Thursday, March 14, 2019

Work low band HF DX with the half-square

Earlier this month we featured the bobtail curtain.  This is an effective antenna for low HF band DXing.  The main drawback is its length.  At 1 wavelength this is too much for most peoples' backyards.

If you like the concept but don't have the space, consider the half-square instead. It fits in the same space as a flat top half wavelength dipole but puts out a vertically polarised low angle signal. This makes it a good DX antenna for bands like 40 or 80 metres.  Radiation direction is towards and away from you.
The drawing above shows the half-square fed in a top corner (doesn't matter which one) with coaxial cable. This should be brought away from the antenna to avoid interaction. Or you can keep both corners joined and feed at the bottom if you have an antenna coupler or tuned circuit that can handle the high impedance.  Although it will no longer operate as a half square, an external coupler allows the antenna to operate efficiently on other bands as an end-fed.

The bottom of the vertical elements of the half square can be quite low to the ground.  Only 1 or 2 metres is OK. This low height requirement makes the half square more attractive than many other low band HF antennas, especially for DX working.  Construction is super simple with two appropriately spaced supports. Just keep it as symmetrical as possible.

Interested? There's more in these articles and videos:

* AF6EF's half square instructions
* N4DJ's 3.5 MHz half square (video)
* N6LF's article on using half squares for DX (pdf)
* Commercially available 14 MHz half square
* Half square on 10 MHz (one of my videos)
* Waters edge portable DX 14 MHz half square (another of my videos)

PS: Enjoy these well-reviewed books on various amateur radio topics. They're available for under $US 5 each in electronic form. Or you can get them in paperback. Visit VK3YE Radio Books to find out more. 

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