Home > Products > Time & Frequency Instruments > FS725


Rubidium Frequency Standard
FS725 — Benchtop rubidium frequency standard
  • 10 MHz and 5 MHz outputs
  • 20 year aging less than 0.005 ppm
  • Ultra low phase noise (<-130 dBc/Hz at 10 Hz)
  • Built-in distribution amplifiers (up to 22 outputs)
  • 1 pps input and output for GPS synchronization
  • RS-232 computer interface
  • Two status alarm relays

 


The FS725 integrates a rubidium oscillator (SRS model PRS10), a low noise universal 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 two hundred thousand hours.

There are two 10 MHz and one 5 MHz outputs with exceptionally low phase noise of -130 dBc/Hz at 10 Hz offset and low one second Allan Variance of <2 × 10-11. The 1 pps output 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.

In most cases the FS725 will be used as a stand-alone frequency standard due to its extremely low aging. However, it can also be phase-locked to an external 1 pps reference (like GPS) for Stratum 1 performance.

An RS-232 interface allows direct communication with the rubidium oscillator. Using the provided WindowsÒ 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 rubidium oscillator lock state and its synchronization to an external 1pps input. The relays are SPDT providing both normally-open and normally-closed operation.

The FS725 is an ideal instrument for calibration and R&D laboratories, or for any application requiring a precision frequency standard. You can now inexpensively deploy accurate frequency references throughout a facility.

Specifications
Output
Output frequencies 10 MHz sine, 5 MHz sine, 10 µs wide 1 pps pulse
Amplitude 0.5 Vrms, ±10 %, (both 5 MHz and 10 MHz outputs)
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 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 rubidium
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
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 10 MHz sine outputs
5 MHz output One 50 Ω, 5 MHz 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 for 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 watts
Dimensions 8.5" × 3.5" × 13" (WHL)
Weight 9 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