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function xl=loweq(x,ts,f0) 
%       xl=loweq(x,ts,f0) 
%LOWEQ      returns the lowpass equivalent of the signal x 
%       f0 is the center frequency.  
%       ts is the sampling interval. 
%    
t=[0:ts:ts*(length(x)-1)];   
z=hilbert(x); 
xl=z.*exp(-j*2*pi*f0*t);