def rn(x, af, rate):
    """ R(n) ratio for noise identification
    
        ration of MVAR to AVAR
    """
    (taus,devs,errs,ns) = at.adev(x,taus=[af*rate], data_type='phase', rate=rate) 
    oadev_x = devs[0]
    (mtaus,mdevs,errs,ns) = at.mdev(x,taus=[af*rate], data_type='phase', rate=rate)
    mdev_x = mdevs[0]
    rn = pow(mdev_x/oadev_x,2)
    return rn