Examples of the absolute value of the normalized Faraday Dispersion Function (FDF), obtained from two LOFAR observations. The peaks at zero Faraday depth, F(φ ≈ 0), indicate the instrumental response. Left: FDF obtained from a single 3-min HBA observation (119–125 MHz) of PSR B2217+47. The peak at F(φ = −34.08  rad  m^-2) is the response due to the polarized flux of the pulsar. The FWHM of the RMSF is 6.6 rad m^-2. Right: FDF obtained from a single 3-min LBA observation (58–64 MHz) of PSR B1919+21. The polarized flux of the pulsar is responsible for the peak at F(φ = −15.94  rad  m^-2). The FWHM of the RMSF is 0.84 rad m^-2.