Decade Resistance Box
Homebrew calibration guide for Decade Resistance Box using fundamental physical constants and freely available reference signals - no expensive calibrated equipment needed!
Equipment Specifications
Primary Reference: Precision resistor standards
Expected Accuracy: ±0.1% resistance
Difficulty: Beginner to Intermediate
Build Time: 3-5 hours
ESP32/CYD: No
What We'll Use
- WWV/WWVH - NIST time signal stations (better than 1×10⁻¹² accuracy)
- GPS 1PPS - GPS satellite timing (±40 nanosecond accuracy)
- AC Mains - Power line frequency (60 Hz ±0.02 Hz)
- Precision Resistors - 0.1% tolerance, NIST-traceable
- Physics Calculations - Known resonant frequencies, Ohm's law
What You'll Build
A complete calibration fixture including:
- Precision voltage references (multiple tap points)
- Frequency reference receiver (WWV or GPS)
- Measurement circuits designed for bootstrap calibration
⚡ Safety First!
Some calibration methods involve AC mains voltage. Always use proper isolation, work in well-ventilated areas, and never work on live circuits unless absolutely necessary. When in doubt, consult a qualified professional.
Cost Breakdown
Total parts cost: $40-75
- Precision voltage references: $5-10
- Precision resistors (set of 5): $5
- GPS module with 1PPS: $10-15
- Enclosure and connectors: $10-20
- Miscellaneous (perfboard, wire, etc.): $5
Compare to: Professional calibration service costs $100-500+ per instrument!
Results You Can Expect
Using these homebrew calibration methods, you can achieve:
- ±0.1% resistance - Better than many factory calibrations!
- Long-term stability when using quality components
- Traceable to NIST standards (through WWV and GPS)
- Repeatable measurements for ongoing equipment verification
Ready to Get Started?
Download the complete documentation and start building your calibration fixture today!
View Full Calibration Guide →What's Included in the Guide
- Complete theory of operation
- Detailed reference standard descriptions (WWV, GPS, precision components)
- Full schematics and parts lists with sources
- Step-by-step construction procedures
- Assembly instructions with photos/diagrams
- Complete calibration procedures with datasheets
- Troubleshooting guide
- Example calibration runs with actual measurements
Bootstrap Philosophy
"How do you calibrate test equipment when you have no calibrated equipment?"
This is the classic metrology "chicken and egg" problem. The answer is to use fundamental physical constants and references derived from national standards laboratories.
WWV radio stations are synchronized to NIST's atomic clocks with better than 1 part per trillion accuracy. GPS satellites carry atomic clocks synchronized to USNO master clocks. These signals are freely available and provide references accurate enough to calibrate virtually any consumer or amateur radio test equipment.
Combined with precision components (0.1% resistors, calculated inductors, precision capacitors), we can build calibration fixtures that are often MORE accurate than factory calibrations!