I came across a Nortel GPSTM and re-purposed it as a 10MHz reference for my lab. The GPSTM is designed to slot into a backplane, most likely for telecoms applications, so I needed to hack the board to run from a 48v PSU. Once powered up, it was relatively easy to interface as the card appears to contain the well known Trimble Thunderbolt module and is compatible with its software.
The Project
Hardware Setup
The Nortel GPSTM frequency standard provides:
- GPS Disciplined Oscillator - Temperature-controlled crystal oscillator locked to GPS time
- 10MHz Reference Output - Standard lab reference frequency
- 1PPS Output - One pulse per second timing signal
- 48V Power Input - Required custom power supply modification
Technical Details
- Based on Trimble Thunderbolt GPS module
- Provides extremely stable 10MHz reference signal
- Temperature-compensated crystal oscillator (TCXO)
- GPS-locked for long-term accuracy
- Compatible with standard lab equipment reference inputs
Why Frequency References Matter
Frequency references are a valuable addition to any electronics lab. On the back of most oscilloscopes, spectrum analyzers, and function generators you’ll find a 10MHz reference input allowing the user to supply a reference more accurate than that generated internally.
Benefits of External References
- Higher Accuracy - External references are often more accurate than internal oscillators
- Equipment Synchronization - Keep all equipment in sync with a common reference
- Precise Measurements - Critical for accurate timing and frequency measurements
- Long-term Stability - GPS-disciplined references maintain accuracy over time
The Hack
Power Supply Modification
The original GPSTM was designed for backplane installation with 48V power. I needed to:
- Identify Power Pins - Trace the power connections on the backplane connector
- Build 48V Supply - Create a suitable power supply for the module
- Interface Connections - Connect the reference outputs to standard connectors
- Software Configuration - Use Trimble Thunderbolt software for configuration
Technical Challenges
- Power Requirements - 48V supply with proper current capability
- Signal Levels - Ensuring proper voltage levels for lab equipment
- GPS Antenna - Providing clear sky view for GPS lock
- Software Interface - Configuring the module for optimal performance
Lab Integration
Equipment Synchronization
Once operational, the frequency reference can synchronize:
- Oscilloscopes - For precise timing measurements
- Spectrum Analyzers - For accurate frequency analysis
- Function Generators - For stable output frequencies
- Network Analyzers - For RF measurements
Measurement Benefits
- Reduced Jitter - Cleaner, more stable signals
- Better Accuracy - Improved measurement precision
- Time Correlation - All measurements referenced to common time base
- Professional Results - Lab-grade frequency stability
Alternative Approaches
Commercial Solutions
- Rubidium Standards - Higher accuracy but more expensive
- OCXO Modules - Good stability without GPS
- GPS Disciplined Oscillators - Various commercial options available
DIY Alternatives
- GPS Modules - u-blox modules with 10MHz output
- Temperature-Controlled Oscillators - TCXO modules with GPS discipline
- Atomic Clocks - Cesium or hydrogen maser standards (for serious time-nuts)
Lessons Learned
Technical Insights
- GPS Discipline - Provides excellent long-term stability
- Temperature Control - Critical for frequency stability
- Power Quality - Clean power supply essential for performance
- Antenna Placement - Clear sky view required for GPS lock
Project Value
This project demonstrates how surplus telecom equipment can be repurposed for lab use. The Nortel GPSTM provides professional-grade frequency reference capabilities at a fraction of the cost of new equipment.
Impact and Recognition
This project was featured on Hackaday, highlighting the value of repurposing surplus equipment for electronics labs. The hack shows how telecom-grade frequency standards can provide excellent reference signals for precision measurements.
The project also sparked discussion in the time-nuts community about frequency reference options and the benefits of GPS-disciplined oscillators for lab applications.
Getting Started
For Your Own Lab
- Find Surplus Equipment - Look for telecom frequency standards
- Understand Power Requirements - Check voltage and current needs
- Plan Integration - Consider how to connect to your equipment
- GPS Antenna - Ensure clear sky view for GPS lock
- Software Tools - Get appropriate configuration software
Resources
- Time-Nuts Mailing List - Community of frequency reference enthusiasts
- Surplus Equipment - Check telecom equipment auctions
- Documentation - Look for technical manuals and schematics
- Software - Trimble and other GPS module configuration tools
This project exemplifies the hacker spirit of taking surplus equipment and repurposing it for new applications, turning telecom infrastructure into precision lab equipment.