The Vortex ‘Super J-Pole’ Antenna consists of a five eighth wave vertical radiator, a half wave tuning section and a half wave top section. At the base, a quarter wave matching stub forms the classic ‘J Shape’. The addition of the extra half wave top section boosts the gain over a standard J-Pole. The Super J-Pole has an added advantage that tuning can be varied over a fairly wide frequency range by moving the feed-point location up or down. This also gives the user finer control over the impedance and match. The antenna is end fed and has an omni-directional radiation pattern and requires no ground plane or radials. The antenna has a nice low angle of radiation, typically 8 degrees when mounted at 4m in height. This angle reduces further the higher the antenna is mounted. A typical installation with the antenna at 8 meters above ground sees the angle reduce to 5 degrees and the gain increases to 7.29dbi when ground reflections are added.
INFO: http://ei4dib.blogspot.ie/2015/09/vortex-super-j-pole-antenna-vhf-70mhz.html
