How to make bandpass filter?

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Andrew 2012-11-28

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Dear community, I have got a signal with a noise. Frequency of this noise is 50 kHz. How can I cut it off? What is the easiest way to make bandpass filter? Thanks in advise.

Andrew

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Answer 1

Wayne King 2012-11-28

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编辑：Wayne King 2012-11-28

在 MATLAB Online 中打开

OK, then you can do two filters. A highpass filter and a notch filter (I'll assume you have fdesign.notch)

    d = fdesign.highpass('Fst,Fp,Ast,Ap',2500,3000,60,0.5,5e6);
    Hd1 = design(d,'butter');
    d2 = fdesign.notch('N,F0,Q',10,5e4,35,5e6);
    Hd2 = design(d2);
    Hd = cascade(Hd1,Hd2);

Now you can use Hd to filter data.

out = filter(Hd,input);

You can view the filter with

fvtool(Hd,'Fs',5e6)

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Andrew 2012-11-28

Thank you very much!

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Answer 2

Wayne King 2012-11-28

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You have to know your sampling frequency, but you can you use fdesign.bandpass

Also when you specify the frequency of the noise as 50 kHz, are you saying that the "noise" is sinusoidal, only occurring at 50 kHz? If so, then a notch filter would be appropriate. If you have the DSP System Toolbox see fdesign.notch.

If you describe your the frequency band of interest (what you want to keep) and the sampling frequency, we can help you better. For example, it may be that a lowpass filter would be appropriate.

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Andrew 2012-11-28

编辑：Andrew 2012-11-28

I have a wanted signal with noise. The sampling rate is 5 MHz. The frequencies of this noise are 1-3 kHz and 50 kHz. So I want to cut off this frequencies and keep all other.

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Answer 3

Wayne King 2012-11-28

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With a 5 MHz sampling rate and what you want, it's going to be a very expensive filter, do you really need to keep frequencies below 1 kHz at that sampling rate? Or can you just get rid of everything below 3 kHz?

Or do you really need to have the data sampled at 5 MHz? Can you downsample to a lower sampling rate?

Also, you did not answer the question about the noise at 50 kHz. Is it sinusoidal?

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Andrew 2012-11-28

Yes, the noise at 50 kHz is sinusoidal. I don't want to downsample, because the wanted is signal is fluctuation, so I need to keep sampling frequency. Sorry, I have made a mistake, I can get rid of everything bellow 3kHz.

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