Several documents describe aspects of the continuing development of a multichannel, dual-mixer system for simultaneous characterization of the instabilities of multiple precise, low noise oscillators. One of the documents presents the basic principles and design concept that were summarized in "Oscillator-Stability Analyzer Based on a Time-Tag Counter" (NPO-20749), NASA Tech Briefs, Vol. 25, No. 5 (May 2001), page 48. To recapitulate: One of the oscillators would be deemed to be a reference oscillator, its frequency would be offset by an amount (100 Hz) much greater than the desired data rate, and each of the other oscillators would be compared with the frequency-offset signal by operation of a combination of hardware and software. A high-rate time-tag counter would collect zero crossing times of the ≈100-Hz beat notes. The system would effect a combination of interpolation and averaging to process the time tags into low-rate phase residuals at the desired grid times. Circuitry that has been developed since the cited prior article includes an eight channel timer board to replace an obsolete commercial time-tag counter, plus a custom offset generator, cleanup loop, distribution amplifier, zero-crossing detector, and frequency divider.

This work was done by Albert Kirk, Steven Cole, Gary Stevens, Blake Tucker, and Charles Greenhall of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the Electronics/Computers category.