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);