No. 18 drill Sufficient size to accommodate transmission line cable C/L Fuselage skin Antenna Existing stringers Reinforcing doubler Alclad 2024-T3 Approximately one inch spacing of  $^{1}$/8 " minimum diameter rivet  A A View - A A 1½$^{"}$ edge distance minimum Figure 11-161.  A typical antenna mounting template.  Figure 11-162.  A typical antenna installation on a skin panel  including a doubler.  mast and the fuselage with a suitable sealer, such as  zinc chromate paste or equivalent. The mounting bases of antennas vary in shape and sizes;  however, the aforementioned installation procedure is typical  of mast-type antenna installations.  A transmitting or receiving antenna is connected directly to its  associated transmitter or receiver by a transmission line. This  is a shielded wire also known as coax. Transmission lines may  vary from only a few feet to many feet in length. They must  transfer energy with minimal loss. Transponders, DME and  other pulse type transceivers require transmission lines that  are precise in length. The critical length of transmission lines  provides minimal attenuation of the transmitted or received  signal. Refer to the equipment manufacturer’s installation  manual for the type and allowable length of transmission  lines. To provide the proper impedance matching for the most  efficient power transfer, a balun may be used in some antenna  installations. It is formed in the transmission line connection  to the antenna. A balun in a dipole antenna installation is  illustrated in  Figure 11-163 .  Coax connectors are usually used with coax cable to ensure  a secure connection. Many transmission lines are part of  the equipment installation kit with connectors previously  installed. The aircraft technician is also able to install these  connectors on coax.  Figure 11-164  illustrates the basic steps  used when installing a coax cable connector. When installing coaxial cable, secure the cables firmly  along their entire length at intervals of approximately 2  feet. To assure optimum operation, coaxial cables should  not be routed or tied to other wire bundles. When bending  coaxial cable, be sure that the bend is at least 10 times the  size of the cable diameter. In all cases, follow the equipment  manufacturer’s instructions.  Detailed instructions, procedures, and specifications for  the servicing of avionics equipment are contained in the  manufacturer’s operating manuals. Additional instructions  for removal and installation of the units are contained in the  maintenance manual for the aircraft in which the equipment  Maintenance Procedure Transmission Lines 11-76