We investigate the correlation between the accretion disk (UV) luminos
ity and the radio core emission of a quasar sample, containing all PG
quasars, also deriving empirical conversion factors from emission line
luminosities to disk luminosities. This method allows us to investiga
te the radio properties of AGN on the absolute scale set by the accret
ion power. In a radio vs. L(disk) plot we find the quasars to be separ
ated into four classes: core dominated quasars (CDQ), lobe dominated q
uasars (LDQ), radio-intermediate quasars (RIQ) and radio weak quasars.
In general the radio core emission scales with the disk luminosity, e
specially in the radio weak quasars. This shows that radio and UV emis
sion have a common energy source and that the difference between radio
loud and radio weak is established already on the parsec scale. We in
vestigate the possibility that radio jets are responsible for the rado
core emission in radio loud and radio weak quasars. Comparing our dat
a with a simple jet emission model that takes the limits imposed by en
ergy and mass conservation in a coupled jet-disk system into account,
we find that radio loud jets carry a total power Q(jet) that is at lea
st 1/3 of the observed disk luminosity L(disk) The strong radio core e
mission in radio loud quasars relative to L(disk) is difficult to expl
ain by normal acceleration of thermal electrons into a non-thermal pow
erlaw distribution. One rather is forced to postulate an efficient pro
cess 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. Width and sh
ape of the UV-radio correlation of LDQ and CDQ limit the parameter ran
ge for the bulk Lorentz factor of the jet to a narrow region (3 less t
han or similar to gamma(j) less than or similar to 10)). The radio emi
ssion of radio weak quasars can be explained with exactly the same par
ameters 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. Our diagram provides also a test for the unification of FR II ra
dio galaxies with quasars as we can estimate the hidden disk luminosit
y of FR II galaxies and find that this is consistent with FRII being m
isdirected quasars.