SRS SIM940 Rubidium Frequency Standard
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- Three 10 MHz outputs
- 1 pps input and output for GPS synchronization
- 20 year aging less than 0.005 ppm
- Ultra-low phase noise
- Remote interface
Lambda Exclusive Promotion:
Additional 12 months warranty for free (2 years total) via our UK Service Centre.
The Stanford Research Systems 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 SRS 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.
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.
| 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 SIM940 datasheet 
