How to Build a Flat AM Loop Antenna
By Eli Laurens
Amplitude modulation (AM) radio receivers can use a variety of antenna designs, and one that offers superior reception is the loop antenna. This very simple design can outperform other styles, and is an inexpensive way to extend the range of most AM radios. The radio should have two antenna lead screws -- positive and negative -- but the casing can be opened for access to the circuit board if exterior leads are not present. The average radio technician can make a flat loop antenna in about 30 minutes.
Cut the cardboard into two squares, each 3 inches by 3 inches, using the scissors.
Cut a notch into each one from the center of an outside edge to the center of the square.
Fit the two cardboard squares into each other by sliding their notches together. They should seat when their centers touch, creating a cross. Use a small section of tape to hold the cardboard in place.
Wrap the cross along the outside edge with about four feet of insulated wire. Keep the wire uniform, and spaced evenly. The wire can touch itself as it loops around the cardboard, but leaving an even gap creates a better signal to noise ratio. Secure the wire to the cardboard with long strips of tape. Leave a couple of feet of wire on each end of the antenna for connecting it to the radio.
Strip the insulation from the ends of the wire leads, leaving about an inch of exposed copper.
Loosen the external antenna terminal screws counterclockwise, but do not remove them.
Bend the exposed wire into a loop and fasten each one around an antenna terminal screw. The wire loop should be around the screw post, under the head.
Tighten the antenna terminal screws clockwise until they are tight. The wire loop will be pinched in between the screw and the backing plate.
Mount the cardboard loop antenna as high as possible, using the tape to fasten it to a post or door frame. The longer the lead wires, the higher the antenna can be mounted. Increasing height will increase reception.
- Making two cardboard crosses and looping the wire around both in a "figure 8" pattern will improve range.
- Use caution when working on radio equipment, and be sure to ground the unit properly.
Eli Laurens is a ninth-grade physics teacher as well as a computer programmer and writer. He studied electrical engineering and architecture at Southern Polytechnic University in Marietta, Ga., and now lives in Colorado.