Rubidium Atomic Frequency Standard

Model FE-5680A

Extremely low silhouette: less than 1.0 inch
Stability over temperature: 5x10-11
Digitally programmable to 1x10-13
Frequency: 1 Hz to 20 MHz *
Fast Warm-up: <5 min.
Stability: To 5x10-12/ to 2x10-10/year

Function Description   Technical Characteristics

The Fe-5680A Rb frequency standard is 3.5x5.1 inches, a design suited to PC board slot mounted applications. A simplified functional block diagram is shown in Figure 3.

Many commercial applications for precision frequency standards demand performance over an expended temperature range. Often frequency variation with temperature is the performance range. Often frequency variation with temperature is the performance-limiting feature of these devices for CDMA holdover applications. The two products described in this paper have both been designed to operate over extended temperature ranges while guaranteeing a frequency variation of less than 1E-10. The FE-5680A operates at any temperature between -10 and +60 deg. C, a temperature range required for indoor rack-mounted telecommunication hardware with limited air flow. The FE-5652A operates at any temperature between -40 and +85 deg. C, a temperature range required for outdoor, limited access, low maintenance telecommunication hardware.

Frequency variations due to ambient temperature variations can easily swamp other sources of instability for a Rb frequency standard operating in a real life environment. Therefore, special attention was given to frequency stability vs. temperature in these designs. Figure 5 and 5 show typical performance data for FE-5680A and FE-5652A. Rb standards over the ambient temperature range. In addition to the information provided by these plots, it is useful to understand the distribution of performance associated with a production lot of these devices. Table 2 provides this information.

The information in this table shows that the mean total frequency deviation over temperature is very small. What this really means is that the frequency deviation is equally likely to be positive or negative. The standard deviation values give an indication of the range of deviations to be expected amongst production devices.

Allan deviation stability data for the FE 5680A Rb standards are shown in Figure 7. The measurements used to derive the Allan deviation were all made at 25 deg. C. It is of interest to note that the result for SN 4005 is significantly improved by comparing it to another Rb standard (SN 5359) rather than a Cs reference. This indicates that the result is limited by the stability of the Cs reference.


Performance results for two new Rubidium frequency standard products have been reported. These products continue the trend toward small, robust, high-performance atomic frequency standards capable of operating in harsh non-laboratory environments, yet providing stabilities approaching those measured under controlled laboratory conditions. These devices are well suited to the demands of the telecommunications industry for the performance-limiting feature of these devices for CDMA increasingly precise time and frequency references capable of operating unattended in harsh environments.

Download PDF Datasheet

Frequency 10 MHz (factory settable 1 Hz to 20 MHz)
Settability (frequency) ±1 x 10-11
Adjustmant Range 2 x 10-9
Long Term Stability 2 x 10-9/year
2 x 10-11/day
Short Term Stability Averaging Time (SEC) 1.4 x 10-11
Warm-up Time <5 min. to lock
Retrace 5 x 10-11
Output Voltage 0.5 V RMS into 50 ohm sinewave
Harmonic Distortion 30dB
Spurs 60dB

Phase Noise
@ 10MHz

Hz dBc
10 100
100 125
1000 145
Frequency vs Temp 3 x 10-10 (-5°C to +50°C)
Power Consumption (25íC) 11 W (steady state)
32 W (peak)╩╩
Voltage Required 15 to 18 V @700mA
Size 0.98" x 3.4" x 4.92"
Weight 15.3 oz.
-5íC to +50íC