Radial Line Slot Antenna
The slot antenna, consisting of a narrow slit in a ground plane, is a very versatile antenna. With modification, it is amenable to waveguide, coplanar waveguide (CPW), coaxial, slot line, or microstrip feeding schemes and has been used in all aspects of wireless and radar applications. Finally, starting from the antenna end of the radial wires and about every three-to-four feet, hold the wire down with a radial wire staple while pulling the radial out from the antenna to keep it taut. Push it in as far as possible to get the wire as close to the grass roots as possible. I typically use a hammer or rubber mallet to drive it home. A radial system has two main purposes, replace the missing half of the antenna (a vertical is simply a dipole with earth sub- stituting for the missing half when set vertical, unfortunately earth is a very poor RF conductor) and forming an electrostatic shield to prevent much of the RF on the vertical element from capacitively cou- pling to the lossy soil.
The best time to put down radial wires for your amateur radio setup is early spring but it can be done other times as well. I have even done it in the fall and had good success.
Antenna Radial Length
The idea behind installing radial wires without digging is to let your grassy lawn grow over the radials and protect them from the mower. You don't have to trench or bury them!
First, mow the grass pretty short in the areas where you will be laying the radial wires down. Notice, I didn't say 'scalp' it—just lower the mower until the grass is about one-inch long after cutting. (Remember to readjust the height of the mower back to normal before you put it away).
Next, connect the radial wires to the radial plate with wire terminal ends and stretch them out while arraying them evenly around the antenna (that’s what 'radial' means).
Radial Wires Attached to the Radial Plate
Note: Red wires were used so they can be seen in the pictures. DX Engineering Radial Wire has a Black relaxed PVC insulation.
Some AM broadcast engineers might tell you that the radials should be as long as you can make them - up to about 1/2 wavelength. However, if you can only do 1/4-wave or 1/8-wave in certain directions then do it and don’t worry about it. They won't be resonant since they are lying on (or in) the ground. You will be surprised how much better your vertical will work. After you install a few radials and see how much better you antenna performs you will have an urge to put in more of them. Remember, laying them on the ground (or burying them) detunes them, so electrical length is relatively unimportant. Don’t resist - more is better.
Finally, starting from the antenna end of the radial wires and about every three-to-four feet, hold the wire down with a radial wire staple while pulling the radial out from the antenna to keep it taut. Push it in as far as possible to get the wire as close to the grass roots as possible. I typically use a hammer or rubber mallet to drive it home. If a radial wire is sticking up any place due to uneven ground or the wire is loose just put another anchor pin there. The idea is to get all parts of the wire down as close as possible to the ground so that the grass can grow over it.
Radial Wires held in place with Staples
Here are some pictures of what it should look like.
Two examples of radial wires installed
Slot Antenna Design
When you finish the last radial wire, your job is done. Mother Nature will do the rest. If you have done this in the early spring, the grass will grow up and surround the wires. The root system will also pull the radial wires down firmly along their full length. If you do it in the fall after the grass has stopped growing, it will happen the next spring. This will be done so completely that in a few weeks you will have to actively look for the radial wires to see them. Your mower will miss them completely, too. But you and your contacts will hear them right away!
73,
Slot Antenna Pdf
Paul, NO8D