TV and FM antenna installation practices will be preferred to throughout this discussion. Installing TV and FM antennas portrays fairly standard practices that should be followed when doing any kind of communications antennas installation.
Never neglect safety. Standard operation procedure should always make safety first on the list of things to do. Locate power lines, telephone lines, and obstacles that could interface with the installation or present a hazard to the installers. A tower structure would require a concrete base as the supporting structure. Guy wires need room for proper mounting. Anchor ladder securely. Use safety belts or harnesses whenever climbing towers or other structure. Be aware of building codes and follow installation procedures supplied by the equipment manufacturer. Heed the equipment manufacturer’s warning.
Grounding and Lighting Protection
Antennas on high exposed metal masts are subject to being struck by lightning. Ground the mast by connecting a wire to it and to ground rod. When the mast is struck by lightning the surge of electricity will be shorted to ground. Some antenna installations require several such ground connections. A typical ground wire size for a TV or FM antenna is 10 AWG. Local ordinances should specify wire size and type for grounding application. A good grounding system will also protect against static charge buildup.
Lighting will follow a second path if a strike occurs. The second path is down the lead-in wire and into the equipment that is connected to it. To protect against this lighting, surge protectors and static discharge devices are placed between the antenna and the receiving equipment. Check the installation manual for recommended lighting surge protectors and static discharge devices.
Planning the Installation
An antenna installation site must be safe, as previously mentioned. Keep a proper distance from power lines and telephone lines. For good reception, no obstruction should exit between the antenna and the receiving direction. The antenna will generally require a base, a mast, and a good supporting structure. The mast may be telescoping poles that are secured to a building or other structure.
If guy wires are used, there must be enough room around the mast to install them. Guy wires usually extend in three equally spaced directions. The wire should intercept the mast at 450 angles for proper support. The guy wires must be well anchored at the ground points where they attach to eyelets. Anchor the eyelets in concrete. This makes a very secure guy wire support system. Tighten the guy wires using turnbuckles.
Proper care should be exercised when running the leas-in line. Improper installation can result I trouble later on. Lead-in wire should be kept as short as possible. Twin-lead 300 ohms antenna wire, often used with TV and FM antennas, must be installed using standoff insulators. This wire should never touch metal. The metal will influence the transmission line’s characteristic impedance and cause attenuation and reflections. For area of high interference, substitute coaxial cable for the twin-lead wire. Coaxial cable does not require insulated standoffs. Taping it to the mast and running it along rain gutters makes foe the good installation.
When using coaxial cable instead of twin lead, remember that the antenna impedance must be matched to the transmission line. If the receiver does not permit direct connection of the coaxial cable, an impedance match must be made there also. Coaxial cable normally used with TV and FM antenna installation is RD-59/U. Its characteristic impedance is 75-ohms. Balun transformers match the antenna impedance and receiver input impedance, illustrated in figure 1. If the TV or FM receiver has a 75-ohms connection, then and antenna balun is all that is necessary.
Avoid running lead-in wires through windows. Run lines through a special tube that feeds the line into the building via the wall. Some installations may specify using conduct to protect the lead-in line from weathering. Once the line is in the building, distribution outlets can serve to distribute the signal to more than one receiver. If outlets are not used, cut off excess lead in. Do not curl it up behind the receiving equipment.