C-POLE PORTABLE ANTENNA FOR 20M
A vertical that's small, light and portable, needs no counterpoise and performs as well as a home antenna
C-Pole Antenna for 20m
Dimensions of C-Pole Antenna for 20m
[Design frequency 14.240 MHz]
Overall wire length roughly 1/2 wavelength, feedpoint 25% from end,
electrically an off center fed dipole.
The two stubs -- 10cm and 5cm -- at the insulator on the left of the drawing
are to be trimmed for fine tuning, the lower for best SWR, the upper for resonance.
Detail of insulator and the two stubs
The dimensions for other frequencies can be computed by multiplying the above values
with the design frequency, divided by the target frequency:
Formula for 17m [18.120 MHz]
Detail of Balun and Feedpoint (experimental hookup)
1:1 Current-Balun, 2 x 7 turns RG-174 Teflon on Amidon FT-240/61
(loss about 0.3 dB on all bands [Brian, KF2YN])
Current-Balun in waterproof box
Excellent SWR, easily adjustable to desired frequency!
EZNEC simulation of take-off angle versus hight of bottom wire/ground.
The resonant frequency increases with height/ground,
add some extra wire length if you rise the C-Pole!
Alternative Coax-Balun, 60 turns RG-58 on 48 mm plastc tube
(loss about 0.6 dB on 20 m, about 0.8 dB on 10 m [Brian, KF2YN])
SWR between 3 MHz and 30 MHz, Toroid-Balun vs. Coax-Balun,
both terminated with 50 Ohm Dummy-Load
My results with C-Pole are surprising:
OH0/ES1AX, D4B, 9Y4ZC, SV9/F6JXR, SV8/DF1UX/mm, 7X3VRK, 4X0T, 9H3YM, EI6JK from HB9 within the first few hours with FT-817 and 4W-50W! Recently I picked HS0/IK4MRH out of a huge pile up!
See original article in QST 2004/4, P.37:
The "C Pole" - A Ground Independent Vertical Antenna
Brian V. Cake, KF2YN
See Sangamon Valley Radio Club for: Java-based C-Pole Calculator
See Chuck's C-Pole: W5USJ
See EZNEC-File: c-pole-20m.ez