FS725 Rubidium Frequency Standard

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 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 of ( -130 dBc/Hz at 10 Hz offset) and one second Allan Variance of (<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.

FS725 Single Sideband Phase Noise

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 1pps input. The relays are SPDT, providing both normally-open and normally-closed contacts.

 

 

 

Phone: (408)744-9040 • Fax: (408)744-9049 • email: info@thinkSRS.com • www.thinkSRS.com

FS725 Rubidium Frequency Standard
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-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 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 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 W
Dimensions	8.5" × 3.5" × 13" (WHL)
Weight	9 lbs.
Warranty	One year parts and labor on defects in materials and workmanship
Phone: (408)744-9040 • Fax: (408)744-9049 • email: info@thinkSRS.com • www.thinkSRS.com