File:Antenne gp vhf 3.jpg
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DescriptionAntenne gp vhf 3.jpg |
English: VHF ground plane antenna. This is a quarter-wave whip (monopole) antenna (white rod at top) with three grounded conductors projecting down from the base of the whip to form a "ground plane". Ground plane antennas have an omnidirectional radiation pattern, radiating equal signal strength in all azimuthal directions, with the radiated power maximum in a horizontal direction and decreasing with elevation angle to zero on the antenna axis. The ground conductors serve to increase radiated power in the horizontal direction. In many ground plane antennas the ground rods project horizontally from the base; in this antenna they are angled down to increase the input impedance of the antenna to 50 ohms, to match the 50 ohm coaxial cable feedline. Français : L'antenne ground plane ou GPA (Ground Plane Antenna) est un dipôle dans lequel on a remplacé la moitié par un « plan de sol », la moitié conservée étant normale à cette surface. Si le plan de sol est suffisamment grand, le demi-dipôle se comporte exactement comme un dipôle entier (type: dipôle demi-onde λ/2) car sa réflexion dans le plan de sol forme la partie manquante. Dans ce cas, son gain théorique est de 2,14 dBi (où les dBi sont des décibels avec un « i » ajouté pour rappeler qu'il s'agit d'un gain par rapport à une antenne isotrope), la longueur physique est environ égale au quart de la longueur d'onde de la fréquence sur laquelle l'antenne est accordée. Ces brins, disposés en cercle inclinés vers le bas ; en nombre de 3, ils constituent une surface conductrice de l'électricité, même si cette surface n'est pas parfaite pour être alimenté par un câble coaxial de 50 ohms . |
Date | |
Source | Own work • Self-photographed |
Author | F1jmm |
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Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.http://www.gnu.org/copyleft/fdl.htmlGFDLGNU Free Documentation Licensetruetrue |
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Date/Time | Thumbnail | Dimensions | User | Comment | |
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current | 22:43, 1 November 2010 | 744 × 1,140 (420 KB) | F1jmm (talk | contribs) | {{Information |Description= antenne Ground plane VHF |Source={{own}} |Date=2010-11-01 |Author=F1jmm |Permission= |other_versions= }} Category:Monopole antennas |
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Metadata
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot A420 |
Exposure time | 1/500 sec (0.002) |
F-number | f/4.5 |
Date and time of data generation | 14:38, 27 October 2010 |
Lens focal length | 14.411 mm |
Orientation | Normal |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop CS2 Windows |
File change date and time | 23:12, 1 November 2010 |
Y and C positioning | Centered |
Custom image processing | Normal process |
Exposure mode | Auto exposure |
White balance | Auto white balance |
Digital zoom ratio | 1 |
Scene capture type | Standard |
Exif version | 2.2 |
Date and time of digitizing | 14:38, 27 October 2010 |
Image compression mode | 3 |
APEX shutter speed | 8.96875 |
APEX aperture | 4.34375 |
APEX exposure bias | 0 |
Maximum land aperture | 4.34375 APEX (f/4.51) |
Metering mode | Pattern |
Flash | Flash did not fire, auto mode, red-eye reduction mode |
Color space | sRGB |
Focal plane X resolution | 12,085.106382979 |
Focal plane Y resolution | 12,085.106382979 |
Focal plane resolution unit | inches |
Sensing method | One-chip color area sensor |