Quadrifilar Helix Antenna
The helical elements are LMR-400 coaxial 
cable. Structural parts are made of 42 mm 
o.d. PVC plastic pipe and 16 mm o.d. CPVC 
pipe. A collar (pipe cap with end removed) 
adds thickness to support the four upper 
half-tubes.

The www.jcoppens.com javascript calculator 
was used to compute exact dimensions. 
Specifications are 137.62 mHz, 10.1 mm 
conductor diameter, width to height ratio 
0.44:1, and bending radius =15 mm.

This version has an internal ferrite sleeve 
balun on the central coaxial feedline. The 
two piece vertical tube is joined with a 
coupling so the antenna can be packed
for travel or storage. No glue or fasteners are 
used except for the feed line connections.

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