  Universal conductance fluctuations are usually observed in the form of
aperiodic oscillations in the magnetoresistance of thin wires as a function of
the magnetic field B. If such oscillations are completely random at scales
exceeding \xi_B, their Fourier analysis should reveal a white noise spectrum at
frequencies below \xi_B^{-1}. Comparison with the results for 1D systems
suggests another scenario: according to it, such oscillations are due to the
superposition of incommensurate harmonics and their spectrum should contain
discrete frequencies. An accurate Fourier analysis of the classical experiment
by Washburn and Webb reveals a practically discrete spectrum in agreement with
the latter scenario. However, this spectrum is close in shape to the discrete
white noise spectrum whose properties are similar to a continuous one. More
detailed analysis reveals the existence of the continuous component, whose
smallness is explained theoretically. A lot of qualitative results are
obtained, which confirm the presented picture. The distribution of phases,
frequency differences and the growth exponents agree with theoretical
predictions. Discrete frequencies depends weakly on the treatment procedure.
The discovered shift oscillations confirm the analogy with 1D systems.
Microscopical estimates show agreement of the obtained results with geometrical
dimensions of the sample.
