Here is just another way to make a helical antenna. Cheap and easy. Aluminum sheet reflector, cardboard tube and self-adhesive copper tape. Designed and tuned for 1240MHz this helical has 8 turns on a 85mm diameter tube.
Added some eye-candy after flight testing. Performance is excellent. No difference to the wire wound helical I built earlier..
This is an example how one can hit the target on spot with a clean build even on 5.8GHz.
- Design frequency 5800MHz
- 8 turns
- Wavelength 0.23
- Internal diameter 17-17.5mm
- Wire diameter 1mm
- Coil spacing 11.8mm
- Reflector 40mmx40mm
- Wave Trap size 6.5mmx3.2mm
- Wave Trap spacing from feed point 2mm
- Feed point height 2.5mm (wire center), maintained over 1/4 turn
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