The Stanford Research Systems FS725 is a high-performance Rubidium Frequency Standard designed for laboratory and precision calibration environments. It offers exceptionally low phase noise, high short-term stability, and integrates standard 10 MHz, 5 MHz, and 1 PPS outputs in a compact half-rack enclosure.
Specifications
General
| Parameter | Value |
|---|---|
| Interfaces | RS-232 (standard), GPIB / IEEE-488 (optional) |
| Display | None (front-panel status LEDs for Lock, 1 PPS, and Output) |
Physical
| Parameter | Value |
|---|---|
| Power Supply | 90 to 132 VAC or 175 to 264 VAC, 47 to 63 Hz, 100 W (warm-up), 30 W (steady-state) |
| Operating Temperature | 0 to 50 °C |
| Dimensions (W×H×D) | 216 × 89 × 330 mm |
| Weight | 4.1 kg |
Frequency and RF Outputs
| Parameter | Value |
|---|---|
| Primary Output Frequencies | 10 MHz, 5 MHz, 1 PPS |
| Number of Standard Outputs | 2 × 10 MHz, 1 × 5 MHz, 1 × 1 PPS |
| Output Level (10 MHz & 5 MHz) | +7 dBm (+/-1 dB) |
| Output Impedance | 50 Ω |
| Output Waveform Type | Sine wave (for 10 MHz and 5 MHz) |
| Harmonics | <-40 dBc |
| Spurious Outputs | <-100 dBc (within 100 kHz of carrier) |
| RF Connector Type | BNC (female, rear panel) |
| Isolation Between Outputs | >100 dB |
| 1PPS Output Pulse Width | 10 µs |
| 1PPS Output Level | TTL (>2.0 V into 50 Ω, >4.0 V into high impedance) |
Frequency Stability and Accuracy
| Parameter | Value |
|---|---|
| Temperature Stability (0 to 50 °C) | <1 × 10^-10 |
| Aging Rate (Monthly) | <5 × 10^-11 |
| Aging Rate (Yearly) | <5 × 10^-10 |
| Allan Deviation (1 s) | <2 × 10^-11 |
| Allan Deviation (10 s) | <1 × 10^-11 |
| Allan Deviation (100 s) | <2 × 10^-12 |
| Retrace (after 24 hours off) | <5 × 10^-11 |
| Warm-up Time to Lock | <6 minutes |
Phase Noise and Jitter
| Parameter | Value |
|---|---|
| Phase Noise @ 1 Hz offset (10 MHz) | <-80 dBc/Hz |
| Phase Noise @ 10 Hz offset (10 MHz) | <-130 dBc/Hz |
| Phase Noise @ 100 Hz offset (10 MHz) | <-140 dBc/Hz |
| Phase Noise @ 1 kHz offset (10 MHz) | <-150 dBc/Hz |
| Phase Noise @ 10 kHz offset (10 MHz) | <-155 dBc/Hz |
Tuning, Disciplining and Synchronization
| Parameter | Value |
|---|---|
| Frequency Tuning Range (via RS-232) | ±2 × 10^-9 |
| Tuning Resolution (via RS-232) | 1 × 10^-12 |
| Electrical Tuning Range (0 to 5 V) | ±2 × 10^-9 |
| Control Voltage Input Range | 0 to 5 VDC |
| 1PPS Input Signal Type | TTL / CMOS compatible |
| 1PPS Input Minimum Pulse Width | 100 ns |
| 1PPS Lock Loop Time Constant Range | 8 minutes to 22 hours |
Interfaces, Monitoring and Control
| Parameter | Value |
|---|---|
| Status Indicators (LEDs) | Lock (green), 1 PPS (green), Output (green) |
| Lock Status Relay Contacts | SPDT contact (closed when locked) |
| Lock Status Open-Collector Output | Active low (conducts when locked) |
| RS-232 Protocol Specifications | 9600 baud, 8 data bits, no parity, 1 stop bit |
Power Specifications
| Parameter | Value |
|---|---|
| Power Consumption (Warm-up) | 100 W |
| Power Consumption (Steady State) | 30 W (at 25 °C ambient) |
| Internal Battery Backup Option | Internal 12 V, 4.5 Ah Gel-cell battery (Option 02) |
| Internal Battery Operating Lifetime | Up to 3.5 hours at 25 °C |
Physical Characteristics
| Parameter | Value |
|---|---|
| Form Factor | 2U high, half-rack width |
| Weight with Battery Option | 7.3 kg |
| Rackmount Compatibility | 19-inch rack-mountable (with optional RM2U rack mount kit) |
Standards and Certifications
| Parameter | Value |
|---|---|
| Calibration Traceability Standard | Traceable to NIST |
Environmental
| Parameter | Value |
|---|---|
| Storage Temperature | -55 °C to +85 °C |
| Operating Humidity | 95% R.H. non-condensing (max) |
Performance
| Parameter | Value |
|---|---|
| Magnetic Field Sensitivity | < 2 × 10^-10 for 1 Gauss field reversal |
| Voltage Sensitivity | < 2 × 10^-11 for a 10% change in line voltage |
| Warm-up Time to 1 × 10^-9 Accuracy | < 10 minutes |
Inputs & Outputs
| Parameter | Value |
|---|---|
| 1PPS Input Impedance | 1 MΩ |
| 1PPS Output Rise Time | < 10 ns |
| Lock Status Relay Rating | 0.5 A @ 120 VAC, 1 A @ 24 VDC |
| Lock Status Open-Collector Rating | 40 VDC maximum voltage, 100 mA maximum sink current |
Options
| Parameter | Value |
|---|---|
| Option 01 Expansion Outputs | Adds 3 × 10 MHz, 1 × 5 MHz, and 1 × 1PPS outputs |
| Option 02 Battery Pack | Internal 12 VDC, 4.5 Ah battery (provides up to 3.5 hours of backup in steady state) |
| Option 01 Maximum Cards | 3 |
| Option 01 Outputs per Card | 5 |
Reliability
| Parameter | Value |
|---|---|
| Expected Rubidium Lamp Lifetime | > 20 years |
1PPS Output
| Parameter | Value |
|---|---|
| 1PPS Output Jitter | < 1 ns (rms, relative to 10 MHz output) |
1PPS Input
| Parameter | Value |
|---|---|
| 1PPS Input Threshold | 1.0 V (nominal) |
Frequency Tuning
| Parameter | Value |
|---|---|
| Analog Tuning Resolution | Digital tuning resolution = 1 × 10^-12 |
| Tuning Voltage Input Impedance | 1 MΩ |
Power
| Parameter | Value |
|---|---|
| AC Input Voltage Range | 90 to 264 VAC |
| AC Input Frequency Range | 47 to 63 Hz |
| DC Input Voltage Range | 22 to 30 VDC |
Power Options
| Parameter | Value |
|---|---|
| Option 02 Battery Capacity | 4.5 Ah |
| Option 02 Battery Voltage | 12 V |
| Option 02 Battery Type | Gel-cell |
Interfaces
| Parameter | Value |
|---|---|
| RS-232 Baud Rate | 9600 bps |
| RS-232 Configuration | 8 data bits, no parity, 1 stop bit (8N1) |
Technology
Rubidium Vapor Frequency Standard
Applications
Precision Frequency Reference and Timekeeping