Sorry not to respond sooner, but have been tied up in revising a book MS.
I modeled a 2-element DE-Refl beam in FS. The gain was about 6.1 dBi, F-B
about 10.7 dB, and the Impedance about 52 Ohms. Tilting the reflector by
20 degrees decreased the gain to about 5.7 dBi and the F-B to about 8.2
dB, with no significant change in the feed impedance. The most major
change does not show up in the standard numbers. The parallel elements
showed an extremely good front-to-side ratio, but when out of alignment,
the front-to-side ratio degraded considerably--by at least 10 dB.
Based on this quick modeling, I strongly recommend a trip to the top to
straighten the reflector--as soon as safe and convenient, of course.
Hope these notes help. I have not systematically looked at how far out
of alignment one has to get to really notice a difference or at the
effects of ground reflections on the matter. But perhaps this much will
be an indicator to others as well that pretty good alignment is necessaru
to get the most out of a Yagi.
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || email@example.com
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