By harnessing the heterogeneous combination of waveplates, we demonstrated a wavelength-tunable passband-squeezed polarization-diversified fiber loop (PDFL) comb filter. The PDFL comb filter is composed of a polarization beam splitter (PBS), two polarization-maintaining fiber (PMF) segments of the same length, one waveplate combination (WC) of dual quarter-wave plates (QWPs), and another WC of a QWP and a half-wave plate. The former and latter WCs are located before the first and second PMF segments, respectively, and the second PMF is butt-coupled to the PBS so that its slow-axis orientation angle (OA) should be 22.5 deg for the horizontal axis of the PBS. This is the first report on the implementation of the wavelength tunability in the passband-squeezed PDFL comb filter using this heterogeneous WC. Through the Jones calculus, we derived the sinusoidal passband-squeezed transmittance function of the filter. From the derived transmittance, we found the slow-axis OA sets of the four waveplates where the extra phase ϕ of the transmittance function could be continuously changed from 0 deg to 360 deg and graphically represented these OA sets as functions of ϕ along with the relationship between the OA sets. For eight OA sets selected from these OA sets, allowing ϕ to regularly increase from 0 deg to 315 deg by 45 deg, we calculated the passband-squeezed transmission spectra of the filter and confirmed a redshift of the passband-squeezed spectrum by 0.1 nm per set. Then, this theoretical prediction was validated by experimental verification, which corroborates that our filter can offer the wavelength tunability of the passband-squeezed comb spectrum.