Improved Offset Generator Developed for Allan Deviation Measurement of Ultra Stable Frequency Standards

摘要

Measuring the performance of ultra stable frequency standards such as the Superconducting Cavity Maser Oscillator (SCMO) will necessitate improvement of some test instrumentation. The frequency stability test equipment used at JPL includes a 1 Hz Offset Generator to generate a beat frequency between a pair of 100 MHz signals that are being compared. The noise floor of the measurement system using the current Offset Generator (1.7 X 10(exp -14) at 1 second tau and 6.2 X 10(exp -17) at 1000 seconds), is adequate to characterize stability of hydrogen masers, but will not be for the SCMO. A new Offset Generator with improved stability has been designed and tested at JPL. With this Offset Generator, and a new Zero Crossing Detector recently developed at JPL, the measurement floor has been reduced by a factor of 5.5 at 1 second tau, 3.0 at 1000 seconds, and 9.4 at 10000 seconds, compared against the previous design. In addition to the new circuit designs of the Offset Generator and Zero Crossing Detector, tighter control of the measurement equipment environment has been required to achieve this improvement. The design of the new Offset Generator will be described, along with details of the environment control methods used.