communication 1 (lab)
DESCRIPTION
Communication 1 (lab). Frequency modulation (FM). Morad El- masry Ahmad Farwana Mohammad sabbah Eng. Mohammad K. AbuFoul 2010. Contents. Introduction ( P1-P4). Frequency modulation .(P5-P7) Frequency demodulation (P8-P14) FM using simulink implementation (P15 – P 17). Introduction. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/1.jpg)
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Contents
Introduction ( P1-P4).
Frequency modulation .(P5-P7)
Frequency demodulation (P8-P14)
FM using simulink implementation (P15 – P 17)
![Page 3: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/3.jpg)
To transmit or to receive a signal , you cant do that with the signal itself , too many signals will overlap each other. So that we need a carrier to do the mission, too many kinds of carriers can be used . AM, FM, PM …
The frequency modulation (FM) is a technique that conveys information over a carrier wave by varying its instantaneous frequency . Compared with the Amplitude modulation (AM) in which the amplitude of the carrier varied according to the information while the frequency keeps constant .
Introduction
![Page 4: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/4.jpg)
This is how the FM and the AM carriers carry the information .
The Baseband signal
AM carrier
FM carrier
![Page 5: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/5.jpg)
Matlab work:
First we put the carrier frequency at 100 Hz and the period as shown in the figure
Then we plot the time domain and the frequency domain figures of the baseband signalThe baseband frequency is 1 Hz
![Page 6: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/6.jpg)
The wave form and the magnitude spectrum
The baseband signal is tow pulses at 1 and -1 Hz
![Page 7: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/7.jpg)
To modulate a NBFM signal we first Integrate the baseband signal then we modulate it using DSB-sc
Modulation:
![Page 8: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/8.jpg)
Now to modulate the signal we have to integrate the baseband signal using (cumsum) order in matlab
Then we plot wave form and the magnitude spectrum of the modulated signal
Matlab work:
![Page 9: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/9.jpg)
The wave form and the magnitude spectrum of the modulated signal
Here we can see how is the frequency change according to the baseband signal
![Page 10: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/10.jpg)
There are tow methods to demodulate the signal -
The first method is the direct differentiation method :
(using the op-amp as differentiator )
Demodulation:
![Page 11: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/11.jpg)
The second method is the slope detection method (vco) :
( tank circuit and envelop detector -Voltage-controlled
oscillator )
![Page 12: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/12.jpg)
Matlab work:
The demodulated signal is the differentiation of the modulated signal
Then we plot wave form and the magnitude spectrum of the demodulated signal
![Page 13: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/13.jpg)
The wave form and the magnitude spectrum of the demodulated signal
Now its obvious that the envelop is shown we can use envelop detector
![Page 14: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/14.jpg)
Envelop detector:
To detect the baseband signal we use an envelop detector as shown
RC should be in the range :
1/Fc < RC < 1/B
![Page 15: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/15.jpg)
The demodulated signal and the envelop of the baseband signal
![Page 16: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/16.jpg)
The envelop ( baseband signal ) = sin (2*pi*t)
![Page 17: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/17.jpg)
Simulink implementation:
First we draw the circuit as shown in the figure
![Page 18: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/18.jpg)
The baseband signal
The output of the VCO
![Page 19: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/19.jpg)
The FM signal
The demodulated signal ( ready for envelop detection )
![Page 20: Communication 1 (lab)](https://reader035.vdocument.in/reader035/viewer/2022081501/56814248550346895dae71c8/html5/thumbnails/20.jpg)