Plane of loop perpendicular to direction of wave travel Plane of loop parallel to direction of wave travel Maximum reception loop orientation Minimum reception loop orientation A. B. Protective plastic covering Shielding–Outer conductor Central conductor Dielectric–Insulator 11-42 Figure 11-94.  Coaxial cable is used as the transmission line between an antenna and its transmitters and/or receiver.  Figure 11-93.  A loop antenna is highly direction-sensitive. A signal origin perpendicular or broadside to the loop creates a weak signal  (A). A signal origin parallel or in the plain of the loop creates a strong signal (B).  Transmission Lines Radio Navigation Transmitters and receivers must be connected to their  antenna(s) via conductive wire. These transmission lines  are coaxial cable, also known as coax. Coax consists of a  center wire conductor surrounded by a semirigid insulator.  Surrounding the wire and insulator material is a conductive,  braided cover that runs the length of the cable. Finally, a  waterproof covering is set around the braided shield to protect  the entire assembly from the elements. The braided cover  in the coax shields the inner conductor from any external  fields. It also prevents the fields generated by the internal  conductor from radiating. For optimum performance, the  impedance of the transmission line should be equal to the  impedance of the antenna. In aviation antenna applications,  this is often approximately 50 ohms.  [Figure 11-94]  Special  connectors are used for coaxial cable. A variety can be  In the early years of aviation, a compass, a map, and dead  reckoning were the only navigational tools. These were  marginally reassuring if weather prevented the pilot from  seeing the terrain below. Voice radio transmission from  someone on the ground to the pilot indicating that the aircraft  could be heard overhead was a preview of what electronic  navigational aids could provide. For aviation to reach fruition  as a safe, reliable, consistent means of transportation, some  sort of navigation system needed to be developed. seen in Advisory Circular (AC) 43.13-1b, Chapter 11,  Section 17, Figure 11-37. The technician should follow all  manufacturer’s instructions when installing transmission  lines and antenna. Correct installation is critical to radio and  antenna performance.