Building Helix Antennas by Seattle Wireless
Pay attention on choosing the right PVC pipe.
The Hecker design relies on thin wall material such as under-sink drain pipe. High pressure pipe (thick wall) is a poor choice as the velocity factor of the dielectric has a significant impact on overall tuning.
Helixcalc and others assume open air or close to it. I placed a unit built with high pressure PVC and Hecker’s dimensions on a HP 8720D network analyzer only to find it was optimized for some freq considerably lower than 2425 MHz. See http://www.qsl.net/pa0hoo/helix_wifi/index_eng.htm
Article origiannly available at this address http://www.seattlewireless.net/index.cgi/BuildingHelicalAntennas