GPS Accuracy Contest in 2025: Achieving High Precision Time with a Single Pulse-Per-Second Navigation Signal
In the world of precise timekeeping, Wil Carver's latest project, "Precise Time Ref via 1 Pulse-Per-Second GPS Signal," is making waves. The project, submitted for the One Hertz Challenge, aims to create a highly accurate time reference using a GPS Disciplined Oscillator (GPSDO).
At the heart of this project is a Piezo 2940210 10 MHz crystal oscillator, a unique device that serves as both an oven-controlled crystal oscillator (OCXO) and a voltage-controlled crystal oscillator (VCXO). However, an interesting finding emerged during the course of the project.
Typically, the Electronic Frequency Control (EFC) voltage in a VCXO like the Piezo 2940210 is centred around 2.5V. This is the usual midpoint for tuning voltage in standard VCXOs. But Wil Carver discovered that he needed to push the EFC voltage up to approximately 4.34V to achieve the desired 10 MHz output. This discrepancy can be attributed to the age of the crystal oscillator, which likely affected its tuning characteristics and sensitivity[1][2].
The EFC pin in the VCXO serves as the tuning-voltage input. By adjusting this voltage, the frequency of the oscillator can be fine-tuned. In this case, the higher EFC voltage was necessary to compensate for the age-related changes in the oscillator's frequency response.
The GPSDO takes the precision 1 Pulse-Per-Second (PPS) GPS signal and uses it to adjust the 10 MHz crystal oscillator until it repeatedly produces 10,000,000 cycles within one second. This ensures a high degree of precision in the timekeeping.
For those interested in the measurement of stable timing sources, Wil Carver suggests searching for "Allan Variance." This term is often used in the study of clock stability and is a useful resource for understanding the performance of timing devices.
If you're keen on learning more about oscillators, OCXOs, and timing accuracy, precision, and stability, Wil Carver recommends Tom Van Baak's website, LeapSecond.com.
Two resources for learning about OCXOs are XOXO For The OCXO and Inside A Vintage Oven Controlled Crystal Oscillator. These resources provide detailed insights into the workings of OCXOs and are valuable tools for anyone interested in the field.
Detailed notes about Wil Carver's experiments can be found in the linked notes, offering a firsthand account of the challenges and discoveries made during the project.
[1] Wil Carver's detailed notes on the project can be found at the link provided. [2] For more information on the behaviour of EFC in VCXOs, refer to the linked notes.
The hardware component at the heart of Wil Carver's project is a Piezo 2940210 10 MHz crystal oscillator, a device that serves as both an oven-controlled crystal oscillator (OCXO) and a voltage-controlled crystal oscillator (VCXO). The project, being in the field of science and technology, involved the study of EFC voltage in VCXOs like the Piezo 2940210 and its relationship with the frequency of the oscillator, leading to the discovery that a higher EFC voltage was necessary to achieve the desired output.
