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 systems with more stringent environmental conditions.