The APX-REF400 Precision GNSS Timing Reference is a high-precision satellite-referenced frequency and time reference platform combining a rubidium atomic clock with a high-precision timing receiver.
The system uses advanced frequency measurement and disciplining technology to continuously measure and calibrate the rubidium oscillator against the satellite reference. This enables the internal frequency reference to achieve frequency stability of up to 5 × 10⁻¹⁴ at 10,000 seconds, providing a high-performance frequency standard without requiring periodic manual calibration.
In addition to precision frequency generation, APX-REF400 provides a reproducible UTC time reference. Its internally disciplined 10 MHz reference is divided to generate the 1PPS output, reducing the influence of short-term random variations in the satellite 1PPS signal and providing a more stable time reference.
APX-REF400 is designed for applications requiring high-precision time and frequency references, including scientific research, satellite communications, astronomy, physics experiments, precision measurement, ranging systems, and distributed measurement systems.
Key Features
- High-precision rubidium atomic clock reference
- Satellite-referenced frequency disciplining
- Multi-mode satellite reference architecture
- GNSS synchronization accuracy of <20 ns="" rms="">
- Frequency stability up to 5 × 10⁻¹⁴ at 10,000 s
- Automatic transition between disciplining and holdover modes
- Intelligent learning of rubidium oscillator drift characteristics
- Internal memory for learned oscillator parameters
- Automatic reference-source status evaluation
- Supports external frequency and time references
- Manual selection between internal and external references
- Supports multiple frequency outputs including 10 MHz, 10.23 MHz and 100 MHz
- Adjustable pulse output with high phase-setting resolution
- 1PPS synchronization accuracy of <20 ns="">
- 1PPS holdover accuracy of <30 ns="">under the specified test condition
- Optional BDS-B3, PTP, B-code and TOD inputs
- Optional NTP and PTP timing outputs
- Standard 19-inch 2U rack-mount chassis
Precision Rubidium Frequency Reference
APX-REF400 integrates a standard-grade rubidium atomic clock with a high-precision satellite timing receiver.
During normal operation, the satellite reference disciplines the rubidium oscillator. The system continuously measures the frequency behavior of the oscillator and applies correction parameters to maintain the output frequency relative to the satellite reference.
The system can also learn the oscillator's drift characteristics during operation. These learned parameters are stored in onboard memory and can be used to support stable operation when the external reference becomes unavailable.
This architecture provides both a precision frequency standard and a reproducible UTC time reference.
High-Stability Frequency Output
The internal disciplined 10 MHz reference is used as the basis for generating the system's timing outputs.
Standard frequency outputs include:
Additional output frequencies can be provided as optional configurations.
Frequency Output Specifications
| Parameter | Specification |
|---|
| Output waveform | Sine wave, bipolar |
| Output level | 8 dBm ±2 dB |
| Output impedance | 50 Ω |
| Frequency accuracy | <3> |
| Frequency stability @ 1 s | ≤5 × 10⁻¹² |
| Frequency stability @ 10,000 s | ≤5 × 10⁻¹⁴ |
| Spurious | −70 dBc |
| Harmonics | −40 dBc |
The phase-noise characteristics are configuration-dependent according to the selected reference and output configuration.
GNSS Reference Input
APX-REF400 uses a satellite timing receiver as the primary external reference.
Standard Satellite Antenna Input
- 1 × SMA-K interface
- GPS L1
- BeiDou B1
- +5 V DC antenna power
- Timing accuracy: <20 ns="" rms="">
- Positioning accuracy: 10 m RMS
- 32 channels
- Cold start: <29 s="">
- Hot start: <1 s="">
The system uses satellite reference information to discipline the internal rubidium frequency standard and establish the system time reference.
Intelligent Disciplining and Holdover
APX-REF400 incorporates an intelligent operating strategy for reference management.
During normal disciplining operation, the system continuously learns the drift characteristics of the internal rubidium oscillator and stores relevant parameters in onboard memory.
The system can intelligently determine the stability of the external satellite reference and switch between operating modes according to the available reference condition.
The operating modes include:
Disciplining Mode
The internal rubidium oscillator is continuously disciplined against the external satellite reference.
Holdover Mode
When the external reference becomes unavailable, the system can continue to provide time and frequency outputs using the historical performance characteristics of the internal oscillator.
Reference Switching
The system supports multiple timing references and can select an alternative external frequency reference when the primary reference becomes unstable or unavailable.
This architecture allows the equipment to continue providing a high-quality time and frequency reference during temporary loss of the primary reference.
External Timing References
APX-REF400 supports external frequency and time reference inputs.
Standard reference interfaces include:
- External frequency reference input
- External time reference input
Optional input configurations include:
- BDS-B3
- PTP / IN
- B-code / IN
- TOD / IN
The system also supports manual selection between internal and external frequency and time references.
1PPS Output
The 1PPS output is generated from the internally disciplined frequency reference.
Instead of directly reproducing short-term variations of the satellite 1PPS signal, the system derives the pulse timing from the disciplined internal frequency reference, providing a stable time output.
1PPS Specifications
| Parameter | Specification |
|---|
| Waveform | 1PPS pulse |
| Frequency | 1–200 Hz |
| Synchronization accuracy | <20 ns=""> |
| Holdover accuracy | <30 ns=""> |
| Holdover test condition | 30-day synchronization, 24-hour holdover |
| Pulse width | 2 ms |
| Rise/fall time | ≤1 ns |
The configurable pulse frequency allows the system to support different timing and measurement requirements.
Optional Frequency Outputs
In addition to the standard 10 MHz, 10.23 MHz and 100 MHz outputs, optional frequency outputs include:
- 1 MHz
- 5 MHz
- 20 MHz
- 40 MHz
- Other frequency configurations according to system requirements
Optional Pulse Outputs
Optional pulse timing outputs include:
The phase of the pulse output can be configured with high adjustment resolution.
Optional NTP and PTP Outputs
For applications requiring both precision frequency reference and network time distribution, APX-REF400 can be configured with:
- NTP timing output
- PTP timing output
This allows the precision reference platform to serve as a timing source for connected network equipment and distributed timing systems.
Scientific and Measurement Applications
APX-REF400 is designed for environments where stable and accurate time and frequency references are important to measurement or observation accuracy.
Typical applications include:
Scientific Research
Provides a precision time and frequency reference for high-accuracy experiments, measurements, and data acquisition.
Astronomy
Provides a stable timing reference for astronomical observation and measurement systems.
Physics Research
Supports experiments requiring highly stable and traceable time and frequency references.
Satellite Communications
Provides a precision frequency and time reference for satellite communication systems.
Ranging Systems
The synchronized time reference can provide trigger signals for ranging and measurement equipment.
Multi-Channel Measurement
A common time reference can be used for simultaneous acquisition of multiple measurement signals.
Physical and Environmental Specifications
| Parameter | Specification |
|---|
| Chassis | Standard 19-inch 2U |
| Weight | <50 kg=""> |
| Power supply | 220 VAC |
| Operating temperature | 0°C to +50°C |
| Storage temperature | −40°C to +85°C |
| Humidity | 95% RH, non-condensing |
| Power consumption | <120 w=""> |
Standard Package
The standard configuration includes:
- APX-REF400 timing and frequency reference unit
- Coaxial cable
- GNSS antenna
- Mounting brackets
- Power cable
- User documentation
- Certificate / warranty documentation
- Test report
- Instrument case
Website Category Positioning
Primary Category: Precision Timing References
Product Series: APX-REF Series
Product Positioning: Precision GNSS-Disciplined Rubidium Timing Reference
APX-REF400 is positioned as a high-performance precision time and frequency reference within the APEX timing portfolio. It combines GNSS satellite synchronization, a rubidium atomic clock, intelligent frequency disciplining, and high-performance holdover to provide a stable reference for demanding measurement, scientific, communications, and timing applications.
Applications
Scientific Research
Precision time and frequency reference for experimental and measurement systems.
Astronomy
Stable timing for observation, acquisition, and precision measurement applications.
Physics & Precision Measurement
Reference timing for high-accuracy experiments and synchronized data acquisition.
Satellite Communications
Precision frequency and time reference for satellite communication infrastructure.
Ranging Systems
Stable time reference and configurable pulse outputs for ranging and measurement systems.
Distributed Measurement
Common time and frequency reference for multi-channel measurement and acquisition equipment.
Precision Timing Infrastructure
High-stability frequency and UTC-referenced timing for specialized synchronization systems.
