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2. Helical antenna - Wikipedia

   en.wikipedia.org/wiki/Helical_antenna

   This means that for example a ⁠ 1 / 4 ⁠ wave antenna at 27 MHz is 2.7 m (110 inches; 8.9 feet) long and is physically quite unsuitable for mobile applications. The reduced size of a helical provides the same radiation pattern in a much more compact physical size with only a slight reduction in signal performance.

3. Near vertical incidence skywave - Wikipedia

   en.wikipedia.org/wiki/Near_Vertical_Incidence...

   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 ...

4. Random wire antenna - Wikipedia

   en.wikipedia.org/wiki/Random_wire_antenna

   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 ...

5. Antenna measurement - Wikipedia

   en.wikipedia.org/wiki/Antenna_measurement

   Antenna directivity is the ratio of maximum radiation intensity (power per unit surface) radiated by the antenna in the maximum direction divided by the intensity radiated by a hypothetical isotropic antenna radiating the same total power as that antenna. For example, a hypothetical antenna which had a radiated pattern of a hemisphere (1/2 ...

6. Antenna (radio) - Wikipedia

   en.wikipedia.org/wiki/Antenna_(radio)

   For instance, if a radio wave passing a given location has a flux of 1 pW / m 2 (10 −12 Watts per square meter) and an antenna has an effective area of 12 m 2, then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts RMS at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all ...

7. Monopole antenna - Wikipedia

   en.wikipedia.org/wiki/Monopole_antenna

   Since a half-wave dipole has a gain of 2.19 dBi and a radiation resistance of 73 Ohms, a quarter-wave (⁠ 1 / 4 ⁠ λ) monopole will have a gain of 2.19 + 3.0 = 5.2 dBi and a radiation resistance of about 36.5 Ohms. [13] The antenna is resonant at this length, so its input impedance is purely resistive.