I am in Chapter 5 of "Understanding Digital signal processing" 3rd edition by Richard G. Lyons. I am stuck with Section 5.4.
In order to get the bandpass filter centred at $F_s/4 \mathrm{Hz}$, I need to multiply the low pass filter coefficients by a sinusoid of $F_s/4 \mathrm{Hz}$ samples at 4 samples per cycle. I have tried to do this in MATLAB but cannot figure out how to sample at four samples per cycle. Since samplerate was not given, I created a sinusoid: $$ n=0:30;\\ x=\sin(n\pi/2)% $$ Is this correct for $F_s/4$ signal?
How do I sample it at four samples per cycle in MATLAB?
I feel like I missing something very fundamental.