down convert a signal in matlab

To down convert a signal in Matlab, you can use the following steps:

1. Load the signal you want to down convert into Matlab.

   main.m
   signal = load('signal.mat');
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2. Choose a down conversion factor. This factor should be less than 1 if you want to decrease the frequency of the signal.

   main.m
   downFactor = 0.5;
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3. Determine the new sampling frequency that you want to use. This can be calculated as the original sampling frequency divided by the down conversion factor.

   main.m
   Fs_new = Fs * downFactor;
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4. Create a low-pass filter to remove frequencies above the new Nyquist frequency.

   main.m
   lpFilter = designfilt('lowpassfir', 'PassbandFrequency', Fs_new/2, 'StopbandFrequency', Fs_new/2*1.1, ...
                          'PassbandRipple', 0.5, 'StopbandAttenuation', 60, 'DesignMethod', 'kaiserwin');
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5. Apply the low-pass filter to the original signal using the Matlab function resample.

   main.m
   signal_downconverted = resample(signal, downFactor, 1, 'low');
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After these steps, the signal_downconverted will be the down converted version of the original signal.