[TowerTalk] Antenna recommendation for a low power east coast

[Jim Brown]

On 7/17/2013 1:03 PM, Eric Cary wrote:
> My other option is to use the trees for possible vertical arrays.

My 80 and 40 antennas are wires in trees, but the trees are redwoods, 
and the wires are at 110 ft, so they really play. :)  One is a 2-el wire 
Yagi for 40M.

A dipole at 35-40 ft is pretty good for 40 (although 65 is better), but 
just OK on 80.

IF, but ONLY if, you can put down a lot of radials, a 2-el or 4-square 
for 80 are worth considering. You might build build the verticals as 
top-loaded Tees, supported between trees.  If you haven't already done 
so, model some of these things in NEC, saving the vertical patterns so 
that you can overlay different antennas on the same graph. If you're 
going to do a 2-el array, I would use the Christman phasing network that 
is described in the ON4UN book.

There's another slick mechanical design that might work for you. We 
built 40M version for Field Day and CQP county expeditions, where we 
can't get dipoles up very high. It uses enough of the very nice military 
surplus 4-ft mating tubes to resonate, supported by a tripod base made 
of a tripod fitting and six more tubes. Once the radials have been cut 
to length with lugs on one end to facilitate connections, two people can 
built the array and lay out the radials in a few hours. My modeling 
predicts that it beats a low dipole at low angles by about 3dB, and it 
seems to work that way on FD. Also, be sure to study N6LF's extensive 
work on radials, especially his latest 2-part piece for QEX a year or so 
ago. All of his stuff is on his website.

Some guidelines about using the trees.

1) If the tree is used as a support for anything horizontal, a pulley 
and weight system is an absolute must.

2) You can support a dipole higher in a tree by using it as a center 
support for an inverted Vee than to support a horizontal wire (because 
there only downward forces on the tree), and the vertical pattern of the 
antenna will be largely determined by the height of the center. My 40M 
wire Yagi is rigged that way.

3) The higher you are rigged in the tree, the more it will sway, and the 
more likely something will break (including the tree).  My pulleys are 
up around 120-130 ft, which is 40-50 ft below from the tops of my trees, 
but they are supporting horizontal antennas fed with RG11. I'm using 
100# weights, made by filling 11 gal water jugs with dry sand.  Lots of 
ways to skin that cat. Some guys use window weights, buckets of 
concrete, etc.

73, Jim K9YC