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Yagis have been built with 40 directors [3] and more. [11] The bandwidth of an antenna is, by one definition, the width of the band of frequencies having a gain within 3 dB (one-half the power) of its maximum gain. The Yagi–Uda array in its basic form has a narrow bandwidth, 2–3 percent of the centre frequency. [4]
A single ground wire can provide antenna gain in the 3–6 dB range. This is a reflector element used to form a 2-element Yagi beam antenna. The wire length for the reflector element is 5% longer than the dipole-driven element positioned above it. The dipole is located at a distance of 0.15 wavelengths above the reflector element.
Very high frequency (VHF) is the ITU designation [1] [2] [3] for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.
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]
In October 1866 Mahlon Loomis demonstrated communication between two grounded 183-meter (600-foot) wire aerials supported by kites on mountaintops 22 kilometres (14 miles) apart. [32] When one aerial wire was touched to a grounded contact, currents of atmospheric electricity in it apparently generated radio waves which induced currents in the ...
On October 10, the Third National Radio Conference made three shortwave bands available to U.S. amateurs [8] at 80 meters (3.75 MHz), 40 meters (7 MHz) and 20 meters (14 MHz). These were allocated worldwide, while the 10-meter band (28 MHz) was created by the Washington International Radiotelegraph Conference [ 9 ] on 25 November 1927.
A long-range seismic sensor network was used during the Andean Seismic Project in Peru. A multi-hop span with a total length of 320 kilometres (200 miles) was crossed with some segments around 30 to 50 kilometers (19 to 31 miles). The goal was to connect to outlying stations to UCLA in order to receive seismic data in real time. [2]
Patch antenna gain pattern. A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only.