The Efratom Model FRS Rubidium Standard is a sub-miniature, atomic resonance-controlled Oscillator that provides an extremely stable signal of 2.048 MHz TTL, 5 MHz, or 10 MHz (TTL or sinusoidal). The FRS C is designed for instruments and equipment requiring an extremely stable and precise frequency operating in commercial/industrial environmental conditions. The FRS N is designed primarily for use in high-performance communication and Navigation system with more stringent environmental conditions.