AccuBeat Ltd.

AR133A-00
The AR133A is AccuBeat’s new generation multifunctional Rubidium Frequency Standard.  It is one of the smallest atomic standards available today, where the accuracy and stability are derived from a quantum  transition that occurs in a free rubidium atom. The unit utilizes a unique advanced technology, which allows reducing the unit’s size without sacrificing performance.
The AR133A is comprised of a unique DFLL (Digital Frequency Lock Loop) where a high performance crystal oscillator is locked to the rubidium atomic line using an embedded microprocessor and a special patented algorithm.
The algorithm optimizes the performance vs. external disturbances, improves temperature stability, and enables very fine digital frequency control.

AR133A-03
The AR133A-03 is a ruggedized version of Rubidium Frequency Standard model AR133A which is designed for airborne applications. A vibration isolator included in the AR133A-03 enables the unit to maintain high frequency stability and accuracy in vibration environments such as airborne platforms.
The unit features very fast warm-up and could be disciplined to an external 1PPS from GPS or other sources. It is one of the smallest, high performance disciplined rubidium frequency standards available today. The AR133A is comprised of a unique DFLL (Digital Frequency Lock Loop) where a high performance crystal oscillator is locked to the rubidium atomic line using an embedded microprocessor and a special patented algorithm.

AR61A – 08
AR61A-08 is a very high performance Rubidium Frequency Standard, designed to operate reliably in demanding application and harsh environment. It performs over a very wide temperature range, provides high stability, even under sever vibration and very fast warm-up, even at -54°C. The unit meets or exceeds the most severe military requirements. This rugged unit is especially useful in airborne applications as well as mobile ground operation. The AR61A-08 also includes a microprocessor, which optimizes its performance vs. external disturbances. It has a unique holdover mode, which keeps the internal OCXO running with the last memorized frequency when lock is lost. In addition, a built in synthesizer allows a very fine digital frequency control over a wide range.

AR51A-09
The AR51A-09 unit is a compact GPS-Disciplined Rubidium Clock, which offers an excellent stability and accuracy. The unit includes a Rubidium-Atomic-Standard, which is phase-locked to the disciplining source (like GPS or other external inputs).
All outputs are derived from the Rubidium-Atomic-Standard and maintain highly accurate time and frequency even when GPS reception interrupted.
The AR51A-09 includes Time of Day (TOD) inputs and outputs. The standard unit include several Have Quick (ICD-GPS-060) Time Code outputs, followed by several (more than 20) 1PPS outputs (PTTI ICD-GPS-060, TTL and RS-422 formats) for accurate timing which is essential for secure radio communication applications.
The standard unit includes also Have Quick (ICD-GPS-060) Time Code input for initial time loading followed by 1PPS input for the 1PPS timing synchronization, when the GPS signal is not available.

AR51A-07
The AR51A-07 unit is an industrial low profile GPS-Disciplined Rubidium Clock which offers an excellent stability and accuracy. The unit includes a Rubidium-Atomic-Standard which is phase-locked to the GPS or other external inputs. All outputs are derived from the Rubidium-Atomic-Standard and maintain highly accurate time and frequency even when GPS reception is interrupted. When disciplined to GPS the unit provides time accuracy of < 20ns RMS and frequency accuracy better than 2E-12.
The AR51A-07 includes Have Quick (ICD-GPS-060) input and output which is essential for secure radio communication applications. The unit can be remote controlled via MIL-STD-1553RT channel which is required in airborne applications.

AR51A-05
The AR51A-05 offers militarized Rubidium Atomic Clocks, which is synchronized to the Global Positioning System (GPS), thereby providing extremely accurate time & frequency.
The AR51A-05 incorporates numerous features into a single box, including a Rubidium Standard, an internal GPS receiver a Rubidium-GPS DPLL (disciplining) circuit, time codes, multiple outputs. The Rubidium clock is phase locked to the GPS or other external inputs (as a back-up to GPS system). All outputs are derived from the Rubidium clock which maintains time and frequency when GPS or other inputs are interrupted.
The AR51A-05 has been fully qualified for operation in harsh stressed environments on ground mobile, airborne, fighter aircraft, Helicopter and ship borne platforms.

