"Homebrew" 435MHz 12-turn Helix Antenna
Par/By: Bertrand Zauhar, VE2ZAZ.
This 50-ohm impedance antenna, when fed with 25-100W of SSB RF at 435MHz, makes reaching Amateur satellites such as AO-40 and AO-10 a snap! 

The gain of this antenna is estimated at 13dBi.

This section is presented to give you ideas on how to achieve a sound mechanical construction, instead of giving you an exact recipe to follow.

I  used the following dimensions for construction:

Wavelength :
l = 68.9 cm
Boom length :
Lboom = 210 cm
Turn spacing :
S = 0.22 x l = 15.2 cm
One turn diameter :
Fturn = 20.8 cm
Reflector diameter :
Frefl = ~1.0l = 70 cm
Standoff spacing :
Lsupp = 1.5 x S = 22.8 cm
Coupling strip 
width :
Wcoupl = 2.5 cm
Wire one-turn radius :
R = 0.15  x l = 10.4 cm
One turn Circumference :
65.3 cm
One turn wire length :
67.1 cm

The following materials were used to build the 12-turn helix:


Assembly Notes: 

The final SWR adjustment is performed  by sliding the reflector assembly. The N-connector center pin, lenghtened by a piece of AWG 12 gauge wire, is fed through a hole made in the helix tubing, but is not soldered to it. Center pin is only soldered to helix tubing when completed.

For more information on the helix antenna, please refer to the following reference books available at http://www.arrl.org

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