W8WWV - Hex Array - Conclusion

Greg Ordy


While all conclusions won't be in for some time, there are some lessons that I have learned to this point. This list will grow over time.

Accurate Impedance Measurements

The whole process of building and adjusting a phased array, and probably any antenna for matter, is made much easier if you can make accurate impedance measurements. By accurate I mean 0.1 Ohm resolution with the ability to distinguish positive reactance from negative reactance.

Solutions have provided either low accuracy (antenna analyzers), low convenience (traditional impedance bridges), or high cost (lab grade impedance analyzers). Recently, I have started to work with the VNA (Vector Network Analyzer) project designed by Paul, N2PK. This device promises excellent accuracy, additional functionality, and low cost. If it has a down side, it is that it is currently only available if you are willing to buy the parts and assemble a board that uses surface mount devices.

Here are some of the places where impedance measurements are used in this application area:


Loss is waiting around every corner and will pounce at a moments notice. Unless you are careful, it's very easy to give back 1/3 to 1/2 of the theoretical gain in your array through loss. Look for loss in element loading devices, radial systems (ground loss), transmission lines connecting the elements to the phasing box, and within the phasing box itself.

Generally speaking, loss can be more easily reduced by using full size elements, and relatively wider spacing. It is also important to have the best possible radial system, since that will reduce the ground loss.

Trust but Verify

Given all of the factors which influence the array, and the accuracy of impedance measurements, the uncertain uniformity of transmission lines, and the tolerance and Q of phasing network components, it would seem to be impossible to design and build a vertical array without a final adjustment to achieve the desired currents. After all of the expense and work to design and build the array, don't skip the final step. Get some current probes and a multiple channel oscilloscope and verify the desired current ratios.


As I write this section, I've used the array for several months, and through the first half of the more active winter season. On 40 meters, the performance, by my standards, is very good. Through comparisons with my separate vertical, which was previously compared against my phased 40 meter delta loops, the Hex Array clearly has a few dB more gain. On reception, the antenna is very quiet with the 60 degree beamwidth. I can listen to west coast stations and effectively knock down the strong European broadcast stations.

Having the ability to change direction in a fraction of a second is also very nice. I can easily select between the short and long path, if it's at a time when that's a question. I can also follow conversations that span the globe. One of my favorites is to listen to G stations in Great Britain work ZL stations in New Zealand, at G sunrise and ZL sunset, which is the middle of the night for me. I can quickly switch directions and follow the QSO. I could not rotate a traditional Yagi that quickly.

80 meter performance is a little less impressive. The standard here in Ohio is to break through the wall of east coast stations that have a geographic advantage into Europe, and the long path into Asia at our sunset. There are many fine stations on the east coast, and they clearly will work the DX before me. On the other hand, they suffer going to the west. I remember a recent morning when I worked a KL station in Alaska with a very loud signal. I could hear many east coast stations calling, and the KL could barely copy them, working very few. You have to work very hard on your antenna system  to overcome geography. This is not to say that I don't work stations with ease. It's just a sense that the size of my club is a little smaller on 80 meters as opposed to 40 meters.

As expected, for local stations, my inverted Vee outperforms the Hex Array, often by 15 dB or more. That's fine, and shows that local communication (several hundred miles) happens at a very high take-off angle, which is what the Vee does best. Past about 600 miles, however, the Hex Array starts to perform better.

On both bands the real fun is listening, even more than transmitting. I can certainly hear very well with this array.

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Last update: Sunday, January 04, 2004 03:41:54 PM
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