AR51A-08
The AR51A-08 offers militarized Rubidium Atomic Clocks, which is synchronized to the Global Positioning System (GPS), thereby providing extremely accurate time & frequency.
The AR51A-08 incorporates numerous features into a single box, including a Rubidium Standard, an internal GPS receiver a Rubidium-GPS DPLL (disciplining) circuit, time codes, multiple outputs. The Rubidium clock is phase locked to the GPS or other external inputs (as a back-up to GPS system). All outputs are derived from the Rubidium clock which maintains time and frequency when GPS or other inputs are interrupted.
The AR51A-08 has been fully qualified for operation in harsh stressed environments on ground mobile, airborne, fighter aircraft, Helicopter and ship borne platforms.

AR76
The AR76A is a multi-function GPS Disciplined Rubidium Atomic Clock, which provides accurate time & frequency. The AR76A incorporates numerous features into a single box, including a Rubidium Frequency Standard, an internal C/A code 12 channels GPS receiver, and an input from external 1PPS / frequency.
The various options of the unit include a variety of different frequencies and several Time Codes outputs. The Rubidium Standard functions as a local oscillator and is phase-locked to the GPS or to external inputs. All outputs are derived from the Rubidium Clock, which maintains accurate time and frequency when GPS or other inputs are interrupted. For low cost applications an Oven Control Crystal Oscillator (OCXO) is offered instead of Rubidium Frequency Standard.

AR77
The AR77A is a multi-function GPS Disciplined Rubidium Atomic Clock, which provides accurate time & frequency. The AR77A incorporates numerous features into a single box, including a Rubidium Frequency Standard, an internal C/A code 12 channels GPS receiver (or P(Y) code GPS receiver. The GPS receiver must be supplied by user) and an input from external 1PPS / frequency.
The various options of the unit include a variety of different frequencies and several Time Codes outputs. The Rubidium Standard functions as a local oscillator and is phase-locked to the GPS or to external inputs. All outputs are derived from the Rubidium Clock, which maintains accurate time and frequency when GPS or other inputs are interrupted. For low cost applications an Oven Control Crystal Oscillator (OCXO) is offered instead of Rubidium Frequency Standard.

AR50A
The AR50A is a portable case of GPS-Discipline Rubidium Atomic Clock model AR51A-07, which is designated to disseminate frequency and time (TOD – Time of Day).
As an example, the portable clock can be used for time & frequency dissemination in scenarios when the GPS signal is absent or jammed.
The AR50A-03 loads accurate time & frequency from an external source, maintains it on the go and disseminates the accurate time & frequency to the destination clock. The unit includes a set of auxiliary cables and power supplies to enable working with 110V / 220VAC, 12V / 28VDC and cables for dissemination the signals.

AccuBeat specializes in providing customers fully customized solutions, designed to meet the most demanding specifications and requirements. AccuBeat’s highly professional and experienced team of managers, PhDs, engineers and technicians works closely with customers applying years of know-how and experience to the development and manufacture of the most demanding and most accurate Rubidium timing and frequency centers and solutions.

What is an Atomic Clock?
An atomic clock is the most accurate man-made time device. In an atomic clockthe atom is the pendulum of the clock. When an electron inside an atom transitsbetween two energy levels, it either emits or absorbs an energy quantum of aprecise frequency, which is related to the energy difference between the twoatomic levels (according to Planck’s formula E = hv).Thus it creates an atomic oscillator.

What Makes Atomic Clocks Accurate?
Four major facts underlie the accuracy of Atomic clocks:

• The output frequency is locked to the energy level difference of free atoms.
• The atoms are isolated from their surroundings (minimum interaction/ collisions with other atoms, photons, fields, etc.)
• Long interrogation time reduces frequency uncertainty (by Heisenberg principle: (f ~ 1/(t).
• The atoms' thermal motion is reduced as much as possible (eliminating Doppler shift of the 1st and 2nd order).

