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st: Checking for Periodicity in Extremely Dense data


From   "Dan Weitzenfeld" <dan.weitzenfeld@emsense.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Checking for Periodicity in Extremely Dense data
Date   Tue, 17 Jun 2008 15:39:33 -0700

Hi Folks,
I'm working with 60 hz data, and I'm checking for periodicity at the
.2-.4 Hz range.   When I use the command -pergram-, the frequencies I
would like to look at are scrunched up in the far left side of the
graph, (I think) because the frequency of my data so dominates the
frequency of interest.
My knowledge of signal processing is very limited.  Is there an easy
way to get confirm my hypothesis of periodicity at .2-.4 Hz given my
situation?
The workaround I am using is cutting down the density of my data to 30
Hz, then 15 Hz, then 7.5 Hz by simply dropping every other observation
each time, and redefining my -tsset- variable accordingly.  I fear I
may be opening myself up to aliasing effects by doing this.
Any feedback would be much appreciated, even if it is just a pointer
to a good web resource.
Best,
Dan
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