Friday, 4 February 2011

4m Halo Antenna By Gabriele Antonielli,IZ5HQB.

Photo 1
The halo is an omni-directional antenna with horizontal polarization. This is practically a horizontal loop, namely a half-wave folded dipole, with its endings slightly separated ,(Photo 1). The feeding is done through a system called gamma-match with the condenser obtained by inserting the central core of RG58 cable including the insulator, inside the aluminium tube that forms the gamma-match.
Based on a commercial model, it was reproduced using aluminium tubes from 4 and 6 mm (sold in DIY stores). The boom (H) is made with an aluminium profile 10/10 mm square section. If you are using anodized aluminium, remember that it should be grinded at all points of contact for an improved electrical conduction. 
The dimensions below can be modified during implementation to match the materials used in construction. But the important thing is to maintain the distance between E-F and B-C, (Photo 2 and Photo 3).
Photo 2
Photo 3
The E-F segment is composed of an insulating material,(PVC or wood).
The dipole is connected to the boom in the A-B side, through a screw with an insulator between the boom and the dipole,(Photo 4).
Photo 4
The gamma-match (C-G) (photo 4) is electrically connected at the point C with the dipole and isolated in G by a distance from the PVC boom. At this point it is connected the connector cable with the ground attached to the boom, while the central core is soldered of the wire (RG58) where the tuner-capacitor is done,(Photo 5).
Photo 5

For calibration can be used by a simple SWR meter, find the lowest point of SWR by inserting or removing the wire inside the tube (C- G gamma-match)(Photo 5). When the above dimensions has been achieved with SWR values of 1:1 from 70,100 to 70,300.
Finished Antenna

Finished Antenna

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