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Communication 1 (lab)

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.

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Communication 1 (lab)

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  1. Communication 1 (lab) Frequency modulation (FM) Morad El-masryAhmad Farwana Mohammad sabbah Eng. Mohammad K. AbuFoul 2010

  2. Contents • Introduction ( P1-P4). • Frequency modulation .(P5-P7) • Frequency demodulation (P8-P14) • FM using simulink implementation (P15 – P 17)

  3. Introduction 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 .

  4. The Baseband signal This is how the FM and the AM carriers carry the information . AM carrier FM carrier

  5. 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 signal The baseband frequency is 1 Hz

  6. The wave form and the magnitude spectrum The baseband signal is tow pulses at 1 and -1 Hz

  7. Modulation : To modulate a NBFM signal we first Integrate the baseband signal then we modulate it using DSB-sc

  8. Matlab work : 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

  9. 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

  10. Demodulation : There are tow methods to demodulate the signal - The first method is the direct differentiation method : (using the op-amp as differentiator )

  11. The second method is the slope detection method (vco) : ( tank circuit and envelop detector -Voltage-controlled oscillator )

  12. 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

  13. The wave form and the magnitude spectrum of the demodulated signal Now its obvious that the envelop is shown we can use envelop detector

  14. 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

  15. The demodulated signal and the envelop of the baseband signal

  16. The envelop ( baseband signal ) = sin (2*pi*t)

  17. Simulink implementation : First we draw the circuit as shown in the figure

  18. The baseband signal The output of the VCO

  19. The FM signal The demodulated signal ( ready for envelop detection )

  20. With our best wishes

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