3C 345 has an active galactic nucleus that has been categorised as a blazar or as a flat spectrum radio quasar.

Within the jet lies a stationary feature ~0.1 mas (with corresponds to about 0.7 pc at the distance of 3C 345) from the core, which has also been found in other blazars.

[9] A long term variability study indicates flares every 3.5 to 4 years, coinciding with the appearance of new features in the radio jets.

[10] It has been suggested that the source of the fluctuation is the presence of a binary supermassive black hole, with the two similar black holes with masses about 7.1×108 M☉ which are separated by around 0.33 pc and orbit each other with a period of 480 years.

The second black hole perturbates the accretion disk, resulting to fluctuations in activity.