Aims. With the recent preliminary release of the LOFAR LBA Sky Survey
(LoLSS), the first wide-area, ultra-low frequency observations from LOFAR were
published. Our aim is to combine this data set with other surveys at higher
frequencies to study the spectral properties of a large sample of radio
sources. Methods. We present a new cross-matching algorithm taking into account
the sizes of the radio sources and apply it to the LoLSS-PR, LoTSS-DR1,
LoTSS-DR2 (all LOFAR), TGSS-ADR1 (GMRT), WENSS (WSRT) and NVSS (VLA)
catalogues. We then study the number of matched counterparts for LoLSS radio
sources and their spectral properties. Results. We find counterparts for 22 607
(89.5%) LoLSS sources. The remaining 2 640 sources (10.5%) are identified
either as an artefact in the LoLSS survey (3.6%) or flagged due to their
closeness to bright sources (6.9%). We find an average spectral index of
α=−0.77±0.18 between LoLSS and NVSS. Between LoLSS and LoTSS-DR2
we find α=−0.71±0.31. The average spectral index is flux density
independent above S54=181 mJy. Comparison of the spectral slopes from
LoLSS--LoTSS-DR2 with LoTSS-DR2--NVSS indicates that the probed population of
radio sources exhibits evidence for a negative spectral curvature.Comment: 13 pages, 22 figures and 2 tables. Accepted for publication in A&