The Model 683C Sweep Oscillator is one of several Electronic Sweep Oscillators which cover major microwave bands. Sweep oscillators are used as signal sources for a wide variety of laboratory and production tests. They provide a high-level relatively constant-amplitude signal that can be rapidly changed in frequency. Thus they permit the characteristics of microwave systems or components to be quickly checked over an entire band of frequencies. The Model 683C Sweep Oscillator covers the complete S band from 2 to 4 kmc (gc) and uses a backward wave oscillator (bwo) tube to generate the rf signal. The bwo tube has several advantages over previously used klystron type microwave oscillator tubes when used in sweep sources.