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the upper half of a vertical full-wavelength loop antenna mounted on the ground (not to be confused with the visually similar but electrically different half-square antenna described below, under array antennas, [t] nor to be confused with the halo antenna, described next). The full loop is cut at two opposite points along its perimeter, and ...
An antenna such as the one described above is usable for both local and medium-long-distance communication across a frequency range of about 1:6 . For example, an antenna for the lower portion of shortwave (say, 3–18 MHz) will be roughly 33 m (110 feet) long, with conductors spaced 1 m (3.3 feet). For the higher portion of shortwave (5–30 ...
The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.
A resonant trap L2/C2 eliminates the common mode current at the lower end of the antenna. [2] The L1/C1 components (see the illustration) matches the feedline impedance of 50 Ω to the 100 Ω system of the antenna. Despite the fact that the feedpoint for the antenna is applied at the base, electrically it is a centre fed dipole.
German physicist Heinrich Hertz first demonstrated the existence of radio waves in 1887 using what we now know as a dipole antenna (with capacitative end-loading). On the other hand, Guglielmo Marconi empirically found that he could just ground the transmitter (or one side of a transmission line, if used) dispensing with one half of the antenna, thus realizing the vertical or monopole antenna.
A halo antenna, or halo, is a center-fed 1 / 2 wavelength dipole antenna, which has been bent into a circle, with a break directly opposite the feed point. The dipole's ends are close, but do not touch, and the ends on either side of the gap may be flared out to form a larger air gap capacitor , whose spacing is used to fine-adjust the ...
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Often random wire antennas are also (inaccurately) referred to as long-wire antennas.There is no accepted minimum size, but actual long-wire antennas must be greater than at least a quarter-wavelength ( 1 / 4 λ) or perhaps greater than a half ( 1 / 2 λ) at the frequency the long wire antenna is used for, and even a half-wave may only be considered "long-ish" rather than "truly ...
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