Time Domain Frequency Stability Calculated from the Frequency Domain Description:Use of the SIGINT Software Package to Calculate Time Domain Frequency Stability from the Frequency Domain

摘要

The authors describe the use of SIGINT, an interactive software package developedby the National Institute of Standards and Technology, which facilitates the calculation of time domain frequency stability from frequency domain data as a function of measuring time in terms of either the Allan variance (sigma squared(sub y))(tau); the modified Allan variance, mod(sigma squared(sub y))(tau); or (sigma squared(sub y))(tau)=(tau/(square root of 3))mod(sigma squared(sub y))(tau). Except for the graphic output, the code is written in standard FORTRAN 77 and runs on AT compatible computers that have a math co-processor. It also runs on many other systems; however, calls to an available graphics library will need to be substituted for those that are included in this version. The program uses either a user defined function for the input noise or default functions that describe the noise types commonly found in oscillators, amplifiers, frequency multipliers, frequency dividers, and general signal processing equipment including up to four coherent bright lines in the noise spectra. These default functions make it simple to analyze the time domain frequency stability as a function of measuring bandwidth using realistic first-, second-, or third-order low-pass filters or the simplified infinitely sharp cutoff parameter. The default functions are also set up to examine the effect of various servo parameters on the performance of a frequency source locked to a frequency reference.