The 1.4 GHz radio luminosity as a function of K‐z redshift. The lines represent 100 mJy (solid line), 500 mJy (dashed line), and 1 Jy (dot‐dashed line) flux density limits assuming a spectral slope ﹩\alpha =0.4﹩. Squares mark objects with ﹩\alpha ^{1400}_{365}> 0.8﹩, while triangles indicate ﹩\alpha ^{1400}_{365}\leq 0.8﹩. The filled black circle marks the radio luminosity of 3C 257 with spectroscopic redshift ﹩z=2.474﹩.