Chapter 19 Table 19.1 Characteristics of Commonly Used Transmission Lines
Transmission Lines 19 power is rarely generated right where it will be used. A transmitter and the antenna it feeds are a good example. To radiate effectively, the antenna should be high above the ground RF and should be kept clear of trees, buildings and other objects that might absorb energy. The transmitter, however, is most conveniently installed indoors, where it is out of the weather and is readily accessible. A transmission line is used to convey RF energy from the transmitter to the antenna. A transmission line should transport the RF from the source to its destination with as little loss as possible. This chapter was written by Dean Straw, N6BV. There are three main types of transmission lines used by radio amateurs: coaxial lines, open-wire lines and waveguides. The most com- mon type is the coaxial line, usually called coax. See Fig 19.1A. Coax is made up of a center conductor, which may be either stranded or solid wire, surrounded by a concentric outer conductor. The outer con- ductor may be braided shield wire or a metallic sheath. A flex- ible aluminum foil is employed in some coaxes to improve shielding over that obtainable from a woven shield braid. If the outer conductor is made of solid aluminum or copper, the coax is referred to as Hardline. The second type of transmis- sion line utilizes parallel con- Fig 19.1—In A, coaxial cable transmission line connecting signal ductors side by side, rather than generator having source resistance Rg to reactive load Ra ± jXa, the concentric ones used in where Xa is either a capacitive (–) or inductive (+) reactance.
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