Amateur Radio (G3TXQ) - Understanding the HexBeam

I like the HexBeam - it's an innovative design, and to my eyes (if not the XYL's) looks more elegant than those ugly aluminium alternatives :) It's not a "magic" antenna - other designs beat it for gain, front-to-back ratio and bandwidth; however, if you want an antenna that can be "multi-banded", exhibits useful gain and directivity, is very lightweight, has a small turning radius, and lends itself readily to "Do It Yourself" construction, the HexBeam should be very high on your list of options.

I am indebted to Leo (K4KIO) and Holger (DL7IO) for producing websites that first excited my interest in the HexBeam. Leo has also been very supportive in my efforts to get a better understanding of how the HexBeam works - at the last count we had exchanged 474 emails!

The defining feature of the HexBeam is its shape. In many ways it behaves like a conventional 2-element Yagi, but the Driver and Reflector elements are bent into a "W" shape to conserve space. It is usually constructed of wire elements strung onto a support structure of fibre-glass spreaders. By "bowing" the spreaders, the elements for several amateur bands can be accommodated on the same support structure, in much the same way as a cubical quad antenna. This approach allows a multiband beam to be constructed with a turning radius about half that of the corresponding Yagi.

Don't miss the sections on a new Broadband Hexbeam which I developed during Autumn 2007; it provides a significant improvement in bandwidth for a modest increase in size. It was the subject of an article I wrote for the December 2007 edition of Antennex - the on-line magazine for antenna experimenters.

Although this site contains some photographs of my own HexBeam, it does not provide detailed constructional information. If you need guidance on making one, you should visit Leo's (K4KIO) website where you will find lots of practical information and advice, including a recommended set of dimensions for both the new Broadband design and the Classic design. If you find it difficult to source any of the materials, visit Holger's website - he can supply most of the parts. If you are attracted by the idea of a HexBeam but don't want to build one, a commercial version is available from Mike Traffie; and if you want to keep up to date with what's going on in the HexBeam world you should take a look at the Yahoo special interest group.

These HexBeam pages are my attempt to "de-mystify" the antenna. They are the result of many hours simulation of various designs using EZNEC, backed up by practical measurements. Hopefully they will give you a detailed insight into how the antenna works, will encourage you to construct one for yourself, and will help you to get the best out of it.

Unless otherwise stated, performance parameters quoted are for a Free Space, zero-loss, environment and Gains are quoted referenced to an Isotropic radiator (dBi). This approach is convenient because it allows antennas to be evaluated on a "level playing field" without needing to consider the effect of the local environment (height above ground, ground conductivity, wire composition etc); it is also consistent with the way most commercial antenna manufacturers choose to quote their data. However the "real world" will modify the results that you get in practice. For example, I have found that on-air testing of F/B ratios with DX stations consistently produces figures that are around 10dB higher than predicted by Free Space modelling. This does not invalidate Free Space modelling - but it means you have to be careful how you interpret the results!

Dimensions on this website are quoted in inches - folk who prefer the metric system can multiply by 2.54 to get the equivalent in centimetres. You should also note that many HexBeam enthusiasts - me included - tend to measure dimensions from the centre post to the tip of an element; so when I quote a Reflector as 219" long, the total length of the Reflector is 438"!

Many of the features discussed in these pages are illustrated by investigating the performance of a "benchmark" 20m monoband HexBeam. For reference, this model has the following dimensions:

• Driver (half) length: 218.6"
• Reflector (half) length: 221.8"
• Driver end insulator: 6.7"
• Reflector end insulator: 4.3"
• Wire: #16 bare copper

Although 20m is used for the example, the results scale linearly to other bands.

I suggest that you work your way in sequence through these pages if you are unfamiliar with the HexBeam. Although much of the discussion in these pages is based on the practical experiences of myself and others, much is also the result of simulating the HexBeam's performance using EZNEC; I have therefore included two pages on modelling the HexBeam which seek to justify the results obtained through simulation.

Finally: Don't let the volume of data on these HexBeam pages put you off having a go at constructing one - K4KIO's website has step-by-step instructions - I'm sure you will be pleased with the results.

I would welcome questions or comments on these HexBeam pages. Mail me at: hexbeam{at}karinya.net