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.
One of the two 157-degree RG58 sections of the Christman feed. 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 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.
During optimisation measurements were made with a MFJ-259B antenna analyser (tnx Marcus, G0IJZ). Each vertical and two radials were adjusted to resonance (X=0) at 7.050 MHz. The self impedances were measured at 38 Ohms.
The measured SWR of the finished array, with the phasing feedlines, (measured with an FT1000MP), was 1.2:1 at 7.000 MHz dropping to 1:1 at 7.100 MHz.
