Examples of three spectral break sources of our samples. Top row: spectral fit of SPECFIND V3.0. Bottom row: spectral fit of the spectral break with vertical dashed line at the selection frequency, where the subsamples were divided. Left: MPS source candidate NVSS J123048+485758. In SPECFIND V3.0 the left part of the spectrum was ignored for most of the spectral fits. Middle: concave source candidate NVSS J080637+774606. The peak frequency point at 1.4 GHz was not included in SPECFIND V3.0. Right: GPS source candidate NVSS J120215+720024. The low-frequency part of the spectrum was not included in SPECFIND V3.0.