Topband: Modeling W8JI and Hi-Z 8 Circles

[Dan Maguire via Topband]

The recent thread on 8 circle arrays prompted me to create a few different AutoEZ models, mostly because I was curious about the relationship between array size, element phasing, and number of active elements (4 with W8JI, 8 with Hi-Z).

First thing I did was educate myself.  For "W8JI type" arrays:

http://w8ji.com/small_vertical_arrays.htm
http://n3ujj.com/manuals/8%20Circle%20Vertical%20Array%20for%20Low%20Band%20Receiving.pdf
http://www.dxengineering.com/parts/dxe-rca8b-sys-3p
http://static.dxengineering.com/global/images/instructions/dxe-rca8b-sys-3p-rev3.pdf
Low-Band DXing, 4th ed, ON4UN, Chapter 7, Sections 1-21 and 1-30

And for "Hi-Z type" arrays:

http://www.k7tjr.com/need.htm
http://www.kkn.net/dayton2014/HiZ_DAYTON_2014_7n2.pdf
http://www.hizantennas.com/HiZ8-160&80_users_guide.pdf
http://www.hizantennas.com/Hiz_8_160&80_manual.pdf
http://www.dxengineering.com/parts/hiz-8a-lv2-160-2

Then I created models where the array size (diameter) can be controlled via a single variable, along with another variable to control the phasing.  For example, here's the AutoEZ Variables sheet tab for a W8JI type array.  The Hi-Z is similar except that array size is specified in feet (or meters) rather than wavelengths.

http://ac6la.com/adhoc/8circle1.png

Since everything is controlled by variables you can run "variable sweeps" changing one or more parameters.  Here's the W8JI array with the spacing ("B") held constant while the phase delay ("P") is swept from 80 to 140 degrees.  For each test case AutoEZ will automatically calculate the RDF (last column).

http://ac6la.com/adhoc/8circle2.png

When the calculations finish you can step through the 2D patterns.  Here are the elevation and azimuth (at 20° TOA) patterns for 0.604 wl broadside spacing and 125 degree phasing, as shown by "B" and "P" in the lower right corner.

http://ac6la.com/adhoc/8circle3.png

You can run similar sweeps changing the array size while holding the phase delay constant, or hold both size and phase constant and do a frequency sweep, or use the "Generate Test Cases" button to create any combination.  For example, the setup below would vary broadside spacing "B" from 0.50 to 0.70 wavelengths; for each "B" the phase delay "P" would be varied from 115 to 135 degrees; all at a constant frequency of 1.85 MHz.  That would be 25 test cases.  You can run thousands if you like.

http://ac6la.com/adhoc/8circle4.png

You can also show 3D patterns.  Here's an example of a Hi-Z array, diameter 200 ft with ±106 degree phasing, along with the 2D elevation pattern.

http://ac6la.com/adhoc/8circle5.png

And here's how the RDF for a 200 ft Hi-Z array varies as the phase is swept from ±100 to ±112 degrees.

http://ac6la.com/adhoc/8circle6.png  

For both of the array types, I created one model using W8JI-style top hat loaded vertical elements (per the sample model on Tom's site) and a second model using simple aluminum tube elements (per the four-section, 23.25 ft, Hi-Z AL-24).  Here are the models.  Save to your computer then use the AutoEZ "Open Model File" button.

http://ac6la.com/adhoc/W8JI_8_Circle__TopHat.weq
http://ac6la.com/adhoc/W8JI_8_Circle__AL-24.weq
http://ac6la.com/adhoc/Hi-Z_8_Circle__TopHat.weq
http://ac6la.com/adhoc/Hi-Z_8_Circle__AL-24.weq

Please note that these models have not been reviewed or approved by the authors of the references cited above.  Any mistakes or misinterpretations are strictly mine.  And the models may or may not be an accurate representation of any given commercial package.

In all the models, a single variable ("X") controls the segmentation.  You can reduce that to speed up the calculations.  You can also run a sweep on "X" to do a convergence test for model accuracy.

For comparison with the 8 circle arrays, here's the W8WWV "Benchmark Beverage" model.  With this one you can "sweep" the length and/or other parameters.

http://ac6la.com/adhoc/W8WWV_Beverage.weq

Greg's Beverage page for reference.

http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/Beverage.htm

Calculated results for this Beverage are shown in section "Calculate 3D Data" here.

http://ac6la.com/aeuse3d.html

===============

AutoEZ is an antenna modeling program which uses Microsoft Excel in combination with EZNEC.

http://ac6la.com/autoez.html

Current AutoEZ users, see here for recent maintenance updates and instructions on how to get the latest release.

http://ac6la.com/aechanges.html

Dan, AC6LA