design filter , Hello everyone, I'm trying to run a script I've written that deals with signal modulation and frequency filtering. unfortunately, the software is crashing at runtime while its deal with the "bode", what can i do?

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Guni Basilian 2019-11-18

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评论： Star Strider 2019-11-18

Hello everyone, I'm trying to run a script I've written that deals with signal modulation and frequency filtering. unfortunately, the software is crashing at runtime while its deal with the "bode", what can i do?

clc

close all

clear all

m=1;

am=1.8;

fa=20; %400Hz

ta=1/fa;

t=0:ta/999:6*ta;

ym=am*sin(2*pi*fa*t);

figure(1)

subplot(3,1,1);

plot(t,ym)

title('Modulating signal')

ac=am/m;

fc=400000; %400KHz

% tc=1/fc;

% yc=ac*sin(2*pi*fc*t);

yc= am+ac*square(2*pi*fc*t);

subplot(3,1,2);

plot(t,yc);

grid on;

title('Carrier signal')

y=ac+(1+m*sin(2*pi*fa*t)).*square(2*pi*fc*t);

subplot(3,1,3);

plot(t,y);

title('am signal');

grid on

nfft=length(y);

nfft2=2^nextpow2(nfft);

ff=fft(y,nfft2);

figure(2)

plot(abs(ff))

Fs = length(nfft2);

xdft = fftshift(fft(y));

df = Fs/length(y);

freq = -Fs/2:df:Fs/2-df;

plot(freq,abs(xdft))

Fstop = 350;

Fpass = 400;

Astop = 65;

Apass = 0.5;

Fs = 1e3;

d = designfilt('highpassiir','StopbandFrequency',Fstop ,...

'PassbandFrequency',Fpass,'StopbandAttenuation',Astop, ...

'PassbandRipple',Apass,'SampleRate',Fs,'DesignMethod','butter');

figure(3)

fvtool(d);

[a,b]=tf(d);

filter=tf(a,b);

yfilter=y*filter;

figure(4)

bode(y);

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Answer 1

Star Strider 2019-11-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/491664-design-filter-hello-everyone-i-m-trying-to-run-a-script-i-ve-written-that-deals-with-signal-modul#answer_402042

The bode function is part of the Control System Toolbox (and friends). It takes a system object as an argument. Also, multiplying system objects is the same as connecting them in series, so ‘yfilter’ will not do what you want. If you want the Bode plot of a filter, use the freqz (or freqs) functions, instead. If you want to filter a signal with a Signal Processing Toolbox filter, use the filtfilt function to do the actual filtering.

Please do not name your variables filter or anything else that could overshadow a MATLAB function name.

Your code otherwise appears to be good, and produces a double-sideband-transmitted-carrier AM signal.

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Guni Basilian 2019-11-18

thanks a lot! this is vwry helpfull. how can i menege to compain this freqz func in my function? do i need to multiply it like transfer function?

Star Strider 2019-11-18

As always, my pleasure!

The freqz funciton will plot the Bode plot of your filter. Please do not multiply it by anything. If you want to use your filter to filter your signal, use the filtfilt function with it.

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