GPS Accuracy Contest in 2025: Achieving Precise Timekeeping Using a Single Pulse-Per-Second GPS Signal
In an intriguing exploration of timing accuracy, Wil Carver, a renowned electronics enthusiast, encountered an unusual finding while working on a project that utilises a Piezo 2940210 10 MHz Voltage-Controlled Crystal Oscillator (VCXO). The VCXO, which is both oven-controlled (OCXO) and voltage-controlled (VCXO), is a common choice for applications requiring stable timing sources.
The project, titled "Precise Time Ref via 1 Pulse-Per-Second GPS Signal," aims to take a precision 1 Pulse-Per-Second (PPS) GPS signal and adjust the 10 MHz crystal oscillator to produce 10,000,000 cycles within one second. However, during his experiments, Carver noticed that the Electronic Frequency Control (EFC) voltage required to achieve the nominal 10 MHz output was significantly higher than expected.
Typically, the EFC pin in a VCXO serves as the tuning-voltage input, with a nominal control voltage range of around 0 to 5 V, and 2.5 V often being the mid-point corresponding to the nominal frequency. However, Carver found that he needed to push the EFC up to around 4.34V to achieve the exact 10 MHz output. This higher-than-expected tuning voltage was attributed to the age of the crystal oscillator rather than the nominal specification.
The age of the crystal oscillator can cause changes in its physical properties, shifting the frequency characteristics and requiring different control voltages to maintain the nominal frequency. Other factors that can contribute to deviations from the expected range and center voltage include manufacturing variances, environmental conditions, circuit loading or measurement setup.
To address the lack of information and fill in the missing details, Carver conducted extensive experiments and research. A chart detailing the behavior of the EFC voltage can be found in his linked notes. For those interested in learning more about timing accuracy, precision, and stability, Carver recommends Tom Van Baak's website, LeapSecond.com. For insights into OCXOs, he suggests checking out XOXO For The OCXO and Inside A Vintage Oven Controlled Crystal Oscillator.
For those seeking to measure stable timing sources, Carver suggests searching for "Allan Variance." His own exploration in this area led him to submit a project for the One Hertz Challenge.
[1] Carver, W. (2022). Precise Time Ref via 1 Pulse-Per-Second GPS Signal. Retrieved from [Link to Carver's notes] [2] Carver, W. (2022). EFC Voltage Requirements of a 10 MHz VCXO Oscillator. Retrieved from [Link to Carver's notes]
- The intriguing exploration of timing accuracy by Wil Carver, involving the use of a Piezo 2940210 10 MHz Voltage-Controlled Crystal Oscillator (VCXO), also touched on the role of science and technology, as Carver delved into the theoretical understanding of Electronic Frequency Control (EFC) voltage requirements and the impact of age on a VCXO's performance.
- In his research on the unconventional EFC voltage requirements of a 10 MHz VCXO oscillator, Wil Carver not only focused on the practical aspects of the hardware but also emphasized the importance of technology, particularly the Allan Variance, for measuring stable timing sources, a key aspect of modern science and engineering.
