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An NVIS antenna configuration is a horizontally polarized (parallel with the surface of the earth) radiating element that is from 1 / 20 th wavelength to 1 / 4 wave above the ground. The optimum height of such an antenna is about 1 / 4 wavelength, and high angle radiation declines only slightly for heights up to about ...
Significant wave height H 1/3, or H s or H sig, as determined in the time domain, directly from the time series of the surface elevation, is defined as the average height of that one-third of the N measured waves having the greatest heights: [5] / = = where H m represents the individual wave heights, sorted into descending order of height as m increases from 1 to N.
The directivity is defined as the ratio of the maximum signal strength S radiated by the antenna to the signal strength S iso radiated by the isotropic antenna = Since the directional antenna radiates most of its power into a small solid angle around the z-axis its maximum signal strength is much larger than the isotropic antenna which spreads ...
44–51, 54–68 MHz: Band I Television (channels 1–3) 87.5–108 MHz: Band II Radio; 118–137 MHz: Airband for air traffic control, AM. 108–117.975 MHz: Air navigation beacons VOR and ILS; 121.5 MHz is an emergency frequency; 144–148 MHz: Amateur radio 2-meter band; 156–162.2 MHz: Marine radio; 174–230 MHz: Band III Television ...
It is therefore widely used by radio amateurs with limited space. [3] In particular for low frequencies this antenna form is interesting. [4] 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]
If used for transmitting, the resistor makes traveling-wave antennas inefficient, since the resistor absorbs any radio wave after the wave has made a single pass through the antenna wire, as opposed to a resonant antenna in which radio waves cycle back-and-forth several times, giving the signal multiple opportunities to radate.
The radiation resistance ( ) is conventionally defined as the value of electrical resistance that would dissipate the same amount of power as heat, as is dissipated by the radio waves emitted from the antenna. [1] [3] [4] From Joule's law, it is equal to the total power radiated as radio waves by the antenna, divided by the square of the RMS ...
Typical feeder loops are 1 / 8 to 1 / 5 the size of the antenna's main loop, which gives transform ratios of 64:1 to 25:1, respectively. Adjusting the proximity and angle of the feeder loop to the main loop, and distorting the feeder's shape, both make small-to-moderate changes to the transform ratio, and allows for fine ...