i=10;
Wn1 = [(700-i)*2/fs,(700+i)*2/fs];
[b2,a2] = butter(1,Wn1,'stop');
n = 1400;
while n < fs/2
	Wn1 = [(n-i)*2/fs,(n+i)*2/fs];
	[bt,at] = butter(1,Wn1,'stop');
	b2=conv(b2,bt);
	a2=conv(a2,at);
    n = n + 700;
end
fvtool(b2,a2);