During the PACC contest in 2009 we missed a good performing antenna for 40m. So during the preparation for this contest in 2010 I built a dedicated vertical for 40m.
The vertical itself is a simple wire, like the ones they use to power wall outlets and light switches in your home. It is a copper wire, 2,5mm2, isolated. It is 9,80m tall, and erected by using a 12m PVC pole.
On the ground a net of wires is made, in a star shape. The center of this net is a ring made of copper pipe. Holes are drilled into that pipe, to hold bolts and nuts to connect the wires. I added some AMP-connectors to enable easy connecting/disconnecting the ground wires. The ground wires itself have different lengths. We started with 4 wires of 15m, 4 of 10m, and 8 of 5m. The wires are laying on the ground. Put the 15m wires in each wind direction, the 10m wires inbetween them, and then the 5m wires inbetween the 10 and 15m wires.
The antenna impedance is too low to connect to the coax. So I builded a simple matching box holding a T-filter. The box itself was originally made to hold food to put in your freezer. But these boxes are also very handy and waterproof to hold a matching circuit.
See the pictures down here to get an idea of the construction…