Hi Guys, Excellent point Tom as we will have to disagree on this. I have built both types of arrays here and like the smaller circle with active elements. I believe it has a "cleaner" pattern. You can see a 3D picture comparison of several arrays at "http://www.kkn.net/dayton2014/dayton-2014-antenna-forum.html" starting at page 11 There are some real differences between 8 element passive BSEF and the Hi-Z 8A npatterns. Receiving antennas are all about hearing what you want and getting rid of what you don't want. I think the 3D pictures show this pretty well. We almost never design RX antennas for gain, only how it receives which is mostly about pattern or directivity. The observations by Joel will indeed be interesting, These two antennas are VERY close in performance and I think the differences will be interesting, who knows, it may spur the development of something new. Go Joel! Lee K7TJR
-----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Tuesday, December 16, 2014 4:52 AM To: Lee K7TJR; 'Bob Tabke'; topband@contesting.com Subject: Re: Topband: 8 circle: DXE vs Hi-Z Lee, We probably will just have to disagree about this. >From my viewpoint, the behavior isn't too much different than a big yagi stack or other antennas we are used to. The size of the array generally sets the directivity limits. We can add more elements that are closer-in than optimum, and that can certainly help if the size is smaller than optimum, but the trade is gain or pattern cleanliness and sharpness for size. The forward two elements and back two elements are too close to contribute broadside pattern, which is what provides the clean pattern absent major side lobes in the full size 8 circle. As a matter of fact, adding them in destroys some of the broadside directivity. If, however, we make the array so small that it loses broadside pattern multiplication, then we can see an increase in directivity through the small endfire length increase. A .327wl radius array gives about .25 wl endfire spacing in the primary cells (the center elements), and is not improved in pattern quality by adding the forward and rearward cells. The two forward pairs and rearward pairs are not only too close to have broadside pattern contribution, they are closer endfire. They are about 75% of the endfire spacing in the central quad, and nearly 40% of the broadside width. They certainly can contribute endfire, but they actually remove broadside directivity in the process! In an optimum size array the amplitude ratio from the primary quad has to be 4:1 or 5:1 or more to prevent some pretty significant pattern null area deterioration when the additional 4 elements are added, because they deteriorate broadside pattern multiplication faster than they contribute endfire gain (at ~.187 spacing when the primary endfire cell has .25 wl spacing). If the array is made so small that there is little broadside contribution from array width, then the addition of the four will improve things. There isn't any broadside pattern to hurt. That isn't the same as a broad general statement that using more of the elements allows the array to be made smaller, unless we want to compromise pattern to have the same directivity. I go through similar things with Yagi arrays. All of my Hygain 5 element Yagis have been changed to four elements, and my KLM six elements have become 5's. :) It isn't so much they work better, they just work different in a way that is a better compromise for pattern, bandwidth, complexity, and gain. Everything is a compromise. If the target is maximum directivity and a clean pattern (more like a flashlight), the array has to be large. It can never be the same if small, or we all be running multi-element short boom antennas in close-spaced stacks. I do agree, however, if space is so limited the array can't use broadside multiplication (which is the same as stacking gain in a Yagi array) then all active elements with more elements is better. 73 Tom _________________ Topband Reflector Archives - http://www.contesting.com/_topband