Feed Line

In a radio antenna, the feed line is the cable or other transmission line that connects the antenna with the radio transmitter or receiver. In a transmitting antenna, it feeds the radio frequency (RF) current from the transmitter to the antenna, where it is radiated as radio waves. In a receiving antenna it transfers the tiny RF voltage induced in the antenna by the radio wave to the receiver. In order to carry RF current efficiently, feed lines are made of specialized types of cable called transmission line. The most widely used types of feed line are coaxial cable, twin-lead, ladder line, and at microwave frequencies, waveguide.

Particularly with a transmitting antenna, the feed line is a critical component that must be adjusted to work correctly with the antenna and transmitter. Each type of transmission line has a specific characteristic impedance. This must be matched to the impedance of the antenna and the transmitter, to transfer power efficiently to the antenna. If these impedances are not equal it can cause a condition called standing waves on the feed line, in which the RF energy is reflected back toward the transmitter, wasting energy and possibly overheating the transmitter. This adjustment is done with a device called an antenna tuner in the transmitter.

Read more about Feed Line:  Twin Lead, Coaxial Cable, Wave Guide, Feed Line Characteristics

Other articles related to "feed line, line":

Feed Line Characteristics
... This is a comparison of a few common feed line characteristics ... type impedance velocity factor twin-lead 300 82% ladder line 450, 600 95% coax 50, 75 66% ...
Antenna (radio) - Parameters - Impedance
... the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc.) ... the source, forming a standing wave in the feed line ... The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer ...
Standing Wave Ratio - Practical Implications of SWR
... When a transmitter is connected to an antenna by a feed line, the impedance of the antenna and feed line must match exactly for maximum energy transfer from the feed line to the antenna to ... Matching the impedance of the antenna to the impedance of the feed line is typically done using an antenna tuner ... The tuner can be installed between the transmitter and the feed line, or between the feed line and the antenna ...

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