The document discusses frequency modulation (FM) in data transmission. It defines key terms like frequency, modulation, data, and transmission. It describes different types of modulation including FM and how it differs from amplitude modulation. It discusses narrowband and wideband FM, how to generate FM signals both indirectly using an integrator and directly using a voltage-controlled oscillator. It also covers FM demodulation using frequency discrimination and phase-locked loops. Finally, it provides details on stereo FM transmission, including how the left and right signals are combined for compatibility with mono receivers.

1. FREQUENCY MODULATION IN DATA TRANSMISSION

2. PRESENTED ON THE BASIS OF TECHNICAL REPORT BY : RAJIB MODAK BISWAJIT MONDAL & PRANAB KUMAR BANDYOPADHYAY

3. What is FREQUENCY ?? What is MODULATION ?? What is DATA ?? What is TRANSMISSION ??

4. Modulation Pulse Wave Modulation Continuous Wave Modulation Amplitude Modulation Linear Modulation Non-linear Modulation Frequency Modulation Phase Modulation

5. What is Frequency Modulation ?? Carrier Signal Baseband Signal Modulated Signal

6. There is two types of Frequency Modulation with respect to bandwidth:--- i> Wide Band Frequency Modulation ii> Narrow Band Frequency Modulation

7. GENARATION OF NARROW-BAND FM SIGNAL : e (t) _ NBFM Integrator m Product Modulator ∑ + Accos(2Πfct) Phase Shifter Narrow – Band Phase Modulator

8. Bandwidth Of FM: Theoretically the Bandwidth Of FM is infinite (for Sinusoidal Modulation). But practically FM wave is effectively limited to a number of significant side frequencies (almost 200 kHz). From Carson’s rule approximation Bandwidth of FM - - BT 2 f + 2fm = BT 2 f (1 + 1/β) =

10. Difference Between AM & FM : 1> In case of AM instantaneous phase contains baseband Signal. But in case of FM that contains baseband as well as higher order odd harmonics. AM signal is amplitude modulated , but FM is amplitude As well as frequency modulated. 2> 3> The bandwidth of FM wave is much larger than AM wave.

11. How we create FM Signal ? i>Indirect Method ii>Direct Method

12. Indirect Method of FM Generation :----- Integrator Narrowband Phase Modulator Frequency Multiplier Base Band Signal FM Signal Crystal Oscillator

13. Indirect Method to Generate WBFM for Practical use:- Integrator Narrow Band Phase Modulator Frequency Multiplier (*100) Frequency Multiplier (*75) Mixer FM signal Baseband signal fc=100MHz Δf=75KHz f1 =0.1 MHz f2 =8.5 MHz Crystal Oscillator Crystal Oscillator

14. DirectMethod of FM generation:---- VCO Frequency Multiplier Mixer Frequency Multiplier Bandpass Filter WBFM Base band Signal Fixed Oscillator DISADVANTAGE: very poor frequency stability due to unstable basic oscillator unlike crystal oscillator.

15. Feedback Scheme For Frequency Stabilization of a Direct Frequency Modulator:- VCO Base Band Signal Frequency stabilized FM wave LPF & Amplifier Frequency Discriminator Mixer Crystal Oscillator

16. Demodulation of Frequency Modulated Wave:- Frequency Demodulation is the process that enables us to extract the original modulating signal. There are two basic methods for demodulating the FM waves: Based on Frequency Discrimination Based on Phase Locked Loop

17. Frequency discriminator:- A frequency discriminator is an FM demodulator which must produce an output voltage linearly dependent on input frequency.

18. Frequency Discrimination(Slope Detection) technique: H(f) Envelope Detector sc(t) sd(t) s(t) t t Sc(t) S(t) Sd(t) t

19. Problems:- 1>The detector also responds to spurious amplitude variation of the input FM. 2> The range of linear slope is quite small. |H(f)| f f0fc

20. Frequency Demodulation using Phase Locked Loop:- PLL is useful in FM demodulation in presence of large noise and low signal power. Thus it finds application in space vehicle to earth data links. Recently it is being used in Commercial FM receiver.

21. Phase Locked Loop:- A PLL is basically a negative feedback system. It consists of three major components: A multiplier A loop filter A voltage controlled oscillator(VCO) These are connected together in the form of a feedback loop. Loop Filter X FM wave s(t) e(t) v(t) r(t) VCO

22. Circuit for Direct FM generation:- FM OSCILLATOR Sound Wave L C Condenser Microphone

23. Varactor Diode Modulator:- -Vcc Cc em(t) FM L C Varactor Diode

24. Practical Reactance Modulator:- +Vcc RFC R1 RFC R1 Oscilator Reactance Modulator C FM output C1 R2 R RE CC RE CE C2 C CE R2 CB Modulating signal

25. FM Receiving System:- Frequency changer circuit

26. FM receiver circuit:- The application circuit to generate FM(88-108 MHz) with stereo headphone amplifier

27. The Stereo FM

28. What Stereo Means :-

29. How then comes the virtualization ??

31. We need :---- An input signal Two preemphasizers A DSB-SC modulator A frequency doubler A pilot signal A summer An FM modulator

34. Why do we need L + R & L – R?? Compatibility issue A mono phonic receiver will work with only the L+R component and there will no loss of AUDIO(so the signal will have the backward compatibility)

36. We need :---- An input signal (through a LIMITER DISCRIMINATOR) A Low Pass Filter(0-15 KHz) A Bandpass Filter(19 KHz) A Bandpass Filter( 23 – 53 KHz) A pilot signal A Frequency Doubler A Synchronous Detector Two Deephasizers

38. What is a Limiter discriminator ??

39. What is a preemphasizer ??

40. Preemphasizer refers to a system process designed to increase, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system.

43. A preemphasizer Network

44. What is a deemphasizer ??

45. Deemphasizer refers to a system process designed to decrease, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system.

48. A Deemphasizer Network

49. QUESTIONS ARE WELCOME