B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

242 ANGLE MODULATION AND DEMODULATION
Figure 5.18
(a) FM stereo
transmitter. (b)
Spectrum of a
baseband stereo
signal. (c} FM
stereo receiver.
L
r------. (L + R)'
Preemphasizert------------
Frequency
doubler
R
L-R
Preemphasizer
DSB-SC
modulator
(a)
Composite
baseband
(b)
53 -
f, kHz
(L + R)
.-------.
LPF
1---------1 Deemphasizer
0-15 kHz
Limiterdiscriminator
NBF
19 kHz
Frequency
doubler
5.8 MATLAB EXERCISES
BPF Synchronous
t Deemphasizer
23-53 kHz demodulator
(L - R)' cos w e t (L - R)' (L - R )
( c)
In this section, we use MATLAB to build an FM modulation and demodulation example. The
MATLAB program is given by ExampleFM . m. Once again use apply the same message
signal m2 (t). The FM coefficient is kJ = 80 and the PM coefficient is k p
= n. The carrier
frequency remains 300 Hz. The resulting FM and PM signals in the time domain are shown in
Fig. 5.19. The corresponding frequency responses are also shown in Fig. 5.19. The frequency
domain responses clearly show the much higher bandwidths of the FM and PM signals when
compared with amplitude modulations.
% (ExampleFM.m)
% This program uses triangl .m to illustrate frequency modulation
% and demodulation