  Faraday tomography is a powerful method to diagnose polarizations and Faraday
rotations along the line of sight. The quality of Faraday tomography is,
however, limited by several conditions. Recently, it is reported that Faraday
tomography indicates false signals in some specific situations. In this paper,
we systematically investigate the condition of the appearance of false signals
in Faraday tomography. We study this by pseudo-observing two sources within a
beam, and change in the intrinsic polarization angles, rotation measures,
intensities, and frequency coverage. We find that false signals arise when
rotation measure between the sources is less than 1.5 times the full width at
half maximum of the rotation measure spread function. False signals also depend
on the intensity ratio between the sources and are reduced for large ratio. On
the other hand, the appearance of false signals does not depend on frequency
coverage, meaning that the uncertainty should be correctly understood and taken
into consideration even with future wide-band observations such as Square
Kilometer Array (SKA).
