n=4;
rect=Piecewise1,0<=x≤
1
n

1
0≤x≤
1
4
0
True
Plot[rect,{x,-1,1}]
-1.0
-0.5
0.5
1.0
0.2
0.4
0.6
0.8
1.0
conv=Convolve[rect,Sin[x]*DiracComb[x*n],x,y]
Convolve
1
0≤x≤
1
4
0
True
,DiracComb[4x]Sin[x],x,y
Plot[conv,{y,0,2*Pi},PlotRangeAll]
1
2
3
4
5
6
-0.2
-0.1
0.1
0.2
(*list=TableNconv
1
100
*i,{i,100}*)
N[conv[1]]
Convolve

1.
0.≤x≤0.25
0.
True
,DiracComb[4.x]Sin[x],x,y[1.]