I have a data set which includes 2 columns: one is time (in month) and one is values that need analysics. I need to used bandpass filer to filter signal and obtain quasi-beninial oscillation (QBO) as figure 6(in attach). The period of this QBO is from 22 to 34 months, centered at 28 months. I try wirte a code but I don't belive on it. I would like everyone to check help me. My data, code, figure in attach. I hope everyone can help me.