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Re: Topband: Modeling W8JI and Hi-Z 8 Circles

Subject: Re: Topband: Modeling W8JI and Hi-Z 8 Circles
From: Dan Maguire via Topband <>
Reply-to: Dan Maguire <>
Date: Tue, 23 Dec 2014 00:55:15 -0800
List-post: <">>
Based on some user feedback, the 8-circle models mentioned earlier have been 
modified with an additional variable to control the azimuth direction of the 
main lobe.  That lets you change the direction just by changing (or doing a 
sweep on) a single variable.  So you can easily:  1) see how the azimuth 
patterns overlap as the array is steered in 45° steps, and 2) compare patterns 
against other models which may be fixed in a particular direction.

For case 1, here's how the "Hi-Z type" (8 elements in use) 8-circle array 
patterns would overlap as you turn the knob on the control box.  This is for a 
200 ft diameter array with ±106° phasing, 20° TOA for the patterns.  Compass 
rose angles are shown in parenthesis.

For case 2, this is how a "W8JI type" (aka BroadSide/End-Fire or BSEF, 4 
elements in use) 8-circle array with 0.604 wl broadside spacing and 125° 
phasing compares against a 4-square receiving array with 0.125 wl element 
spacing and Crossfire feeding.  Both arrays use the same basic element, the top 
hat model rxvrhat.ez from Tom's page.  At a 20° TOA the 4-square has a gain of 
-22.43 dBi compared to -10.95 dBi for the 8-circle.  (But the RDF is only about 
1 dB lower for a diameter of 94 ft compared to 348 ft for the 8-circle.)  In 
order to get an accurate comparison of the pattern *shapes* on a common polar 
chart, the *gain* of the 4-square has been normalized to that of the 8-circle 
by reducing the value of the swamping resistors.  Original gain below on left, 
normalized gain below on right.

The 4-square can be fed either as Crossfire or BroadSide/End-Fire using exactly 
the same phasing lines, a neat idea picked up from IV3PRK.  In the patterns 
below, the swamping resistors are back at the normal values (to give 75+j0 at 
the feedpoint for a standalone element).  With Crossfire feeding the gain at 
20° TOA is down 7.45 dB compared to BSEF feeding but the RDF is 2.1 dB better, 
below left.  Note that a design criteria for IV3PRK was good rejection at 
backside 45°, below right.

For more details on this dual-feed 4-square see the "Receiving Antennas" 
portion of the IV3PRK site and follow the links on the left side of the page. 

Finally, thank you Jim Brown for mentioning the 2014 Contest University W3LPL 
"Receiving Antennas" presentation.  Lots of good info there.  Here's the direct 

These are the revised 8-square models with the additional variable to change 
the pattern direction.

And here's the 4-squareRX model with a variable that switches between Crossfire 
feed and BSEF feed.

Dan, AC6LA
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