What is a Rubidium Atomic Clock?
A rubidium clock is an atomic clock which uses rubidium atoms and an “optical pumping” technique to measure the atomic transition frequency. A rubidium Atomic clock includes 87Rb isotope confined in a vapor cell.
The atoms are excited to a high energy level (in figure #1) by light emitted by other 87Rb atoms. The light is filtered to achieve the required wavelength,thereby increasing the population of level 2 compare to level 1.

An injected microwave frequency of ~6.84GHz induces transition from level 2 to level 1 increasing the number of atoms in level 1, and yielding more absorption of light. A photodiode detects the reduction in the light intensity. This reduction occurs only when the injected microwave frequency equals precisely the transition frequency of the atoms. The injected frequency is derived from a crystal oscillator. The photodiode detection signal is then used to tune the crystal oscillator frequency. In other words, the crystal oscillator frequency is locked to the frequency of the waves emitted by the atoms.

• Light from a 87Rb lamp contains both 3-1 and 2-1 lines.
• A 85Rb cell filters the 2-1 line out, and transmits the 3-1 line only.
• The filtered light “optically pumps” the 87Rb atoms in the resonance
• cell from level 1 to 3.
• A microwave signal at a frequency of 6.84 GHz is injected into the cell and induces transition from level 2 to 1.
• When the injected wave frequency matches the difference of the 2-1 line, the
• Photo-diode detects a reduction in the intensity of the transmitted light.

AccuBeat's Digital Frequency Locked Loop
AccuBeat's rubidium frequency standards use a unique Digital FrequencyLocked Loop (DFLL) to implement the disciplining of the crystal oscillator tothe atomic resonance frequency. A microprocessor is embedded in the DFLL, witha unique patented algorithm. This algorithm reduces the sensitivity to externaldisturbances, allows easy lock at start, and enables the implementation of aunique hold-over mode. This keeps the internal oscillator running with the lastmemorized frequency when the lock is lost. These features make the rubidiumfrequency standard a very smart clock.
In addition, the microprocessor enables user access to internal parameters allowingvery fine control of the digital frequency over a wide range.

What is GPS?
The Global positioning System (GPS), operated by the USDoD, is comprised of a total of 24 satellites orbiting round Earth in 6 different planes. There are 4 satellites in each plane, each at 20,200 km altitude and 55 degree inclinations (see Figure 1).

A GPS receiver receives at least 4 signals from 4 satellites. The receiver can then resolve it’s exact position as well as its exact time from the time of arrival of the 4 signals (see Figure 2). A GPS receiver can provide global, all-weather, 24-hour, real-time, accurate navigation and time reference to an unlimited number of users. However, GPS receivers are sensitive to external effects, such as extreme weather, intentional or unintentional jamming. In addition the U.S. government has the capability of blocking the signal in designated areas.

A GPS receiver outputs four-dimensional data, which are comprised of location (position) and time. Part of the time signal is a 1 pulse per second (1 PPS) signal that may be considered to be an accurate 1 Hz frequency source. The short-term stability of the 1 PPS is not very good due to its relatively high jitter. For example, a jitter of 400 nanoseconds translates into a short-term stability of 4E-7 at an averaging time of 1 second, which is rather poor. However, in the long term, the stability of the 1 PPS tracks the excellent stability of the GPS system (which is comprised of atomic clocks located aboard satellites and in ground stations). For more information on GPS see http://tycho.usno.navy.mil/.

GPS Synchronized Rubidium Clocks
In order to solve the problems of interruption in the GPS reception and the jittering of the GPS signal, one may use the following technique. A Rubidium Clock is locked via a phase lock loop (PLL) to the 1 PPS signal coming from the GPS receiver. See Figure 3 for a diagram of the PLL. GPS Synchronized Rubidium Clocks combine the superb medium and short-term stability of the RFS with the excellent long term stability of the GPS receiver. In addition, if the GPS reception is interrupted for a short or long period of time, the Rubidium Standard continues to maintain accurate frequency and time.