  We investigate the correlation between the accretion disk (UV) luminosity and
the radio core emission of a quasar sample. In a radio/$L_{\rm disk}$ plot we
find the quasars to be separated into four classes: core dominated quasars
(CDQ), lobe dominated quasars (LDQ), radio-intermediate quasars (RIQ) and radio
weak quasars. In general the radio core emission scales with the disk
luminosity, especially in the radio weak quasars. This shows that radio and UV
emission have a common energy source and that the difference between radio loud
and radio weak is established already on the parsec scale. We investigate the
possibility that radio jets are responsible for the radio core emission in
radio loud and radio weak quasars. Comparing our data with a simple jet
emission model that takes the limits imposed by energy and mass conservation in
a coupled jet-disk system into account, we find that radio loud jets carry a
total power $Q_{\rm jet}$ that is at least 1/3 of the observed disk luminosity
$L_{\rm disk}$. For the electron population one is forced to postulate an
efficient process producing a large number of pairs and/or injecting electrons
with a distribution with low-energy cut-off around 50 MeV -- secondary pair
production in hadronic cascades could be such a process. The bulk Lorentz
factor of the jet is limited to a narrow region ($3\la\gamma_{\rm j}\la10$)).
The radio emission of radio weak quasars can be explained with exactly the same
parameters for a powerful relativistic jet if secondary pair production, as
suggested for radio loud jets, is inhibited. There is evidence that RIQ are the
relativistically boosted population of radio weak quasar jets. We can estimate
the hidden disk luminosity of FR II galaxies and find that this is consistent
with FRII being misdirected quasars.
