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The Antennacraft HBU and Winegard 769x line of antennas have the common characteristics of "delta wings" on two of the elements. The AntennaCraft literature states that these create additional UHF directors.

What's the theory behind this design? And what are the multiplex directors referenced in the notes for the HBU44 and HBU55?
 

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The "delta wings" appear to be capacitance hats. Per Ken Nist's glossary at http://www.hdtvprimer.com/ANTENNAS/GlossaryA.html

Capacitance hat - This is a device sometimes found at the end of an element. It can be a cross, a disk, a ball, a loop, or just about anything conductive. It makes the element behave as if it is longer, maybe 10%-30% longer than it really is. It can save space with almost no drop in performance. Capacitive hats are uncommon in TV antennas. (The Channel Master 3671B has six capacitive hats.)

what are the multiplex directors
Hmm, never heard of such a thing. Maybe someone can explain it.
 

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My CM1221 had a double director. By that I mean one director had a short aluminum uhf section in the middle, then fiberglass spacers on the ends, then longer vhf director aluminum sections on the same rod. Worked fine, and its what they had to do when the uhf and vhf director spacing fell in the same spot.
 
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