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PowerPedia:Antenna - PESWiki (8885 words) |
 | Antennas are primarily designed for transmission of radio wave energy through free space or any space where the movement of energy in any direction is substantially unimpeded, such as interplanetary space (such as the interplanetary medium or interstellar medium), the atmosphere, the ocean (and other large bodies of water), or the Earth. |
| Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. |
| The "polarization" of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation. |
| Combination outdoor daytime/nighttime advertising billboard - Patent 5570138 (2920 words) |
| A combination outdoor daytime/nighttime outdoor advertising display billboard is provided having a surface for displaying a fixed image during the daytime and a projection screen apparatus which automatically unrolls to present a projection screen for displaying a projected image during the nighttime. |
| A billboard bearing a fixed advertising image is hinged along one edge to enable it to be swung into close adjacent contact with the translucent screen for viewing from the outside during daylight hours. |
| In this manner, the billboard 12 may be used in the conventional manner during the daytime as it is unaffected by the presence of the projection screen apparatus 30. |
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