
Allan Variance is the fractional frequency deviation versus the
averaging time when N = 2 and T = r. This section describes the
process used by the HP 3048A to calculate sigma of r and the Allan
Variance.
Softkey Descriptions
Eval Sigma: Initiates the calculation of Sigma when N, T, r, and f
h
are specified.
Eval
Allan:
Calculates Sigma when r and f
h
are specified.
*Omit Spurs: Calculates Sigma excluding the spur contributions for
the specified entries.
Plot: Plots all calculated Sigma on a Sigma versus Tau graph.
Description
Sigma vs. Tau
The following equations define fractional frequency deviation versus
averaging time.
\ h=\ fc=l /
where : /^ = noise bandwidth
and : ( ) = infinite time average
and : Y^ = average frequency over Kth time interval of length T
{as would be determined by a high resolution counter)
4-10 Sigma vs. Tau rev.05SEP89
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