  The design and performance of a sensitive and reliable cross-correlation
spectrum analyzer for studying low frequency transport noise is described in
detail. The design makes use of common PC-based data acquisition hardware and
preamplifiers to acquire time-based data, along with software we have developed
to compute the cross-correlation and noise spectral density. The impedance of
device under test may cover four decades from ${100\,{\Omega}}$ to
${1\,{\mathrm{M}\Omega}}$. By utilizing a custom developed signal processing
program, this system is tested to be accurate and efficient for measuring
voltage noise as low as $\sim\!10^{-19}\,\mathrm{V}^2/\mathrm{Hz}$ from
${0.001\,}$Hz to ${100\,}$kHz within one day's averaging time, comparable with
more expensive hardware solutions (bandwidth in real measurements may be
limited by the sample impedance and stray capacitance). The time dependence of
measurement sensitivity is discussed theoretically and characterized
experimentally to optimize between measuring time and accuracy. A routine for
noise component analysis is introduced, and is applied for characterizing the
noise spectra of metal and carbon film resistors, revealing an almost strict
$1/$frequency dependence that may reflect an ensemble of random resistivity
fluctuation processes with uniformly distributed activation energies. These
results verify the general applicability of this analyzer for low level noise
researches.
