02 frequency modulation and demodulation, Study notes of Digital & Analog Electronics

Download 02 frequency modulation and demodulation and more Study notes Digital & Analog Electronics in PDF only on Docsity! EXPERIMENT NUMBER 2 Frequency Modulation & Demodulation AIM: To perform frequency modulation and demodulation and for various modulating voltages and plot the relevant waveforms. EQUIPMENT REQUIRED COMPONENTS REQUIRED 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 than 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. Connections are made as shown in the circuit diagram; only potentiometer is not connected initially. 2. Another end of 1K resistor is grounded and Vcc is set to +12V. 3. Output is observed on the display which is the carrier signal generated by the IC. 4. Note down the carrier sine wave frequency fc of the IC. 5. Now connect the potentiometer and apply the modulating signal m(t) with suitable amplitude to get undistorted FM signal. DESIGN PROCEDURE Design 1: 1. FM Modulator Circuit Let carrier frequency fc = 3 KHz, fc = 0.3/RCt Choose R = 10KΩ=Ra= Rb, then Ct = 0.01μf Take RL = 10KΩ, CC = 0.01μf 2. Demodulator using PLL Let fo = fc = 3KHz, fo = 1.2/4R1C1 Choose C1 = 0.01μf, then R1 =100 KΩ Filter Design: Let fm = 1 KHz = 1/2πRC Choose C = 0.1μf, then R = 1.59 KΩ Design 2: 1. FM Modulator Circuit Let carrier frequency fc = 5 KHz Choose R = 10KΩ=Ra= Rb, then Ct = 0.001μf Take RL = 10KΩ, CC = 0.01μf 2. Demodulator using PLL Let fo = fc = 3KHz, fo = 1.2/4R1C1 Choose C1 = 0.001μf, then R1 =100 KΩ Filter Design: Let fm = 1 KHz = 1/2πRC Choose C = 0.1μf, then R = 1.59 KΩ CIRCUIT DIAGRAM