Stability of high quality quartz crystal oscillators: an update

Two specially modified low-level, high-quality 5 MHz oscillators were tested for spectral purity and stability at the National Institute of Standards and Technology. Using a third, high-quality, prior-technology oscillator for triangulation the individual phase-noise power spectral density of one of the oscillators was determined to be S_φ(f)=-133 dB±2 dB below 1 rad ²/Hz at a Fourier frequency of 1 Hz, while for the second oscillator it was -125 dB±2 dB at 1 Hz. Such oscillators can exhibit parts-in-10¹⁴ flicker floor stability in high-precision quartz frequency-source applications. Extensive details of measurement methodology are given