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
on a non conductive glass fibre fishing rod (beware of conductive
carbon fibre material!)
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.
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
Performance
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!