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In telecommunications, the effective height of an antenna is the height of the antenna's center of radiation above the ground. In low- frequency applications involving loaded or nonloaded vertical antennas, the effective height is the moment of the current distribution in the vertical section, divided by the input current.
In antenna theory, radiation efficiency is a measure of how well a radio antenna converts the radio-frequency power accepted at its terminals into radiated power. Likewise, in a receiving antenna it describes the proportion of the radio wave's power intercepted by the antenna which is actually delivered as an electrical signal.
The height above average terrain for VHF and higher frequencies is extremely important when considering ERP, as the signal coverage (broadcast range) produced by a given ERP dramatically increases with antenna height. Because of this, it is possible for a station of only a few hundred watts ERP to cover more area than a station of a few ...
Height above average terrain (HAAT), or (less popularly) effective height above average terrain (EHAAT), is the vertical position of an antenna site above the surrounding landscape. HAAT is used extensively in FM radio and television , as it is more important than effective radiated power (ERP) in determining the range of broadcasts ( VHF and ...
Efficiency is the ratio of power actually radiated by an antenna to the electrical power it receives from a transmitter. A dummy load may have an SWR of 1:1 but an efficiency of 0, as it absorbs all the incident power, producing heat but radiating no RF energy; SWR is not a measure of an antenna's efficiency.
If under 250 W at night, the antenna must be efficient enough to radiate more than 140.82 mV/m at 1 km. C (formerly IV) — local unlimited-time stations — 250 W to 1 kW, 24 hours. Class C stations that were licensed at 100 W are grandfathered. Rare Class Cs operate with directional arrays, such as KYPA and KHCB.
Although these antennas are enormous compared to a human, at 15 kHz the antenna height is still only about 0.015 wavelength, so paradoxically, huge VLF antennas are electrically short. From the table above, a 0.015 λ monopole antenna has a radiation resistance of about 0.09 Ohm.
It can be used for base-station antenna heights ranging from 30–1000 m. Okumura developed a set of curves giving the median attenuation relative to free space (A mu), in an urban area over a quasi-smooth terrain with a base station effective antenna height (hte) of 200 m and a mobile antenna height (hre) of 3 m. These curves were developed ...