Practical_Antenna_Handbook_0071639586

C h a p t e r 1 4 : r e c e i v i n g A n t e n n a s f o r H i g h F r e q u e n c y 357
Figure 14.17 Raising the self-resonant frequency.
Coaxial-Cable Loop Antennas
One of the more effective ways to make a shielded loop is to use coaxial cable. Figure
14.18 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 wound with 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, and the cable 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 at the connector end, not at any other point.