How can I do/implement Low pass filter function in matlab?

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Mohamed Jamall 2020-6-22

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评论： Satyam 2023-11-2

Hi !

how can I use/do LOW PASS FILTER in matlab? I want to determine as inputs the cut off frequency .. and I want also as second input to enter to LOW PASS FILTER the signal (it's a vector) , so Im trying to do LOW PASS FILTER function called function Low_Pass_Filter(first input the cutoff frequency that I want to input it to my LOW PASS FILTER, Second input is the signal which it's a vector 1X10k size) .. any help please how can I do that in matlab?

thanks alot!

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Satyam 2023-11-2

type fdatool in matlab command prompt and there you will get all options for realizing a filter

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Answer 1

Star Strider 2020-6-22

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This is already available in the lowpass function (introduced in R2018a).

Otherwise, it is straightforward to define filters with the Signal Processing Toolbox functions. Note that you need to define the sampling freuqency of the signal in order to define the cutoff frequency correctly.

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Star Strider 2020-6-22

在 MATLAB Online 中打开

You are welcome to explore the lowpass code on your own at your leisure.

Here is some archive example code, with the time vector ‘t’ and ‘signal’ the vector to be filtered:

Fs = 1/mean(diff(t));                                               % Sampling Frequency
L = numel(t);                                                       % Signal Length
Fn = Fs/2;                                                          % Nyquist Frequency
Wp = 0.05/Fn;                                                       % Passband Frequency (Normalised)
Ws = 0.06/Fn;                                                       % Stopband Frequency (Normalised)
Rp =  1;                                                            % Passband Ripple
Rs = 60;                                                            % Passband Ripple (Attenuation)
[n,Wp] = ellipord(Wp,Ws,Rp,Rs);                                     % Elliptic Order Calculation
[z,p,k] = ellip(n,Rp,Rs,Wp,'low');                                  % Elliptic Filter Design: Zero-Pole-Gain 
[sos,g] = zp2sos(z,p,k);                                            % Second-Order Section For Stability
figure
freqz(sos, 2^16, Fs)                                                % Filter Bode Plot
signal_filt = filtfilt(sos, g, signal);                             % Filter Signal

Note that this code has a passband frequency of 0.05 Hz and a stopband frequency of 0.06 Hz. Use values that make sense in your application.

See the documentation for the various functions to understand how they work, and the reason I use them.

This is one of many examples of filter design I have posted over the years. For more of them, search Answers.

.

Mohamed Jamall 2020-6-22

编辑：Mohamed Jamall 2020-6-22

THANKS ALOT!

I understand the code, but there's something that Im missing, lets assume my frequency of transmitted data(I transmit RF PACKETS) is 868MHZ, symbol rate (bit rate) is 50Kbouad , sampling frequency is 2048K .

so if I want to do my Low Pass filter that the cut off of my LPF will be 50KBOAUD , what should I do? here's my problem. I want that my cutoff frequency of my LPF to be my symbol rate ..

thanks in advance for any assistance! appreciate!!!!

Star Strider 2020-6-22

My code is intended for signal processing, not communications. I have essentially no experience with digital communications protocols. You will need to experiment to be certain my code does what you want in your application.

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How can I do/implement Low pass filter function in matlab?

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