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Gayan Sameera, profile picture
Uploaded byGayan Sameera
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Adjustable Ground Plane Antenna

This document describes an adjustable ground plane antenna designed for VHF base station use between 144-174 MHz. It has an aluminum mounting tube with a radiating element and radials for omnidirectional radiation. It can handle over 200 Watts of power and has a SWR below 1.5:1 across its adjustable frequency range. The antenna uses aluminum pipes and coaxial cable to construct the radiating element, radials, and feedline in a way that makes the assembly waterproof.

Engineering◦
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2 | P a g e 4s6ggs C Right adjustable ground plane antenna designed primarily as a VHF base station antenna when a high gain antenna is not required or justified. As it is adjustable over the entire VHF high band 144 to 174MHZ The antenna is constructed of an aluminium mounting tube with the radiating element enclosed by a UV stabilis,piece design. The antenna is DC grounded for lightning protection and reduction of static noise. omnidirectional unity gain adjustable ground plane quarter wave radiating element with the radials acting as a counterpoise. Specifications  Impedance at resonance: 50 ohms  Resonant Frequency: 144-174 MHz (adjustable)  Frequency range with SWR below 1.1.5 MHz (adjustable)  Power handling capability: greater than 200 Watts  Radiation Polarity: vertical  Directionality: omnidirectional  Angle of maximum radiation: approximately 45 degrees from horizontal Materials  1120mm length of 38mm T2mm Aluminum pipe, cut to resonance 1Nos. Radiator  137mm length of 38mm T2mm Aluminum pipe, cut to resonance 1Nos Radiator  1131mm length of 19mm T 2mm Aluminum pipe, cut to resonance 2Nos Radials  38mm Aluminum pipe end cap 1 No’s  38mm I.D. compression pipe clamp 2 no’s for Radials  RG-8 or RG-213 50 ohm coax cable 980mm 1Nos feed point matching  RG-8 or RG-213 50 ohm coax cable 1500mm 1Nos feed point fat tx rx  PVC tube ID 38mm T 3mm L152mm insulator
3 | P a g e 4s6ggs C Right Construction The antenna is constructed around a standard 38mm diameter aluminum radial elements have been attached with 19mm diameter elements The radiating element is fitted to coax center pin and positioned with two part coax matching Marine grade silicon to make to assembly water proof.
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10 | P a g e 4s6ggs C Right  RG-8 or RG-213 50 ohm coax cable 980mm 1Nos feed point matching  RG-8 or RG-213 50 ohm coax cable 1500mm 1Nos feed point fat tx rx Joint cox
11 | P a g e 4s6ggs C Right The actual impedance of the antenna at its center feed point varies with frequency and antenna height. The transmission line is a balanced conductor pair with a 50-Ω impedance. Coax cable with a 50- Ω characteristic impedance (Zo) Coax is an unbalanced line since RF current will flow on the outside of the coax shield, creating some undesirable induced RF in nearby devices, although the antenna will work well enough. The best feed method is to use FEED POINT FOR TX /RX Cox center FEED POINT FOR TX /RX Cox Outer
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13 | P a g e 4s6ggs C Right Feed for TX /RX Feed for Machine Machin Feed for TX /RX center Feed for TX /RX outer Feed for Mac outer Feed for Mac center Feed for Mac center
14 | P a g e 4s6ggs C Right Feed for Mac center Feed for Mac center Feed for TX /RX center
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