[TowerTalk] Tuning raised radial verticals

[Dan Maguire]

This is what a model of N2WQ's 4-sq might look like, with each of the four elements in the shape of an "L" (68.5 ft vertical, ~70 ft horizontal) and with a 90 ft grounded tower in the center.

https://s26.postimg.org/oao5xh9zd/N2_WQ-1.png

As others have said, when all four elements are fed via the hybrid coupler controller the SWR will be relatively flat and is not a good indication of array performance.  Here's a comparison of the SWR curves for a single element fed directly (via the RigExpert analyzer) vs all four elements fed via the control box.

https://s26.postimg.org/v2el0byyx/N2_WQ-2.png

The fact that Rudy reported slightly different SWR values when the controller was switched to different directions is an indication that the elements are not perfectly identical, at least in an electrical sense, probably because of different coupling to other conductive structures in the vicinity, or slightly different heights above ground for the single "radial", or small differences in the ground characteristics under each element.

At Rudy's intended design frequency of 3.550 MHz here's what the azimuth, elevation, and 3D patterns look like.  Note that the forward gain is only ~3.9 dBi (should be closer to 5 or 5.5 dBi) and the F/B is only ~18 dB.

https://s26.postimg.org/kpsae95ft/N2_WQ-3.png

The pattern could be improved a bit but that is really not the main problem.  Instead, take a look at the frequency sweep curves for dumped power and azimuth pattern F/B.

https://s26.postimg.org/c68wghx3d/N2_WQ-4.png

The dumped power minimum is well below the design frequency and the F/B max (about 26 dB) is well above the design frequency.  Those two curves can be shifted by a) changing the (in isolation) resonant frequency of the elements and b) placing a shunt reactive component, capacitor or inductor, across port 2 and/or port 3 of the hybrid coupler in the DXE control box.

All of that is explained in the >5th< edition of the ON4UN book.  For those in Rudy's situation of trying to use an off-the-shelf control box with other than conventional quarter-wave vertical elements, you probably should consider getting the 5th edition.  That edition also has the details of how to include a hybrid coupler in the model.

Above modeling was done using AutoEZ:  http://ac6la.com/autoez.html

For a very detailed example of modeling this kind of 4-sq:  http://ac6la.com/aecollection8.html

Dan, AC6LA
http://ac6la.com