I think a program called PERSCAN from the U.K. does this. I seem to
remember that it picks out periodicity of hydrophobic residues. It's
been a while since I looked at it, so I may have it all wrong. I
think the author is Dan Donohue.
Matt Harrington matt at sbl.salk.edu
The Salk Institute http://sbl.salk.edu/~matt
San Diego, CA