Vector network analyzers have been used to determine permittivity and electrical conductivity spectra in the kilohertz to gigahertz range. The objectives of this study were to determine uncertainty in the complex electrical conductivity spectra, and to examine the effect of aggregation on the spectra. Different aggregate sizes of Okoboji silty clay (Fine, smectitic, mesic Cumulic Vertic Endoaquoll), Canisteo (Fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll), and Kennebec silt loam (Fine-silty, mixed, superactive, mesic Cumulic Hapludoll) soils were examined. Each sample was packed into a truncated coaxial cell for measuring the complex electrical conductivity spectra with the vector network analyzer. Each replicate was adjusted to four to six different water contents. Several of the samples had altered spectra shape, especially for aggregates larger than 2 mm of the Okoboji soil. Reasons for the altered shape were related to aggregate / electrode contact, and low density aggregates absorbing water which reduced the connectivity of inter-aggregate water. Problems with connector contact also cause some incorrect data. The 95 percent confidence intervals were very small for parameters fit from the electrical conductivity spectra. The uncertainty due to measurement was a larger source of variability, and sample-to-sample variation contributed the most to variability.