Clare's (VE3NPC) helix article in the AMSAT Journal (May-June 2006) is to me one of the best researched and best written articles on helix antennas. Of the many questions researched, It deals with the turns vs. gain and PVC usage questions in which everyone seemed to have a varying opinion.
There are advantages and disadvantages to each type antenna
Here are some helix info websites.
1.http://www.qsl.net/ve3cvg/antennas/ Good antenna website plus 2400 MHz helix.
2.http://www3.sympatico.ca/b.zauhar/ A lot of info on this page with 2400 and 435 MHz helix projects.
3.http://www.g6lvb.com/index.htm Great site! Check out quadruple helix for AO40.
4.http://members.aol.com/k5oe/ Jerry's site has a lot of useful helix data. Check out the helix projects by clicking the home brew page at left bottom.
5.http://www.electric-web.org/2m_helix_antenna.htm VK5ZAI's 2 meter helix
6.http://webpages.charter.net/n4wyk/ Click satellite website then click 2401 MHz helix at left.
7. The 2006 ARRL Handbook has a excellent "L" band helix project.
73, Mike K9QHO AMSAT 33589