Just finished with my helix antenna, designed for 1240MHz.
Used the helix calculator from http://jcoppens.com/ant/helix/calc.en.php.
Parameters were 1240MHz, 8 turns, 0.23 wavelengths.
My internal helix diameter is roughly 80mm with a coil spacing of 55.5mm. Wire diameter is 3.5mm/10mm².
Reflector size is 250mmx250mm. Center support is made from 6mm Balsa, soaked with epoxy resin.
For matching the IBCrazy wave trap method is used. Trap size is 30mmx15mm. See also http://www.rcgroups.com/forums/showthread.php?t=1377791