Frequency Modulation & Demodulation of a signal

To perform Frequency Modulation & Demodulation of a signal

 

Program:

 

%% Matlab code for FM encoder decoder

Fs = 8000; % Sampling rate of signal

Fc = 3000; % Carrier frequency

t = [0:Fs]/Fs; % Sampling times

s1 = sin(2*pi*10*t); % Channel 1

%s2 = sin(2*pi*150*t)+2*sin(2*pi*900*t); % Channel 2

%x = [s1]; % Two-channel signal

dev = 50; % Frequency deviation in modulated signal

y = fmmod(s1,Fc,Fs,dev); % Modulate both channels.

z = fmdemod(y,Fc,Fs,dev); % Demodulate both channels.

subplot(2,1,1); plot(t,y); title('frequency modulated image');% Plot x on top.

subplot(2,1,2); plot(t,z);title('demodulated image');% Plot y below.

FIR filter matlab code

Matlab code for Finite impulse response (FIR) filters.

EQUIPMENTS:

Operating System         – Windows XP

Constructor                  - Simulator

Software                      - CCStudio 3 & MATLAB 7.5

THEORY:

A Finite Impulse Response (FIR) filter is a discrete linear time-invariant system whose output is based on the weighted summation of a finite number of past inputs. An FIR transversal filter structure can be obtained directly from the equation for discrete-time convolution.

                                           

In this equation, x(k) and y(n) represent the input to and output from the filter at time n.  h(n-k) is the transversal filter coefficients at time n. These coefficients are generated by using FDS (Filter Design Software or Digital filter design package).

FIR – filter is a finite impulse response filter. Order of the filter  should be specified. Infinite response is truncated to get finite impulse response. placing  a window of finite length does this. Types of windows available are Rectangular, Barlett, Hamming, Hanning, Blackmann window etc. This FIR filter is an all zero filter.

PROGRAM:

%fir filt design  window techniques

clc;

clear all;

close all;

rp=input('enter passband ripple');

rs=input('enter the stopband ripple');

fp=input('enter passband freq');

fs=input('enter stopband freq');

f=input('enter sampling freq ');

wp=2*fp/f;

ws=2*fs/f;

num=-20*log10(sqrt(rp*rs))-13;

dem=14.6*(fs-fp)/f;

n=ceil(num/dem);

n1=n+1;

if(rem(n,2)~=0)

    n1=n;

    n=n-1;

end

c=input('enter your choice of window function 1. rectangular 2. triangular 3.kaiser: \n ');

if(c==1)

    y=rectwin(n1);

    disp('Rectangular window filter response');

end

if (c==2)

    y=triang(n1);

   disp('Triangular window filter response');

end

 if(c==3)

     y=kaiser(n1);

   disp('kaiser window filter response');

 end

%LPF

b=fir1(n,wp,y);

[h,o]=freqz(b,1,256);

m=20*log10(abs(h));

subplot(2,2,1);plot(o/pi,m);

title('LPF');

ylabel('Gain in dB-->');

xlabel('(a)         Normalized frequency-->');

%HPF

b=fir1(n,wp,'high',y);

[h,o]=freqz(b,1,256);

m=20*log10(abs(h));

subplot(2,2,2);plot(o/pi,m);

title('HPF');

ylabel('Gain in dB-->');

xlabel('(b)         Normalized frequency-->');

%BPF

wn=[wp ws];

b=fir1(n,wn,y);

[h,o]=freqz(b,1,256);

m=20*log10(abs(h));

subplot(2,2,3);plot(o/pi,m);

title('BPF');

ylabel('Gain in dB-->');

xlabel('(c)         Normalized frequency-->');

%BSF

b=fir1(n,wn,'stop',y);

[h,o]=freqz(b,1,256);

m=20*log10(abs(h));

subplot(2,2,4);plot(o/pi,m);

title('BSF');

ylabel('Gain in dB-->');

xlabel('(d)         Normalized frequency-->');

 

 

 

Matlab filters

AIM:

To verify response of analog Low pass filter (LPF) & High pass filter(HPF) using MATLAB

 

EQUIPMENTS:

Operating System         – Windows XP

Constructor                  - Simulator

Software                      - CCStudio 3 & MATLAB 7.5

THEORY:

Analog Low pass filter & High pass filter are obtained by using butterworth or chebyshev filter with coefficients are given. The frequency – magnitude plot gives the frequency response of the filter.

PROGRAM:

 

Matlab code for filters

%  IIR filters LPF & HPF

clc;

clear all;

close all;

warning off;

disp('enter the IIR filter design specifications');

rp=input('enter the passband ripple');

rs=input('enter the stopband ripple');

wp=input('enter the passband freq');

ws=input('enter the stopband freq');

fs=input('enter the sampling freq');

w1=2*wp/fs;w2=2*ws/fs;

[n,wn]=buttord(w1,w2,rp,rs,'s');

c=input('enter choice of filter 1. LPF 2. HPF \n ');

if(c==1)

    disp('Frequency response of  IIR LPF is:');

[b,a]=butter(n,wn,'low','s');

end

if(c==2)

    disp('Frequency response of  IIR HPF is:');

[b,a]=butter(n,wn,'high','s');

end

w=0:.01:pi;

[h,om]=freqs(b,a,w);

m=20*log10(abs(h));

an=angle(h);

figure,subplot(2,1,1);plot(om/pi,m);

title('magnitude response of  IIR filter is:');

xlabel('(a) Normalized freq. -->');

ylabel('Gain in dB-->');

subplot(2,1,2);plot(om/pi,an);

title('phase response of  IIR filter is:');

xlabel('(b) Normalized freq. -->');

ylabel('Phase in radians-->');