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Analog & Digital Communications Lab Manual, Study notes of Digital & Analog Electronics

Jaypee University of Engineering & TechnologyDigital & Analog Electronics

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MADANAPALLE INSTITUTE OF TECHNOLOGY & SCIENCE
MADANAPALLI
ANGALLU, MADANAPALLE – 517 325
ANALOG AND DIGITAL COMMUNICATIONS
LABORATORY MANUAL
DEPARTMENT
OF
ELECTRONICS & COMMUNICATION ENGINEERING
2012-13
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MADANAPALLE INSTITUTE OF TECHNOLOGY & SCIENCE

MADANAPALLI

ANGALLU, MADANAPALLE – 517 325

ANALOG AND DIGITAL COMMUNICATIONS

LABORATORY MANUAL

DEPARTMENT

OF

ELECTRONICS & COMMUNICATION ENGINEERING

MADANAPALLE INSTITUTE OF TECHNOLOGY &SCIENCE,

Department of ECE

ANALOG & DIGITAL COMMUNICATIONS

LAB MANUAL

Prepared By

Mr. P.R.RATNA RAJU.K, M.Tech, Asst. Professor Department of ECE, MITS, Madanapalle

MADANAPALLE INSTITUTE OF TECHNOLOGY AND SCIENCE,

MADANAPALLE

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

ANALOG & DIGITAL COMMUNICATIONS LABORATORY

LIST OF EXPERIMENTS

Part A (Analog Communication Lab):

  1. Amplitude Modulation and Demodulation.
  2. Frequency Modulation and Demodulation.
  3. Characteristics of Mixer.
  4. Pre-Emphasis & De-Emphasis.
  5. Pulse Amplitude Modulation and Demodulation.
  6. Pulse Width Modulation and Demodulation.
  7. Pulse Position Modulation and demodulation.
  8. Radio Receiver measurements – Sensitivity, Selectivity, & Fidelity.

Part B (Digital Communication Lab):

  1. Sampling Theorem – verification.
  2. Time division multiplexing.
  3. Pulse Code Modulation.
  4. Delta modulation.
  5. Frequency shift keying - Modulation and Demodulation.
  6. Phase shift keying - Modulation and Demodulation.
  7. Differential phase shift keying - Modulation and Demodulation.
  8. QPSK - Modulation and Demodulation. ADDITIONAL EXPERIMENTS
  9. Synchronous Detector.
  10. Differential Phase shift Keying. ADVANCED EXPERIMENTS
  11. Implementing Convolutional Encoder/Decoder using MATLAB.
  12. Implementing Viterbi Algorithm using MATLAB.

Mr. P R Ratna Raju.K & Mr. D Balakrishna Reddy Dr A.R.Reddy Faculty In-Charge Head of the Department

EXP.NO DATE Experiment Name Page No Remarks 1 2 3 4 5 6 7 8 9

Fig 3: Carrier Generator Theory: Modulation is defined as the process by which some characteristics of a carrier signal is varied in accordance with a modulating signal. The base band signal is referred to as the modulating signal and the output of the modulation process is called as the modulation signal. Amplitude modulation is defined as the process in which is the amplitude of the carrier wave is varied about a means values linearly with the base band signal. The envelope of the modulating wave has the same shape as the base band signal provided the following two requirements are satisfied (1). the carrier frequency fc must be much greater then the highest frequency components fm of the message signal m (t) i.e. fc >> fm (2) The modulation index must be less than unity. if the modulation index is greater than unity, the carrier wave becomes over modulated

Procedure:

1 Switch on the trainer and check the O/P of carrier generator on oscilloscope.

  1. Connect 1KHz with 2 Volts A.F signal at AF I/P to the modulator circuit.
  2. Connect the carrier signal at carrier I/P of modulator circuit.
  1. Observe the modulator output signal at AM O/P Spring by making necessary changes

in A.F. signal.

  1. Vary the modulating frequency and amplitude and observe the effects on the

modulated waveform.

  1. The depth of modulation can be varied using the variable knob (potentiometer)

provided at A.F. input.

  1. The percentage of modulation or modulation factor can be calculated using the

following formulas.

