Rubidium Reference Oscillator
- Parts per billion accuracy
- Exceptionally accurate and stable
- Expensive if not surplus
- Sporadic availability
- Uncertain reliability if surplus
Until recently, the preferred reference for precise time measurement was the rubidium reference oscillator. These are quartz oscillators that are disciplined by atomic forces to be many times more accurate than a simple quartz oscillator. They’re accurate to about one part per billion. The problem with these circuits is that they’re expensive if you buy them new, the availability of surplus units is sporadic, and the surplus units may or may not work well, or for long.
The following picture shows one type of surplus rubidium reference oscillator used to measure clocks. Rubidium oscillators are exceptionally accurate and stable, and make good references.