Presentation on theme: "Intelligent Islamic Electrical Engineers (IIEE)"— Presentation transcript:
1 Intelligent Islamic Electrical Engineers (IIEE) Communications LAB I Amplitude Modulation DSB-LC (Full AM) presentationUNDER SUBERVISION:Eng. Mohammed k. Abu FoulDesign by :Intelligent Islamic Electrical Engineers (IIEE)presentation by:Mahmood A. El-TatarIslame E. AshoorMohaned H. Eqdeeh
2 Signals in Communications Base bandBandpassAmplitudemodulationAnglePhase MOD.PMFrequency MOD.FMDSB-SC MOD.DSB+C MOD.SSB MOD.VSB MOD.
3 Analog Communication system Information sourceSignal modulatorPropagation channelSignal demodulatorInformation output
4 Amplitude Modulation: There are 4 main types of AM signals:Full Am – 2 sidebands and carrier.Double sideband suppressed carrier (DSB-SC).Single sideband AM (SSB).Vestigial sideband AM (VSB).
5 Amplitude Modulation DSB-LC (Full AM) Full AM is sometimes referred to as Double Side Band – Large Carrier (DSLC)clearly indicating its main feature as having a large amplitude carrier componentadded to the signal spectrum.Type of modulators :1-multiplier mod.2-nonlinear mod.3- switching mod.
8 Modulation index If we consider : We defined modulation index to be f(t)= Am cos(wm*t), c(t)= Ac cos(wc*t)Φ(t)= (Am+Ac) cos(wm*t) cos(wc*t)We defined modulation index to beM= Am/AcThus we have:Φ(t)= Ac(1+m cos(wm*t))* cos(wc*t)In order to detect the signal with no distortion we require m ≤1
9 Matlap code fc=20000; ts=1/(10*fc); t=[0:2000]*ts; fs=1/ts; m=.25; Ac=4;x = (cos(2*pi*2000*t)).^3figure(1)subplot(221)plot(t,x)title('plot of baseband signal x(t)')xlabel('time (t)')ylabel('x(t)')Xf=fftshift(fft(x))/length(t);deltax=fs/length(Xf);fx=-fs/2:deltax:fs/2-deltax;subplot(222)plot(fx,abs(Xf))title('the fourier transform of x(t)')xlabel('frequency (f)')ylabel('X(f)')y=(1+m*x)*Ac.*cos(2*pi*fc*t);subplot(223)plot(t,y)%%title('the modulated signal y(t)=(1+m*x)*Ac.*cos(2*pi*fc*t)')ylabel('y(t)')yf=fftshift(fft(y))/length(t);delta=fs/length(yf);f=-fs/2:delta:fs/2-delta;subplot(224)plot(f,abs(yf))ylabel('Y(f)')
10 Demodulation of Full AM (1) Coherent Demodulation:consists of multiplying received signal with a local carrier and filtering out unwantedcomponents centered around 2wc.
11 Filters Types Of Filters: We will use the Butterworth filter in our study .Types Of Filters:LPFBPFHPFBRF
12 HOW TO MAKE LPFTo get the Butterworth filter order and cutoff frequency we use this code :Wp=5000/fs;Ws=20000/fs;Rp=-1;Rs=-100;[N, Wn] = BUTTORD(Wp, Ws, Rp, Rs)[num,den]=butter(N,Wn)v=filter(num,den,w)Where:Wp :Passband corner frequency.Ws: Stopband corner frequency .Rp&Rs : ripple factor .N : Filter orderWn: cutoff frequencynum, den: filter transfer function
13 Matlap code w=y.*cos(2*pi*fc*t) figure(3) subplot(211) plot(t,w) title('plot of demodulated signal w(t) before LPF')xlabel('time (t)')ylabel('w(t)')wf=fftshift(fft(w));wf=wf/length(wf);delta=fs/length(wf);f=-fs/2:delta:fs/2-delta;subplot(212)plot(f,abs(wf))title('fourier transform of the demodulated signal W(f)')xlabel('frequency (f)')ylabel('W(f)')Wp=5000/fs;Ws=20000/fs;Rp=-1;Rs=-100;[N, Wn] = BUTTORD(Wp, Ws, Rp, Rs)[num,den]=butter(N,Wn)v=filter(num,den,w)figure(4)plot(t,v)title('the demodulated signal after LPF v(t)')ylabel('v(t)')Vf=fftshift(fft(v))/length(t);deltav=fs/length(Vf);fv=-fs/2:deltav:fs/2-deltav;plot(fv,abs(Vf))title('the fourier transform of v(t)')ylabel('V(f)')
14 (2) Envelope DetectorThe output of the detector follows the envelope of the modulated signal.On positive half-cycle of RF input signalΦ(t), the diode is forward biased and thecapacitor C charges up rapidly to the peakvalue of RF input signalWhen RF input falls below the outputvoltage then the diode becomes reversebiasedand the capacitor C dischargesthrough the load resistor RL
15 1/fc << RC<< 1/B RC effectiveChoice of R and C:1/fc << RC<< 1/BWhere B is the highest frequency in f(t) (original signal)Where fc is the carrier frequency
16 Matlap code R=3.2e3; C=01e-6; RC=R*C; Vout(1)=y(1); for i=2:length(y); if y(i)>Vout(i-1)Vout(i)=y(i);elseVout(i)=Vout(i-1)*exp(ts/RC);endfigure(3)plot(t,Vout,t,y)xlabel('time (t)')ylabel('v(t)')
18 conclusionClearly, main advantage of Full AM modulation is very simple and cost effective demodulation of the signal at the receiving end.But AM is as wasteful of spectrum as DSB-SC and requires a large carrier amplitude which in turns require more overall power to be transmitted.(Transmission of carrier is a waste of power since it does not carry information except its phase and frequency).
19 GUI TOOLThis tool is used to give a simple understanding of this experiment and generally of the amplitude modulation.You can use itENJOY
20 Intelligent Islamic Electrical Engineers IIEESoon … in Al-Aqsa