A long-term decadal scale variation of Jovian decimetric radio emission has been reported that could indicate intrinsic time variability in the Jovian radiation belts and/or magnetic field. However, the strong beaming of the radition by trapped relativistic electrons in the complex Jovian magnetic field can also result in apparent decimetric radiation changes due to the evolving viewing geometry of Jupiter during its 11.9-year orbit. To investigate this problem, radial diffusion models of Jovian trapped electron fluxes at relevant energies are first constructed to simulate possible causes of intrinsic variations. Results indicate several inconsistencies with observations. For example, an increase in diffusion rate with other parameters held constant results in an inward displacement of the peak emission radial distance that is not observed. Second, effects of viewing geometry changes are examined. The possible importance of such effects is suggested by a correlation between the total decimetric radio flux and the Jovigraphic latitude of the Earth, DE, which varies between -3.3¿ and +3.3¿ during one Jovian orbital period. Because the Jovian central meridian longitudes where the magnetic latitude passes through zero during a given Jovian rotation change substantially with DE and since significant longitudinal asymmetries exist in both the volume emissivity and the latitudinal profile of the beam, the total intensity should be at least a partial function of DE. Thus variations of viewing geometry associated with Jupiter's orbital motion should be more fully accounted for if long-term intrinsic variability of Jovian synchrotron radiation is to be unambiguously detected. ¿ American Geophysical Union 1993