This paper deals with the theory in which the K-L transform suppresses the noise. Through research and analysis

of the theoretical model, the authors have reached the following conclusion: although the K-L transform filtering can

suppress the inclined coherent signal, it can also blur the fault signal if the characteristic value chosen is not

suitable. It is thus held that, as the noise-suppressing technology can destroy the effective signal, one must be careful

in using it or even should avoid using it in the work.