Ferrite loaded nonlinear transmission lines (NLTLs) are able to act as high power microwave sources, utilizing the nonlinearities present in ferrimagnetic materials and the excitation of damped gyromagnetic precession at high incident power levels. Ferrimagnetic properties depend greatly on operating temperatures; therefore, there exists a need to know the ideal temperature at which to operate ferrite loaded NLTLs. Ferrites are chilled or heated to a certain temperature for a time suitable to allow internal ferrite temperature uniformity. Experimental temperatures ranged from approximately -20 °C up to 150 °C, which is slightly above the Curie temperature of the loaded ferrites. This temperature range allows observation of precession dependence on temperature while maintaining ferrimagnetic properties and a single look at the behavior outside the ferrimagnetic regime. Above the Curie temperature the loaded ferrites become paramagnetic and lose ferrimagnetic properties. The design, testing, and results are detailed for an NLTL measuring 0.3 m length and ferrite inner and outer diameters of 3 mm and 6 mm respectively. Figures comparing output waveforms at different temperatures, output power versus temperature, and output frequency versus temperature are shown.