def get_kx(N,dx):
    """
    GET_KX
    :summary: Returns the frequencies to be used with FFT analysis
    
    :parameter N: number of samples in data
    :parameter dx: sampling step
    
    :return: Returns
      * k: frequency
      * L: length
      * imx: index of maximum frequency (for separating positive and negative frequencies)
    
    :author: Renaud DUSSURGET (RD) - LER/PAC, Ifremer
    :change: Created by RD, July 2012
    """
    
    # to work with dimensional axes
    L = N*dx
    
    #Odd or even
    odd = N&1 and True or False
    
    #Get frequency & wavenumber
    k=ft.fftfreq(N,d=dx)
#    k=f*N
    
    imx = (N-1)/2 if odd else N/2 #Maximum frequency
    
    #Convert into frequencies
#    k/=L
    
    return k, L, imx