how can i apply lowpass filter to this code

% generate a waveform

f0 =100;

fs=1000;

pw = 0.1;

pri = 1;

npulses = 100;

s = cos(2*pi*f0*(0:1/fs:pw)); % it can be any other waveform of your choice

s(round(fs*pri)) = 0; % PRI

s = repmat(s, npulses, 1); % npulses

% echo: delayed signal

tau = 0.3;

ntau = round(fs*tau);

amp = 0.5;

e = amp* circshift(s, ntau);

% add noise

sigma = 0.1;

r = s + e + sigma*randn(size(s));

y = pulsint(r);

plot((0:length(s)-1)/fs, r)

Answer 1

[Star Strider]

There are several approaches. This one uses the lowpass function —

% generate a waveform 
f0 =100;  
fs=1000;  
pw = 0.1; 
pri = 1; 
npulses = 100;
s = cos(2*pi*f0*(0:1/fs:pw));      % it can be any other waveform of your choice
s(round(fs*pri)) = 0;               % PRI
s = repmat(s, npulses, 1); % npulses
% echo: delayed signal
tau = 0.3;  
ntau = round(fs*tau); 
amp = 0.5;
e = amp* circshift(s, ntau);
% add noise
sigma = 0.1;
r = s + e + sigma*randn(size(s));
y = pulsint(r);

Fn = fs/2

Fn = 500

Fco = 125;                                                      % Choose A Frequency > 0 & < fs/2
r_filt = lowpass(r, Fco, fs, 'ImpulseResponse','iir');          % Design An Elliptic Filter & Filter 'r'

figure
plot((0:length(s)-1)/fs, r)
title('Original')

figure
plot((0:length(s)-1)/fs, r_filt)
title('Filtered')

Thje amplitude is less in the filtered signal because signal energy has been removed. Use the fft or pspectrum function on both signals to see the effect of filtering.

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