Frequency modulation

Complete Description of Frequency Modulation. A to Z information.

1. Frequency Modulation Course No.: EEE 3218 Course Title: Communication Engineering II Sessional

2. Content What is Modulation? Need of Frequency Modulation. What is Frequency Modulation ? Classification of Modulation Frequency Modulation Theory Generation of FM in Laboratory Experimental Input & Output List of Equipments Advantages & Disadvantages Applications

3. What is Modulation? Modulation is the process by which the characteristics of carrier signal is varied according to the message signal. Why is Modulation Needed? Message signal is incompatible for direct transmission. So its strength has to be increased by modulating with a high frequency carrier signal which doesn’t affect the parameters of the message signal .

4. What is Frequency Modulation? Frequency modulation is a technique by which the amplitude of carrier signal is kept constant, while its frequency is varied by the modulating signal. Classification of Modulation Amplitude Modulation Frequency Modulation Phase Modulation

5. Frequency Modulation Theory In frequency modulation, the frequency of carrier signal is varied according to the amplitude of modulating signal. Fig.: Frequency Modulation

6. Initially, when the amplitude of the modulating signal starts to increase in its positive half cycle, the frequency of the carrier signal also increases. When the modulating signal is at its peak, the modulated signal’s frequency becomes maximum. After that, when the amplitude of the modulating signal starts decreasing, a corresponding decrement in the frequency of modulated signal is noticed. At the negative peak of the modulating signal, the frequency of the modulated signal becomes minimum. Frequency Modulation Theory

7. Modulating Signal, X(t) = Em *Cos(2*pi* fm )t Carrier Signal, C(t) = Ec *Cos(2*pi*fc)t Modulated Signal, f i (t) = fc+ k f * Em *Cos(2*pi* fm )t = fc+ f* Em *Cos(2*pi* fm )t FM signal, y fm (t)= Ec *Sin( w c t +( k f Em )/ fm * Sin(2* fm *t)) y fm (t)= Ec *Sin( w c t +m f * Sin(2* fm *t)) Modulation Index, m f = ( k f Em )/ fm =(delta f/ fm ) Frequency Modulation Theory

8. Generation of FM in Laboratory FM modulator kit was used to get frequency modulated signal. Using a function generator the message signal was generated . Inside the FM modulator block, there was an option of selection of carrier signal’s frequency between 500KHz to 1500KHz. From the output of FM modulator block, we got a frequency modulated signal. The output waveshape was seen on the oscillator.

9. Fig.: Frequency Modulator Kit Fig.: Modulating Signal Fig.: Frequency Modulated Signal Experimental Input & Output Waveshapes

10. List of Components Function Generator FM Modulator Kit Power Supply (12v) Wires Oscilloscope

11. Advantages Amplitude of frequency modulated signal remains constant. Less susceptible to noise. Provide good sound quality. More efficient use of power. Disadvantages A much width channel is required. Transmitting & receiving equipments tend to be more complex.

12. Application of FM Broadcasting of FM Radio. Telemetry , Radar & Seismic Prospecting. EEG-Monitoring of Newborns. In Music Synthesis.

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