This presentation includes concepts of FM, generation of FM, transmission, reception, with the concepts of stereo FM and some basic circuitry of receiver and transmitter system.

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

5. 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. em (t) _ NBFM
Integrator Product ∑
Modulator
+
Accos(2Πfct)
Phase Shifter
Narrow – Band Phase Modulator

8. 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. 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.
The bandwidth of FM wave is much larger than AM wave.

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

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

14. Direct Method of FM generation:----
Base band VCO Frequency Frequency Bandpass WBFM
Mixer
Signal Multiplier Multiplier Filter
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:-
Base Band Frequency stabilized
VCO
Signal FM wave
LPF & Frequency Crystal
Mixer
Amplifier Discriminator 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:
1. Based on Frequency Discrimination
2. 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)
sc(t) Envelope sd(t)
s(t) Detector
t t
S(t) Sc(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)|
f0 fc f

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:
1. A multiplier
2. A loop filter
3. A voltage controlled oscillator(VCO)
These are connected together in the form of a feedback loop.
FM wave e(t)
s(t) X Loop Filter v(t)
r(t)
VCO

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

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

24. Practical Reactance Modulator:-
+Vcc
RFC R1 RFC
R1
Reactance Oscilator
C
Modulator
C1 FM
output
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

28. What Stereo Means :-

29. How then comes the
virtualization ??

30. What do we need for the
transmission?
• We need two different signals L(left) &
R(right) to be modulated, transmitted, received
and demodulated duly without getting distorted

32. We need :----
a.An input signal
b.Two preemphasizers
c.A DSB-SC modulator
d.A frequency doubler
e.A pilot signal
f. A summer
g.An FM modulator

35. Why do we need L + R & L – R??
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)

37. We need :----
a. An input signal (through a
LIMITER DISCRIMINATOR)
b. A Low Pass Filter(0-15 KHz)
c. A Bandpass Filter(19 KHz)
d. A Bandpass Filter( 23 – 53 KHz)
e. A pilot signal
f. A Frequency Doubler
g. A Synchronous Detector
h. Two Deephasizers

41. 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.

46. 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.

50. QUESTIONS ARE WELCOME