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Rubidium Frequency Standard
SIM940 — 10 MHz rubidium oscillator
  • 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)
  • Remote interface

click to enlarge
SIM940 Rear Panel


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 phase noise (-130 dBc/Hz at 10 Hz offset) and one second Allan variance (<2 × 10-11). 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.

SIM900 Mainframe

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.

Specifications
Output
Output frequencies 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 ±5 × 10-11 (72 hrs. off, then 72 hrs. on)
Settability <5 × 10-12
Trim range ±2 × 10-9 (0 to 5 VDC)
±0.5 ppm (via remote interface)
Warm-up time <6 minutes (time to lock)
<7 minutes (time to 1 × 10-9)
Front-Panel Indicators (LEDs)
Locked Indicates frequency is locked to rubidium
Unlocked Indicates when frequency is unlocked
1 pps input Blinks with each 1 pps reference input applied to rear panel
1 pps sync "On" when 1 pps output is synchronized within ±1 µs of 1pps input
Rear-Panel Connections
Frequency adjust 0 to 5 VDC adjusts frequency by ±0.002 ppm (normally unconnected)
1 pps input One 100 kΩ input. Requires CMOS level pulses (0 to 5 VDC). If an external 1 pps input is applied, lock is maintained between the 1 pps input and 1 pps output with computer adjustable time constant from 8 minutes to 18 hours.
10 MHz outputs Three 50 Ω, isolated 10 MHz sine outputs
1 pps output 50 Ω pulse output
DB15(M) SIM interface (power and communication)
Environmental
Operating temperature +10 °C to +40 °C
Temperature stability Δf/f < ±1 × 10-10 (+10 °C to +40 °C)
Storage temperature -55 °C to +85 °C
Magnetic field Δf/f < 2 × 10-10 for 1 Gauss field reversal
Relative humidity 95 % (non-condensing)
General
Power Power supplied by the SIM900 Mainframe, or optionally by a user-supplied 24 VDC power supply (2.2 A upon start-up, 0.6 A after warm-up period)
Interface Serial via SIM interface, direct to PRS10
Dimensions, weight 3.0" × 3.6" × 7.0" (WHL), 5 lbs.
Warranty One year parts and labor on defects in materials and workmanship



Stanford Research Systems, Inc. • 1290-D Reamwood Ave., Sunnyvale, CA 94089
Phone: (408) 744-9040 • Fax: (408) 744-9049 • email: info@thinkSRS.com • www.thinkSRS.com
© Stanford Research Systems, Inc. 2003