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490 MHz Collinear Helical HPOL OMNI-PLUS
490 MHz Horizontally Polarized Collinear (Axial Mode) Helical Antennas  were analyzed using 4NEC2.

1) 15-Turns above a 36x36-in Square Grid Ground Plane: It is an OMNI-PLUS type
[with and AT LEAST 0 dBd Gain = 2.15 dBi in ALL directions].... and significantly MORE in some directions.

In order to provide improved Look Down Angle Coverage, the Antenna would be mounted Upside-Down.

Azimuthal Gain Min = 4.2 dBi and Gain Max = 6.3 dBi with SWR (200-ohms) = 1.4 (very Flat).
A 4:1 Balun would be used to connect to 50-ohm Coax and Transmitter.

2) T.B.D.
10 Mar 201613 items2098 visitsAlbum by holl_ands
Enlarge photo 1enlarge 176KB, 842x1024
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490 MHz H-Pol 15-Turn Helical + Square Grid
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490 MHz H-Pol 15-Turn Helical + Square Grid
Front View
[1 Large Square = 12.5-inches]
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490 MHz H-Pol 15-Turn Helical + Square Grid
Top View
[1 Large Square = 5-inches]
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490 MHz H-Pol 15-Turn Helical + Square Grid
3D Gain for Horizontal Polarization
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490 MHz H-Pol 15-Turn Helical + Square Grid
3D Gain for Vertical Polarization
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490 MHz H-Pol 15-Turn Helical + Square Grid
3D Gain for Total Polarization
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490 MHz H-Pol 15-Turn Helical + Square Grid
Raw Gain Maximized near 490 MHz
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490 MHz H-Pol 15-Turn Helical + Square Grid
UHF SWR (200-ohms) = 1.4 across Entire Band
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490 MHz H-Pol 15-Turn Helical + Square Grid
UHF Impedance = 240 - 250 ohms
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490 MHz H-Pol 15-Turn Helical + Square Grid
Azimuthal Pattern at 490 MHz
Raw Gain = 4.0 to 6.3 dBi
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490 MHz H-Pol 15-Turn Helical + Square Grid
Elevation Gain Pattern
Worst Case -23.6 dBi Null at Elev=20-deg
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490 MHz H-Pol 15-Turn Helical + Square Grid
Side View
[1 Large Square = 12.5-inches]
Enlarge HTML Document 13enlarge 151KB, 791x1024
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490 MHz H-Pol 15-Turn Helical + Square Grid
EVAL *.html Performance File incl. 4NEC2 File
which includes Dimensions.
 
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