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 holl_ands | Home > Circular Polarized incl. Rabbit-Ears > Helical Circular Polarized  
Helical Circular Polarized
Helical (Axial-Mode) Circularly Polarized (CP) Antennas analyzed using 4nec2 for Hi-VHF Band.

FYI: Some (mostly narrowband) Helical Antenna Design links:
https://www.cv.nrao.edu/~demerson/helixgain/helix.htm  [Max Gain Parameter Charts]
http://www.daycounter.com/Calculators/Helical-Antenna-Design-Calculator.phtml
http://www.vk2zay.net/calculators/helical.php
http://scholar.lib.vt.edu/theses/available/etd-120899-112725/unrestricted/etdig.pdf
http://www.antenna-theory.com/antennas/travelling/helix.php
Date(s): 9 Feb 2001. 1 - 2 of 2 Total. Shared
Hi-VHF Helical - Offset Feed
1. Hi-VHF Helical - Offset Feed  (9 Feb 2001)
Hi-VHF Helical (Axial-Mode) Circularly Polarized Antennas with Off-Set Feed is analyzed using 4nec2.

1) Hi-VHF: Offset Feed, 185 MHz Design Frequency, 5.5 Turns, C/WL=1.133 (presumably close to optimum),
Alpha=arctan(S/C)=14.5-deg (presumably close to optimum), where C=Helix Circumference, WL=Wavelength,
Alpha=Helix Spiral Angle and S=Size of One Turn along the X-axis.
Calculated parameters: R=29.24-cm (11.5")=Helix Radius, S=47.52-cm (18.7") and L=2.6134-m (102.9")=Helix Length.

Characteristic Impedance is optimum (under 1.4) for 200-ohms, but is still quite good at 300-ohms, as plotted below.

EDIT (19 Jan 2011): Added Circular Polarization Patterns as an Animated-GIF.....Looks Good....
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Hi-VHF Helical - Center Feed
2. Hi-VHF Helical - Center Feed  (9 Feb 2001)
Hi-VHF Helical (Axial-Mode) Antennas with Center Feed is analyzed using 4nec2.

1) Hi-VHF: Center Feed, 185 MHz Design Frequency, 5.5 Turns, C/WL=1.133 (presumably close to optimum),
Alpha=arctan(S/C)=14.5-deg (presumably close to optimum), where C=Helix Circumference, WL=Wavelength,
Alpha=Helix Spiral Angle and S=Size of One Turn along the X-axis.
Calculated parameters: R=29.24-cm (11.5")=Helix Radius, S=47.52-cm (18.7") and L=2.6134-m (102.9")=Helix Length.

Characteristic Impedance is optimum (under 1.24) for 120-ohms, but is still quite good at 75-ohms, as plotted below.

EDIT (16 Jan 2011): Added Circular Polarization Patterns as an Animated-GIF.
Only Good for the lowest frequencies.  NEEDS FURTHER INVESTIGATION AND/OR REDESIGN!!!!
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