In[]:=
cy=Array[Cos[30*2.Pi((#-1.0)/150)]&,150];Periodogram[cy,GridLines->Automatic,GridLinesStyle->Thickness[Medium],AspectRatio->1/5,ImageSize->Full]
Out[]=
In[]:=
ListLinePlot[20Log[10,Abs[Fourier[cy]]][[1;;76]],GridLines->Automatic,GridLinesStyle->Thickness[Medium],DataRange->{0,75/150},PlotRange->All,AspectRatio->1/5,ImageSize->Full]
Out[]=
In[]:=
20Log[10,Abs[Fourier[cy]]][[31]]
Out[]=
15.7403
In[]:=
Periodogram[cy][[1,2,1,1,3,1,3,1,31]]
Out[]=
{0.202703,15.7403}
In[]:=
Periodogram[cy][[1,2,1,1,3,1,3,1,31,1]]74/75
Out[]=
0.2
In[]:=
Length[Periodogram[cy][[1,2,1,1,3,1,3,1]]]
Out[]=
75
In[]:=
Periodogram[cy,DataRange->{0,74/150},GridLines->Automatic,GridLinesStyle->Thickness[Medium],AspectRatio->1/5,ImageSize->Full]
Out[]=
