A superheterodyne emitter-receiver system is described which may be used either as a swept frequency or a cavity locked coherent microwave source in the full x band. Constructional details are given and information about spectral purity (Allan variance) and longterm stability for both modes of operation are reported. The performance of the system is demonstrated by its use as a high sensitivity high resolution Stark or source modulated microwave gas spectrometer and as an ESR spectrometer.