Pulse Amplitude Modulation And Demodulation Aim :

PULSE AMPLITUDE MODULATION AND DEMODULATION AIM : 1. To study the Pulse Amplitude Modulation and Demodulation. 2. To study the effect of variations of Sampling frequency on the demodulated output.

EQUIPMENT REQUIRED: 1. Pulse Amplitude Modulation Kit. 2. Dual Channel Oscilloscope 20 Mhz. 3. Patch chords(1set) & User Manual.

BLOCK DIAGRAM:

PROCEDURE: 1) Switch ‘ON’ the supply on the trainer kit. 2) Connect the ‘Analog Signal Output’ to ‘Analog Signal Input’ of the modulator. Adjust frequency 1 Khz. And the amplitude by the potentiometer P2to about 3Vpp.

Connect the ‘Sampling Pulse Output’ to ‘ Sampling Pulse Input’ of the modulator. Adjust the frequency of the sampling signal to 10Khz ( 10 times to AFfrequency). Connect the jumpers J12,J16 and also J13 or J14 or J15. Observe the S&H output at the output pin 6 on buffer on the oscilloscope.It is seen that during the pulse ‘ON’ time the signal is sampled (tracked) and during the ‘OFF’ period of the sampling pulse the signal is held. 7) Observe the A.F signal on one channel of the Cathode Ray Oscillscope and observe the Natural sampling output on the second channel(Pin of 3130 IC) by removing the jumper J12. 8) Observe the natural sampling output by varying the 3) 4) 5) 6)

a) Sampling frequency. b) Sampling pulse width. c) AF Signal frequency and d) AF signal amplitude. 9) Connect the J12 to get sample & hold output and repeat the Step-8. Also study the effect of the sample and hold output by connecting and disconnecting J13,J14 and J15 jumpers. 10)Now observe the flat-top sampling output at pin 15 of CD 4053. Make sure that jumper J12 connected(w.r.s to AF signal). 11)Repeat the Step-8,here also. 12)During demodulation , connect natural sampling output/ sample and hold circuit /flat top sampling output to the input of the active low pass filter. 13)This filter output is designed for 3.4Khz (cut off frequency for AF Signal Frequency) and the output of the filter is the demodulated output. 14)Study the demodulated output by repeating the step-8.

OBSERVATIONS:

1. Modulating Signal : a) Frequency= b) Amplitude= 2. Carrier Signal : a) Frequency= b) Amplitude= 3. Natural Sampling Signal : a) Frequency= b) Amplitude= 4. Sampled & Hold Waveform: a) Frequency= b) Amplitude= 5. Flat – Top Waveform: a) Frequency= b) Amplitude= 6. Demodulated Output: a) Frequency= b) Amplitude=

RESULT: The PAM modulated and demodulated waveforms are observed by varying the AF Signal frequency and the carrier Signal frequency.