  The jets of powerful blazars propagate within regions relatively dense of
radiation produced externally to the jet. This radiation is a key ingredient to
understand the origin of the high energy emission of blazars, from the X-ray to
the gamma-ray energy band. These external radiation fields control the amount
of the inverse Compton radiation with respect to the synchrotron flux.
Therefore the predicted spectral energy distribution (SED) will depend on where
the jet dissipates part of its energy to produce the observed radiation. We
investigate in detail how the SED changes as a function of the location of the
jet dissipation region, by assuming rather "standard" (i.e. "canonical")
prescriptions for the accretion disk and its X-ray corona, the profile of the
jet magnetic field and the external radiation. The magnetic energy density of a
"canonical" jet almost never dominates the radiative cooling of the emitting
electrons, and consequently the inverse Compton flux almost always dominates
the bolometric output. This is more so for large black hole masses. Dissipation
taking place beyond the broad line region is particularly interesting, since it
accounts in a simple way for the largest inverse Compton to synchrotron flux
ratios accompanied by an extremely hard X-ray spectrum. Furthermore it makes
the high power blazars at high redshift useful tools to study the optical to UV
cosmic backgrounds.