  1. Find the value of R from fm=1/(2PiR*C) , C=0.1μF
  2. Connect the circuit diagram as shown in Fig.2.
  3. Feed the AM wave to the demodulator circuit and observe the output
  4. Note down frequency and amplitude of the demodulated output waveform.
  5. Draw the demodulated wave form., m=

Tabular Column:

S. No Modulator O/P Demodulator O/P

Fm (Hz)

Vm (V)

Vmax (V)

Vmin (V)

m Fo (Hz)

V

(V)

PRECAUTIONS:

  1. Connect the circuit as shown in the circuit diagram.
  2. Apply the required voltages wherever needed.
  3. Do not apply stress on the components.

Result:

Fig 1: Circuit Diagram for Frequency Modulator

Fig 2 : Circuit for Frequncy Demodulator

PROCEDURE:

  1. Switch on the FM experimental board.
  2. Connect Oscilloscope to the FM O/P and observe that carrier frequency at that point

without any A.F. input.

  1. Connect around 7KHz sine wave (A.F. signal) to the input of the frequency modulator

(At AF input).

  1. Now observe the frequency modulation output on the 1st channel of on CRO and

adjust the amplitude of the AF signal to get clear frequency modulated wave form.

  1. Vary the modulating frequency (A.F Signal) and amplitude and observe the effects on

the modulated waveform.

  1. Connect the FM o/p to the FM i/p of De-modulator.
  2. Vary the potentiometer provided in the demodulator section.
  3. Observe the output at demodulation o/p on second channel of CRO.
  4. Draw the demodulated wave form

Tabular Column:

Vc= , Fc= ,Vm=

Sl No

Fm (KHz)

Tmax(μsec) Tmin(μsec) Fmax (KHZ)

Fmin (KHZ)

∆ F

(KHZ)

β B.W (KHZ)

Demod Vo (V)

PRECAUTIONS:

  1. Connect the circuit properly.
  2. Apply the required voltages wherever needed.
  3. Do not apply stress on the components.

Result:

3. Characteristics of Mixer

Aim: To observe the characteristics of a Frequency Mixer and to measure its conversion

gain..

Apparatus Required:

  1. Frequency mixer trainer kit.
  2. Function generator - (2)
  3. C R O
  4. B N C Probes

Theory: The mixer is a nonlinear device having two sets of input terminals and one set of output terminals. Mixer will have several frequencies present in its output, including the difference between the two input frequencies and other harmonic components

Circuit Diagram:

Fig 1: Mixer Circuit Diagram

PROCEDURE :

  1. Connect the circuit as shown in the circuit diagram.
  2. Apply 99 kHz signal to the base of the transistor and 100 kHz, signal to the emitter of

the transistor.

  1. Observe a sinusoidal signal with 1kHz frequency across output terminals.
  1. Vary Base signal frequency and note down O/P amplitude. The output reaches to a

maximum value at a particular frequency. Calculate conversion gain.

Conversion gain = (O/P Voltage)/ (Base signal voltage)

  1. Plot conversion gain vs base signal frequency,

Sample readings:

S.No Fx (KHz)

Fy (KHz)

Vx (V)

Vy (V)

Fo (KHz)

Output voltage(V)

Gain(dB)

PRECAUTIONS:

  1. Connect the circuit properly.
  2. Apply the required voltages wherever needed.
  3. Do not apply stress on the components.

Result:

De-Emphasis:

Procedure:

  1. Connect the circuit as per circuit diagram as shown in Fig.1.
  2. Apply the sinusoidal signal of amplitude 20mV as input signal to pre emphasis circuit.
  3. Then by increasing the input signal frequency from 500Hz to 20KHz, observe the output voltage (vo) and calculate gain (20 log (vo/vi).
  4. Plot the graph between gain Vs frequency.
  5. Repeat above steps 2 to 4 for de-emphasis circuit (shown in Fig.2). by applying the sinusoidal signal of 5V as input signal.

Sample readings:

Table1: Pre-emphasis Vi = 20mV

S.No Frequency (KHz)

Output voltage (V)

Gain (dB)

**1.

5.**

Table2: de-emphasis Vi = 5V

S.No Frequency (KHz)

Output voltage (V)

Gain (dB)

**1.

6.**

MODEL GRAPH

Result: