Year 2025 One Hertz Challenge: Achieving Precise Time Reference Using a Single Pulse-Per-Second GPS Signal
In an intriguing discovery, electronic engineer Wil Carver found that a Piezo 2940210 10 MHz Voltage-Controlled Crystal Oscillator (VCXO) required an Electronic Frequency Control (EFC) voltage of approximately 4.34 V to achieve the exact 10 MHz output frequency. This deviation from the typical nominal voltage of around 2.5 V was attributed to the age of the oscillator rather than the standard specification.
The EFC voltage plays a crucial role in adjusting the output frequency of VCXOs like the Piezo 2940210. By varying the EFC voltage, the crystal oscillator's frequency subtly shifts, allowing fine frequency control or calibration to maintain precision timing. In most cases, the voltage-to-frequency tuning relationship is linear or near-linear, enabling stable and accurate frequency output.
However, in this instance, the aged oscillator needed a higher EFC voltage to produce the desired output frequency. This tuning allows the oscillator to be disciplined or corrected against reference signals, maintaining an extremely stable and accurate output frequency, a crucial aspect in precision timing applications like GPS-disciplined oscillators.
Here's a summary of the key parameters:
| Parameter | Typical Value / Range | Effect on Frequency | |-------------------------|-----------------------------|---------------------------------| | Nominal EFC Voltage | ~2.5 V (specification) | Midpoint frequency (10 MHz nominal) | | Observed EFC Voltage | ~4.34 V (aged unit) | Required for 10 MHz output | | Frequency Tuning | Controlled by EFC voltage | Frequency increases/decreases with EFC voltage |
For those interested in learning more about this behaviour, a chart illustrating the relationship can be found in the linked notes. Carver's project, titled "Precise Time Ref via 1 Pulse-Per-Second GPS Signal," uses this very oscillator and delves deeper into the research and experiments conducted.
Carver also recommended resources for those interested in stable timing sources, such as "Allan Variance," and learning about timing accuracy, precision, and stability from Tom Van Baak's website, LeapSecond.com. For those specifically interested in OCXOs, Carver suggested checking out XOXO For The OCXO and Inside A Vintage Oven Controlled Crystal Oscillator.
EFC stands for Electronic Frequency Control, and Carver attributed the discrepancy in EFC voltage to the age of the crystal oscillator. If you're having trouble finding specifications for the 2940210, particularly the EFC sensitivity (S), Carver encourages conducting your own experiments and research to fill in the gaps.
The project's GPS Disciplined Oscillator (GPSDO) takes the precise 1 Pulse-Per-Second (PPS) GPS signal and adjusts the 10 MHz crystal oscillator to produce 10,000,000 cycles within one second, ensuring an accurate and stable time reference.
The EFC voltage deviation in the Piezo 2940210, caused by its age, is an example of how technology can evolve with time. This evolution requires a deeper understanding of the hardware's behavior, which can be facilitated through research in the field of science and technology.
