Coaxial-cable loop antennas

One of the more effective ways to make a shielded loop is to use coaxial cable. Figure 15-14 shows the circuit of such a loop. Although only a single-turn loop is shown, there can be any number of turns. One reader made a 100-kHz LORAN (a navigation system) loop using eight turns of RG-59/U coaxial cable on an 8-ft diameter. Note the special way that the coaxial cable is connected. This method is called the Faraday connection after the fact that the shield of the coax forms a Faraday shield. At the output end, the center conductor of the coaxial cable is connected to the center conductor of the coaxial connector. The coax shield is connected to the connector ground/shield terminal. At the other end of the loop, the shield is left floating, but the center conductor is connected to the shield. Note very carefully that the center conductor at the far end is connected to the shield at the connector, not at just any convenient point.