A nineteen-year catalog of observations collected by the Universities of Florida and Texas has permitted detailed comparison of Jovian source characteristics at 10 frequencies from 5.6 to 30 MHz. The spectral morphology of Jupiter's decameter wavelength radio sources was studied by means of high-resolution histograms of occurrence probability for intervals as small as 2¿ in Jovian system III longitude and the departure of Io from superior geocentric conjunction. Longitude histograms clearly exhibit a substantial shift in the source A and source B positions between 15 and 10 MHz. Similar diagrams isolate the dependence of each source on the position of Io, illustrating changes with frequency in the structures and sizes of the main probability maxima and in the positions of surrounding secondary peaks. Individual frequency probability histograms for both longitude and Io phase reveal new phenomena, such as a bridge of radiation through source B longitudes connecting sources A and C at 15 MHz and spectral modification of portions of the Io-related source B peak.