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A short antenna pole next to a house Multiple Yagi TV aerials. Antennas are commonly placed on rooftops and sometimes in attics. Placing an antenna indoors significantly attenuates the level of the available signal. [19] [20] Directional antennas must be pointed at the transmitter they are receiving; in most cases great accuracy is not needed ...
A basic goal of antenna design is to make the currents add up to a maximum at the point where the energy is tapped off. To do this, the antenna elements are sized in relation to the wavelength of the radio signal, with the aim of setting up standing waves of current that are maximized at the feed point.
A broadcast transmitter is an electronic device that radiates radio waves modulated with information content intended to be received by the general public. Examples are a radio broadcasting transmitter which transmits audio (sound) to broadcast radio receivers (radios) owned by the public, or a television transmitter, which transmits moving images to television receivers (televisions).
Beta waves, or beta rhythm, are neural oscillations (brainwaves) in the brain with a frequency range of between 12.5 and 30 Hz (12.5 to 30 cycles per second). Several different rhythms coexist, with some being inhibitory and others excitory in function.
This antenna has fixed cell delays, configured by different cutout sizes in each cell, as can be seen in the top-right inset. Larger cutouts produce the dark rings visible in the overview. A reflectarray antenna (or just reflectarray) consists of an array of unit cells, illuminated by a feeding antenna (source of electromagnetic waves).
A time-domain reflectometer; an instrument used to locate the position of faults on lines from the time taken for a reflected wave to return from the discontinuity.. A signal travelling along an electrical transmission line will be partly, or wholly, reflected back in the opposite direction when the travelling signal encounters a discontinuity in the characteristic impedance of the line, or if ...
The antenna is most sensitive to radio waves coming from the right, parallel to the antenna's axis. All the elements are usually mounted on a metal beam or bracket along the antenna's central axis. Although sometimes the parasitic elements are insulated from the supporting beam, often they are clamped or welded directly to it, electrically ...
The moving red lines show the wavefronts of the radio waves emitted by each element. The individual wavefronts are spherical, but they combine in front of the antenna to create a plane wave. The phase shifters delay the radio waves progressively going up the line so each antenna emits its wavefront later than the one below it.