Rubidium Atomic Frequency Standard (RAFS)
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Frequency Standards High-Performance Space-Qualified Rubidium Atomic Frequency Standard (RAFS) Key Features High-Stability: 2x10-12 at τ = 1 second Low Power: ≤ 14 watts Low Drift: ≤ 5x10-14/day High-Reliability: 700,000 Hr MTBF Fully Space-Qualified Radiation Hardened Negligible Environmental Sensitivities • Small Size: 5.0” x 8.5” x 6.0” • Low Weight: < 14 lbs. • y • • • • • • • • Global Navigation Satellite Systems (GNSS) The Excelitas Rubidium Atomic Frequency Standard (RAFS) is an exceptionally High-Performance and High-Reliability Space-Qualified rubidium (Rb) clock developed for Global Navigational Satellite Systems. It is the highest performance device of this type currently available, combining exceptional stability and low drift with negligible environmental sensitivity, while offering the low size, weight and power advantages of a rubidium frequency standard. The design has been fully documented and qualified for all space requirements, including radiation. The RAFS offers exceptional performance as a precise time and frequency reference for demanding applications. The RAFS employs classical rubidium gas cell atomic frequency standard principles. It utilizes a physics package with a discrete isotopic filter cell for best stability. The relatively large, cool absorption cell and thin film spectral filter provide exceptionally high signal-to-noise ratio and excellent short term stability. Calorimetric Rb lamp process control and screening assures long life. The "natural frequency" output of 13.4 MHz permits the use of a low complexity, single loop design for improved reliability. Operation at low fixed magnetic bias field improves stability and reduces magnetic and radiation sensitivity. An integral baseplate temperature controller greatly reduces the overall temperature sensitivity by utilizing a thermal insulator that can be tailored to meet various panel operating temperatures. While the RAFS may be operated in air, operating in a vacuum environment that eliminates barometric sensitivity, the extremely low temperature, magnetic, radiation and voltage sensitivities mean that the unit has extremely low sensitivity to all environmental effects, providing a very low flicker floor. The low aging rate of <5x10-14/day is exceptionally smooth and modelable using either a log or diffusion fit to the data. A crystal oscillator at nominal 13.4 MHz produces the output signal via an output amplifier. This RF output path is hardened against transient radiation. The 13.4 MHz crystal oscillator also excites the Rb physics package via a phase modulator and frequency multiplier chain. This produces a discriminator signal that is processed by a servo amplifier to lock the crystal oscillator to the Rb atomic resonance. Temperature controllers, a lamp exciter and a precision C-field source support the operation of the physics package, while a dc/dc converter and linear regulators provide power for the RAFS circuits. An integral controller stabilizes the RAFS baseplate temperature and several analog monitors are available to assess the operation of the unit.

High-Performance Space-Qualified Rubidium Atomic Frequency Standard TABLE 1 Specifications Input Power Warm-up Monitors 28.0 VDC ± 4.0 VDC ≤ 39 W total steady-state with BTC ≤ 14W basic clock at +45°C baseplate ≤ 65 W during warm-up ≤ 1 hour to ± 2x10-10 0 to +5 VDC, 5kΩ source impedance TABLE 2 Baseplate Temperature Controller (BTC) Set-Point Stabilization Factor Thermal Insulator Heater Demand Power TABLE 3 Outputs RF Output Analog Monitors 13.40134393 MHz Sinewave +18 dBm ± 1.5 dB All harmonics ≤ 50 dBc All spurious ≤ -85 dBc (fo ≤ f ≤ 2fo) ≤ -50 dBc (2fo ≤ f ≤ 3fo) Lock, Light, Signal,...

High-Performance Space-Qualified Rubidium Atomic Frequency Standard TABLE 5 Environmental Specifications Operating Temperature Full performance with BTC range between -4°C and +21°C panel temperature. Functional between -20°C to +45°C panel temperature. -34°C to +71°C Sea level to vacuum 12.4g rms, 20 Hz to 2 kHz 1500 g max to 10 kHz -34°C to +71°C 20 g Hardened to withstand natural and manmade space environments, including phasecontinuous operation through transient radiation Per MIL-STD-461E Hardened to withstand ≥ 1000 cycles Storage Temperature Altitude Vibration Pyroshock Thermal...

High-Performance Space-Qualified Rubidium Atomic Frequency Standard FIGURE 2 Block Diagram/Mechanical About Excelitas Technologies Excelitas Technologies is a global technology leader focused on delivering innovative, customized solutions to meet the lighting, detection, energetic, frequency standards and high-reliability power needs of OEM customers. From aerospace and defense applications to industrial, safety and security, medical lighting, analytical instrumentation, and clinical diagnostics, Excelitas Technologies is committed to enabling our customers’ success in their specialty...