FS725 Stanford Research Standard Used

Output

• Output frequencies: 10 MHz sine, 5 MHz sine, 10 μs wide 1 pps pulse
• Amplitude: 0.5 Vrms, ±10 %
• 1 pps pulse amplitude: 2.5 V into 50 Ω, 5 V into High-Z 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
• 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 RS-232)
• Warm-up time: <6 minutes (time to lock); <7 minutes (time to 1 × 10^–9)

Front-Panel Indicators (Green LEDs)

• Power: “On” when AC power is applied
• Locked: “On” when frequency is locked to Rb
• 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 1 pps input
• Receive: Blinks when RS-232 characters are received by FS725
• Send: Blinks when RS-232 characters are sent by FS725

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: Two 50 Ω isolated sine outputs
• 5 MHz output: One 50 Ω sine output
• 1 pps output: One 50 Ω pulse output
• Optional outputs: Each option board provides four 10 MHz, one 5 MHz, and one 1 pps outputs. Up to 3 boards can be installed.
• Alarm relays: Max. current, 3 A. SPDT, normally open or normally closed. May be wired in parallel with other relays to “wire-or” a single alarm.
• Rb lock: Relay status matches the front-panel “Locked” LED.
• 1 pps: Relay status matches the front-panel “1 pps sync” LED.
• RS-232: 9-pin connector configured as DCE,9600 baud. Windows RbMon software is provided.

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 (1 Gauss field reversal)
• Relative humidity: 95 % (non-condensing)

General

• AC power: 90 to 132 VAC or 175 to 264 VAC, 47 to 63 Hz, 50 W
• Dimensions: 8.5" × 3.5" × 13" (WHL)

The Stanford Research Systems FS725 integrates a rubidium oscillator (SRS model PRS10), a low-noise AC power supply, and distribution amplifiers in a compact, half-width 2U chassis. 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 FS725 is an ideal instrument for calibration and R&D laboratories, or any application requiring a precision frequency standard.

There are two 10 MHz and one 5 MHz outputs with exceptionally low phase noise (–130 dBc/Hz at 10 Hz offset) and one second Allan variance (<2 × 10^–11). The FS725 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.

Up to three internal distribution modules can be added to the FS725. Each module has four 10 MHz outputs, one 5 MHz output, and one 1 pps output, all with the same low phase noise, harmonic distortion and jitter.

An RS-232 interface allows direct communication with the rubidium oscillator. Using the provided Windows software, you can easily monitor and control 1 pps timing, and determine the instrument’s operational status.

There are two alarm relays that indicate the status of the rubidium oscillator lock state and synchronization to an external 1 pps input. The relays are SPDT, providing both normally-open and normally-closed contacts.