  We try to explain the unusually high far-infrared emission seen by IRAS in
the double-lobed radio-loud quasars 3C47, 3C207 and 3C334. High resolution
cm--mm observations were carried out to determine their radio core spectra,
which are subsequently extrapolated to the far-infrared in order to determine
the strength of the synchrotron far-infrared emission. The extrapolated flux
densities being considerably lower than the observed values, a significant
nonthermal far-infrared component is unlikely in the case of 3C47 and 3C334.
However, this component could be responsible for the far-infrared brightness of
3C207. Our analysis demonstrates that nonthermal emission cannot readily
account for the difference between quasars and radio galaxies in the amount of
their far-infrared luminosity. On the other hand, a significant role for this
mechanism is likely; full sampling of the mm-submm spectral energy
distributions is needed to address the issue quantitatively.
