal is changed while the other components remain unchanged. So the main focus of this experiment is to differentiate, how the signal is transmitted when the amplitude/frequency of carrier signal changes.