This antenna was developed from an idea of combining the simplicity of the 1/8th wavelength spaced Christman fed array with the simplicity of directional elevated radials. The antenna has 3dB gain over a single vertical. Importantly, for this DXpedition, it's light to transport, and easy to put up.
Close up of the feedpoint of one of the verticals. The grey pipe is a 55mm plastic drainpipe used to protect the fibre glass mast in transit. The feedpoint is a few inches above ground level and the radials go up from the coax socket to cane supports and then horizontally off at 1m above ground level.
The T-piece at the end of the 39-degree feeder section. The DK9SQ 10m poles are dropped into transport-protection tubes. These tubes are strapped to fence posts hammered into the ground.
The feeders are coiled up to make choke baluns at the base of each vertical.
This antenna design is described on page 11-35 of "Low band DXing" (3rd Edition, 1999) by John Devoldere, ON4UN.
The dimensions for the 40m North facing implementation, with elevated radials.
The EZNEC wire model for the simulation. The quarter-wave verticals are supported by DK9SQ fibre-glass poles. Each vertical has 2 radials elevated 1m above ground. Each radial is angled at 30 degrees from the main direction of fire. Wire lengths are, both verticals = 11.07m, all four radials = 9.68m.
The 3D radiation pattern. The simulation models real copper and ground losses. Ground parameters 5 mS/m with a dielectric constant of 13, typical of real soil.
Elevation plot showing best gain at 25 degrees elevation.
Azimuth plot showing 126 degree beamwidth and good front-to-back ratio.