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Moxon antenna for the 20-meter band.The antenna is the faint rectangle of wires held in tension by the bent X-shaped support frame. Moxon antenna for the 2-meter band. The Moxon antenna or Moxon rectangle is a simple and mechanically rugged two-element parasitic array, single-frequency antenna. [1]
The thick, black, vertical line is the feed cable, ending in a small black box that contains a trimmer capacitor that with the gamma arm length, impedance matches the antenna feedpoint. 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.
A competing third criterion is the number and bandwidth of the frequenc(y/ies) that a single antenna intercepts or emits. A fourth design goal is to make the antenna directional: To project or intercept radio waves from only one vertical and / or horizontal direction as exclusively as possible.
The discone antenna has a useful frequency range of at least 10 to 1. [2] [3] When employed as a transmitting antenna, a properly constructed discone is just as efficient as an antenna designed for a more limited frequency range. The extra bandwidth comes from the controlled taper and large termination radius of the cone.
More common is electrical beam tilt, where the phasing between antenna elements is tweaked to make the signal go down (usually) in all directions. [1] This is extremely useful when the antenna is at a very high point, and the edge of the signal is likely to miss the target (broadcast audience, cellphone users, etc.) entirely.
The gain and input impedance of the antenna is dependent on the length of the whip element, compared to a wavelength, but also on the size and shape of the ground plane used (if any). A quarter wave vertical antenna working against a perfectly conducting, infinite ground will have a gain of 5.19 dBi and a radiation resistance of about 36.8 ohms.
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The vertical mast, isolated from the ground, or the vertical radiator wires, functions as a resonant monopole antenna. [2] [3] [4] At the low frequencies used, the height of the mast is much less than its resonant length, one quarter wavelength ( ), so it makes a very electrically short antenna; it has very low radiation resistance and without ...
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