Images of the six 3C sources, observed in the range 30–80 MHz. The beam sizes are indicated in the bottom left corner. The optical counterparts of the sources are indicated with crosses. The positions of the optical counterparts were taken from Gaia EDR3 (Gaia Collaboration 2021) (3C 196, 3C 298, and 3C 273), Reyes et al. (2008) (3C 295), and Fanti et al. (2011) (3C 273). The brightness scale starts at the 9σ noise level (σ_rms), which is also indicated by the single solid contour. The dashed contours reveal spurious negative emission due to calibration artifacts at the − 3σ_rms level.