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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 ...
The AT&T receiving Beverage antenna (left) and radio receiver (right) at Houlton, Maine, used for transatlantic telephone calls, from a 1920s magazine. The Beverage antenna or "wave antenna" is a long-wire receiving antenna mainly used in the low frequency and medium frequency radio bands, invented by Harold H. Beverage in 1921. [1]
Inverted-L antenna with counterpoise, in a powerful amateur radio station, Colorado, 1920. The counterpoise is the lower grid of horizontal wires, suspended below the antenna. The largest use of counterpoises is in transmitters on the low frequency (LF) and very low frequency (VLF) bands, as they are very sensitive to ground resistance. [2]
Assuming the building is about 20 feet tall, the length of wire seems to be on the order of 100 feet long – too short to be an HF Beverage antenna. Random wire antenna Moxon (1993) describes the random-wire antenna as an "odd bit of wire". [15] [page needed] It is the typical informal antenna erected for receiving shortwave and AM radio.
In antennas built for frequencies near or below 600 kHz [b], the length of an antenna's wire segments is usually shorter than a quarter wavelength [c] [ 1 / 4 λ ≈ 125 m (410 feet) [c] at 600 kHz [b]], the shortest length of unloaded straight wire that achieves resonance. [5]
The angle of the slope is usually between 45°–60° and the lower end of the wire is at least 1 ⁄ 6 wavelength above the electrical ground. [3] A sloper is typically fed with a coaxial cable in the center, at the top of the center support mast. At least 1 ⁄ 4 of the wavelength of feedline must be at 90° angle to the antenna. [3]
The cone: The length of the cone should be a quarter wavelength of the antenna's lowest operating frequency. [2] The cone angle is generally from 25 to 40 degrees. The insulator: The disc and cone must be separated by an insulator, the dimensions of which determine some of the antenna's properties, especially on near its high frequency limit.
The relationship between the lengths is a function known as tau. Sigma and tau are the key design elements of the LPDA design. [1] [2] The radiation pattern of the antenna is unidirectional, with the main lobe along the axis of the boom, off the end with the shortest elements.
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