The Third Cambridge Catalog of Radio Sources (3C), published in 1959, includes northern hemisphere sources detected by the Cambridge Interferometer Radio Telescope at 159MHz. (I've seen an old reference to 2C 273 so perhaps the third catalog preserved the second catalog's numbering.) Updates 3CR and 3CRR, the latter using 178MHz, preserve the "3C" numbering and are commonly cited with the "3C" designation.
Cambridge Catalog of Radio Sources
NRAO Catalog (NRAO)