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Summary
DescriptionAntenne gp vhf 2.jpg |
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 .
English: VHF ground plane antenna. This is a quarter-wave whip (monopole) antenna (white rod at top) with three grounded quarter-wave 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 to twice the gain of a dipole, or 5.19 dB. If the ground plane wires extended out horizontally from the base of the monopole the impedance would be half that of the dipole, or 36.5 ohms. However the downward slant of the ground plane wires serves to increase the antenna impedance, so the antenna is a good match for the 50 ohm coaxial cable feedline. |
Date | |
Source | Own work • Self-photographed |
Author | F1jmm |
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current | 22:37, 1 November 2010 | 1,036 × 1,312 (743 KB) | F1jmm | {{Information |Description=Antenne gp vhf |Source={{own}} |Date=2010-11-01 |Author=F1jmm |Permission= |other_versions= }} Category:Dipole antennas |
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot A420 |
Exposure time | 1/200 sec (0.005) |
F-number | f/5 |
Date and time of data generation | 14:38, 27 October 2010 |
Lens focal length | 17.3 mm |
Orientation | Normal |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop CS2 Windows |
File change date and time | 23:10, 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 |
Shutter speed | 7.65625 |
APEX aperture | 4.65625 |
Exposure bias | 0 |
Maximum land aperture | 4.65625 APEX (f/5.02) |
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 |
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