A dipole is a balanced antenna and should not be fed directly with coaxial cable. Doing so would cause the outer conductor of the coaxial line to act as part f the antenna, and a large amount of signal would be radiated or received by he outer conductor. For casual reception his may not matter much, but the directional radiation pattern of the antenna is destroyed and reception / transmission results are no longer predictable. In order to derive a balanced feed for the dipole some sort of a transformer is necessary. For the corner reflector described here a slot-fed balun is used (see Fig.
1). This is accomplished by splitting the outer conductor (made from a brass tube) lengthwise for a quarter wavelength and connecting the inner conductor (a much smaller diameter tube or rod) to the end of one segment, and to one dipole element. The other segment is connected to the opposite half of the dipole. This type of balun gives a 4: 1 impedance transformation and can feed a simple dipole. The slot-fed balun is used as the dipole operation. The dipole use is a brass rod of 1/16 inches outer diameter.
The dipole length is 2 x 5 inches long. First half of the dipole is soldered to the inner rod and outer tube of the feedline. The second half of the dipole is soldered to the outer tube only. The feedline consists of a tube of 5/8 inches outer diameter x 19/32 inches inner diameter brass tubing, 9. 5 inches long and an 1/4 inches outer diameter brass rod, 9. 3 inches long.
1/4 inches O. D. rod is the inner rod and the 5/8 inches brass tube is the outer tube. The inner rod is placed inside the outer tube to create a coaxial feedline with air dielectric.
The outer tube was cut to make a slot of 1/4 wavelength of the operating frequency which is approximately 4 inches long Stiff aluminum material was used to make the reflector. A 0. 019-inch thick perforated aluminum sheet was used. It is available in hardware stores for making grilles and covers for radiators.
The holes reduce the overall weight and wind resistance. Solid sheet aluminum was used since all you need is a conducting surface. Referring to the figure. , you see that the reflector is made by bending a I x 2-foot sheet of perforated aluminum sheet. Instead of one 90-degree bend, two 45- degree bends were used leaving a 1-5/8-inch valley that provides a surface for a wood mechanical support. A piece of 1-7/8 X 3/4 X l 1-inch wood is used to support the reflector and to mount the dipole in the center of the reflector..