Measurements of dielectric relaxations below 1 GHz, and over a wide temperature range, can yield important information on the dynamics of dipoles at both the microscopic and macroscopic levels. Complete characterisations of materials over this region are rare and normally require the integration of several measuring techniques. Although advances in electronics have extended the range of existing techniques, there remains, however, a need for an instrument of superior bandwidth. The present work addresses this problem and is concerned specifically with the methodology and implementation of an automated spectrometer designed to measure the complex permittivity of solids over 13 decades of frequency (between 10−5 Hz and 108 Hz) and at temperatures between -185 °C and +600 °C. Following reviews of current theory and experimental methods, the design and operational criteria of the spectrometer are discussed in principle and in detail. The structure of the operating software is described and examples of algorithms are given. The successful operation of the spectrometer is demonstrated by experiment, including isothermal investigations of the dielectric behaviour of poly(methylmethacrylate) at 35 °C and low density poly(ethylene) at 30 °C.