Small Instrumentation Modules SIM940 — 10 MHz rubidium frequency standard · Three 10 MHz outputs · 1 pps input and output for GPS synchronization · 20 year aging less than 0.005 ppm · Ultra-low phase noise (<−130 dBc/Hz at 10 Hz) · 72 hour Stratum 1 level holdover SIM940 10 MHz Rubidium Frequency Standard The SIM940 integrates a rubidium oscillator (SRS model PRS10) into the SIM900 platform. It provides stable and reliable performance with an estimated 20 year aging of less than 5 × 10–9 and a demonstrated rubidium oscillator MTBF of over 200,000 hours. The SIM940 is an ideal instrument for calibration and R&D laboratories or any application requiring a precision frequency standard. There are three 10 MHz outputs with exceptionally low phasenoise and Allan variance. The SIM940 can be phase-locked to an external 1 pps reference (like GPS), providing Stratum 1 performance. A 1 pps output is also provided that has less than 1 ns of jitter and may be set with 1 ns resolution. All functions of the SIM940 can be controlled from a computer via the SIM900 Mainframe. Both RS-232 and GPIB interfaces are supported by the mainframe. Stanford Research Systems

Output frequency 10 MHz sine, 10 µs wide 1 pps pulse Amplitude (±10 %) 0.5 Vrms (+7 dBm) into 50 Ω 1 pps pulse amplitude 2.5 V into 50 Ω, 5 V into high impedance loads Phase noise (SSB) <–130 dBc/Hz (10 Hz) <–140 dBc/Hz (100 Hz) <–150 dBc/Hz (1 kHz) <–155 dBc/Hz (10 kHz) Spurious <–100 dBc (100 kHz BW) Harmonics <–60 dBc Accuracy at shipment ±5 × 10–11 Aging (after 30 days) <5 × 10–11 (monthly) <5 × 10–10 (yearly) 5 × 10–9 (20 years, typ.) Short-term stability (Allan variance) <2 × 10–11 (1 s) <1 × 10–11 (10 s) <2 × 10–12 (100 s) Holdover 72 hour Stratum 1 level (1 × 10-11) Frequency retrace...