Wire Yagi Experts?
We at Marina Ca, (N6IJ Club Station) have a large converted
MARS radio station site which provides a opportunity to build a large
wire yagi array, possibly on 2 bands, (40 meters, 7 elements, 20
meters, 10 to 15 elements) pointed to Europe. There exist 4
wooden poles, 65 feet high, forming a rectangle 72 feet wide, by
350 feet long. If we guy them, and connect the poles with a
structural member (probably 5/16" ehs strand) from the power
company which is already available, we are contemplating
supporting the 2 large yagi arrays. A number of questions need to
be answered before proceeding..... and we are looking for some
outside input.
1. Will a grounded steel strand, structural member in the vicinity
of, but separated by approximately 20 feet from the tips of the
wire yagi (20 meter) elements, adversely affect the
performance of the yagi? By how much? (In the case of 40
meters the distance between the tips of the 40 meter yagi, and
the continuous strand will closer, about 5-10 feet.
2. Can we place a 20 meter yagi (possibly 8 to 12 elements) in
front of, and collinear with the "boom" of the 40 meter yagi
with relatively small separation without adversely affecting
either's performance?
3. The poles' long axis points to Europe (N 30 deg E), but they are
on a slight vertical incline, about 5 degrees uphill slope to
Europe. (Southwesterly ground elevation is 150 ft. MSL, and
Northeasterly ground end is 180 ft. MSL, in 350 foot span, a
30 foot rise in a 350 foot run. The yagi arrays, would be more
or less parallel to the ground below them, making a "boom"
angle of 5 degrees, to the horizontal. At the director
(Northerly) end, there is a flat plateau hilltop that the whole
antenna would illuminate, even the lower (reflector) end. The
arrays would be about 55 to 60 ft above ground. Would the
up-tilt of the boom add terribly to the vertical angle of radiation
of the array, compaed to a flat, level, yagi array?
4. Are there bandwidth problems with wire yagis, being that the
wire diameter is quite smaller than more typical, aluminum
tubing elements? We will use #10 Copperweld. Any way to
have an acceptable match on both phone and CW ends of 20
and 40 meters?
5. I have a detailed land countour map, with pole locations, that
could be used for a terrain-yagi model. Anyone interested in
modelling this?
6. If/when we complete this monster, we would like to invite
contesters/DXers to visit and use the station, already equipped
with KW rigs, 6-30mHz Log Periodics, and a Discone (80 - 10
meters). Contact me if you want to come down to operate, or
help construct these yagis....
7. Is it manageable/sensible to create such a large wire yagi
array?
What are the problems? If you have EXPERIENCE in WIRE
yagis, please advise. The poles are sturdy, in good shape,
class 2, 70 foot poles, buried in the solid sandy ground about
9 feet, and will be guyed. We may need a stuctural engineer
to alalyze the forces involved in this wire yagi array.
73, DX, de Pat, aa6eg@tmx.com
AA6EG; Trustee for N6IJ.
Marina CA.
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