Half-Square Antenna

Before: dipole.

After: Half-square

A half-square exhibits a low take-off angle without the need for ground radials or counterpoise wires. One way to picture it is to imagine two 1/4 wavelength verticals spaced one-half wavelength apart fed in-phase. This produces a bi-directional "8" pattern broadside to the array. The horizontal wire across the top is the 1/2 wavelength phasing line between the tops of the two vertical legs, and does not contribute much to the radiation pattern. When electromagentically excited, current maxima appear at the top corners and voltage maxima at the bottoms of the two vertical llegs, which must be kept out of reach of humans and animals. The aerial is tuned to resonance by adjusting the lengths of the vertical legs rather than by adjusting the horizontal "phasing" line, which should be kept to the dimensions provided by mathematical formulae. You can cram it into limited-spaces because it is not finicky with regard to the proportions of its dinensions. For example, if you don't have the 36 to 40 feet of vertical height it requires, you can slope the legs off to the same side, or tuck them towards each other under the aerial without depreciating performance.

The 7 MHz Half-Square Vertical length ~33 to 38 feet • Spaced ~66'

Suspension Height ~ 36 to 40' • 50 Ohm feedpoint impedance

Can be directly fed at either corner or through parallel circuit at bottom

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To convert a 40 meter dipole into a half-bobtail, don't do anything to the feedpont connection. Just add 1/2 wavelength of wire to either of the legs. If you are not feeding your dipole through a balun, splic the extra wire to the leg that is connected to the center conductor of the coax after removing the end insulator. Slip the insulator back on and slide it down 1/4 wavelength (33' to 38'). You can secure the insulator by crimping the wire corner with a cable tie; if you twist it around the insulator, it will untwist when the array is tensioned. This insulator now serves as one of the corner supports. Attach another insulator to the end of the extra wire. This insulator serves as one of the end supports, with the feedpoint insulator serving as the other one. This completes the conversion of the dipole into a half-bobtail!

How to Convert a Dipole into a Half-Square

1/2 wavelength of wire is spliced onto a dipole. 

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You now have a DX antenna that looks like an inverted "U". The two vertical legs drop down until their end insulators hover 3 to 6 feet above the ground to which they are staked with bungie cords. The height of the aerial is between 36 to 40 feet. Right now we are testing it on 40 Meters at night. On February 12, 2018, the contraption worked into Europe until Noon (1100 UTC). Incredible for a piece of wire without any radials! 

Half-Square Working Europe Until Noon

February 12, 2018 • 7 Mhz

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