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[TowerTalk] 80m full size yagi

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Subject: [TowerTalk] 80m full size yagi
From: Don Moman <> (Don Moman)
Date: Thu, 4 Jun 1998 16:27:36 -0600 (MDT)
One of this summer's projects is to build a 3 ele 80m yagi.  Actually it
is coming along fairly well, with the boom constructed and currently
working on the driven element (split, insulated) mounting, nearly done

There will be 85' of boom (aluminum) to work with, altho some of that will
go towards mechanical advantage for the truss supports.  The boom will
consist of a 5' center section, which will support the truss and winch
mechanism to tilt up the two 40' boom halves. This will allow the dir and
ref to be mounted (each in their own integral 10' section of boom c/w
trussing etc) as the boom lays vertically against the tower.

The elements will be somewhat along the lines of the I5NPH design
presented in ON4UN's Low Band DXing (1st edition), converted to locally
available sizes.

The end result will be installed at 160 feet (40' face guyed structure) 
although that may not be this year. From about 340 to 90 degrees the
terrain slopes several hundred feet after the first 2500 feet (approx) 
from the tower.  It's reasonably level (gently rolling) in the other
directions. I have a 120' self supporting "test"  tower which may be the
temporay home over the winter until the mechanical design is proven (or
not). Time and the length of our summer will be factors, of course.

I'm still quite some time away from having to determine final length of
the elements, but I do need to firm up the spacing fairly soon. Electrical
lengths for the two yagi designs are given in John's book, but spacing
isn't really mentioned. I was planning to use the W2PV simplistic design
mentioned on page II-110, with .15 wave equal spacing.  I've noticed both
designs presented vary from the lengths in the W2PV design - especially
the reflector length. Comments?  There isn't too much one can do with a 3
element design, but I'd be interested in other sources of info detailing
construction of such a yagi. Internet searches haven't proved useful so
far, but that may just mean I'm looking in the wrong places. I'm also
curious to know how many of these yagis are still up and performing?  

I've heard of several others that have suffered early failures. The
Alberta climate at this QTH, near Edmonton) is usually quite benign to
larger antennas, with minimal icing and (not concurrently) winds rarely
exceeding 100km/h. Max peak gust here in the last 5 years was 90 km/h. 
Thanks, 73
Don  VE6JY

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