Cesium Beam Primary Frequency Standard
A Hybridized High-Reliability Militarized Cesium Beam Frequency Standard
Military Nomenclature: Master Regulating
Clock 0-1824A/U Per MIL-F-28811A

Model FE-5440A, Option FHA

Easy to use, simple to operate
Extraordinary accuracy and long-term stability
SC cut quartz crystal to provide stable operation under dynamic environment
Front panel "C" Field Adjustment
Hybrid electronics for improved reliability, smaller size, lower power consumption
Rugged militarized design
May be synchronized externally to any second of time with a simple control button
Fully interchangeable modules

Download FE-5440A PDF Datasheet


FE-5440A front and rear view

Function Description   Technical Characteristics

The Cesium Beam Primary Frequency Standard is a rugged, compact, militarized, hybridized, solid-state, Atomic Frequency Standard and Real-Time-Of-Day Clock, which provides

• Standard and sinusoidal output frequencies of 5 MHz, 1 MHz and 100 kHz accurate to ±5x10-12 with a long-term stablity of ±1x10-11.

• Timing information in hours, minutes and seconds, in the form of a direct real-time LED display Time-Of-Day Clock, and 1 PPS and PPM outputs for driving external clocks.

The Standard owes its exceptional accuracy and stability to a unique frequency comparison-and-control system, in which a cesium atom (Cs133) is used to stabilize the output frequency of a precision voltage-controlled quartz crystal oscillator using an SC cut crystal to provide improved performance under dynamic environments. The oscillator output is multiplied and drives the cesium tube.

The signal induces transitions from one hyperfine energy level to another, and those atoms which have undergone this transition are detected by a hot wire ionizer and electron multiplier. The output of the electron multiplier is fed back through an oscillator control circuit to correct the oscillator frequency, maintaining the Standard's accuracy.

Meters and Displays
Major circuit functions and signal levels are metered via a front panel circuit switch and meter in combination, providing a convenient means for determining the operational status of major circuits. Operating status and alarm LED displays indicate operational status of the primary and secondary loops.

Compact, Transportable
The Standard may be transported, used as a bench-mounted unit or rack-mounted by using the four mounting screws on its front panel.

Three Power Sources
The Standard may be operated from three power sources:
• First Priority—115 or 230 Vac, 47 to 400 Hz, single-phase.

• Second Priority—External 22 to 30 Vdc
• Third Priority—Internal battery supply.
Simultaneous connection of ac and dc power source inputs can be made.

Front panel indicators advise of input power availability, power source in use, and changing status of the internal battery supply.

In the event of a power failure in any mode, automatic transition between power sources takes place without any effect or perturbation of time and frequency accuracy.

Modular Construction
The standard utilizes modular construction for ease of maintenance and maximum operational reliability. All modules are removeable, minimizing downtime should a module require replacement. Most modules may be easily replaced in only a few minutes. All modules are interchangeable, minimizing spare module inventories.

Accuracy ±3x10-11, maintained over a temperature range of –28°C to +65°C and magnetic fields up to 0.2 millitesla (2 gauss) peak.
Reproducibility ±1x10-11


Stability (5 MHz)
See Figure 1
Output Voltage 1.0 to 1.5 Vrms into 50 ohms.
Voltage Required 115 or 230 Vac 10%, single phase. 47 to 100 Hz; or 22 to 30 Vdc.
Warm-Up Time 20 min.from –28°C when operated from ac line
Operating Temperature Range –28°C to + 65°C