  The object 4C 71.07 is a high-redshift blazar whose spectral energy
distribution shows a prominent big blue bump and a strong Compton dominance. We
present the results of a two-year multiwavelength campaign led by the Whole
Earth Blazar Telescope (WEBT) to study both the quasar core and the beamed jet
of this source. The WEBT data are complemented by ultraviolet and X-ray data
from Swift, and by gamma-ray data by Fermi. The big blue bump is modelled by
using optical and near-infrared mean spectra obtained during the campaign,
together with optical and ultraviolet quasar templates. We give prescriptions
to correct the source photometry in the various bands for the thermal
contribution, in order to derive the non-thermal jet flux. The role of the
intergalactic medium absorption is analysed in both the ultraviolet and X-ray
bands. We provide opacity values to deabsorb ultraviolet data, and derive a
best-guess value for the hydrogen column density through the analysis of X-ray
spectra. We estimate the disc and jet bolometric luminosities, accretion rate,
and black hole mass. Light curves do not show persistent correlations among
flux changes at different frequencies. We study the polarimetric behaviour and
find no correlation between polarisation degree and flux, even when correcting
for the dilution effect of the big blue bump. Similarly, wide rotations of the
electric vector polarisation angle do not seem to be connected with the source
activity.
