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Making a periodogram

The Operations menu offers you several options, lets first look at the Operations=>Find Periodicities item. Selecting this will generate a Periodogram Analysis popup window.

periodogram_popup.gif

This popup will try to suggest reasonable values for the minimum and maximum frequency, and frequency interval, based on the Nyquist frequency of the data itself. Alot of the time the suggested values are reasonable, but you should use your common sense, the larger the number of ``frequency steps'' the longer the periodogram will take to generate.

Currently there are two type of periodogram analysis available, Fourier Power Spectrum and Chiq-squared Periodogram. For now lets go with the default options. Hit the Ok button.

This will generate a fourier transform of your data, labelled periodogram 1 and an associated meta-data popup.

fft.gif

Meta-data popups are automatically generated every time you carry out an operation on your data to keep you informed. You can turn off the appearance of these poups by using the toggle swicthes in the Options=>Automatic Display menu.



next up previous 107
Next: Folding time series data
Up: Getting started
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FROG - A Time Series Analysis Package
Starlink User Note 254
Alasdair Allan
21 Apr 2004
E-mail:frog@starlink.ac.uk

Copyright © 2001-2004 Council for the Central Laboratory of the Research Councils