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Re: [TowerTalk] Spring antenna project; replace vertical dipole

Subject: Re: [TowerTalk] Spring antenna project; replace vertical dipole
From: Jim Brown <>
Date: Tue, 29 Mar 2011 10:43:58 -0700
List-post: <">>
On 3/27/2011 7:31 PM, Rip R wrote:
> The tower approach is questionable; the HOA does not preclude antennas 
> per se
> since my verical dipole has been up for several years. I think that a 
> small tower
> will not be an issue.

If you're subject to HOA issues, I would try to stay as "low profile" as 
possible. Better to have something less than ideal than nothing at all. :)

You didn't say what bands you need to cover, how many wires you could 
put up, or at what azimuths.  The horizontal pattern of  a half-wave 
dipole is pretty broad -- about the only thing that really matters is 
where the NULLS are. In MT, the best directions for the nulls are at 0 
and 180 degrees (that is, run the antenna from N to S), and the worst 
directions for nulls are between 20 and 140 degrees, and between 200 and 
320 degrees.

As to height -- in general, it's worth trying to get a horizontal 
antenna up at least a quarter wavelength, so if 80 and 40 are important 
to you, give a higher priority to getting the antenna(s) for those bands 
up as high as possible. That doesn't mean that a lower antenna won't 
work, but rather that it will work better if it's higher.

As you know, I'm a big fan of fan dipoles, but it can be tricky to make 
them "low profile. To do that, think in terms of smaller wire diameter 
and small diameter spreaders. I use #10 for the longest element of very 
long wires that are very high in trees fed with RG8. It's also fine to 
use smaller diameter wire for the shorter elements that aren't part of 
the support line. #14 would work for lower wires between trees (or with 
a tree on one end) fed with RG8X, and you could get away with #18 for a 
wire between fixed supports.  If you're using a tree on either end, a 
pulley and weight are critical so that it doesn't break as the tree 
sways in the wind.

Smaller diameter wire can also work for inverted Vs that are supported 
from the center, because there's far less stress on them. If visibility 
was an issue, I'd go with #18 for all  elements.  You can also reduce 
visibility by using bare copper or enameled copper. You should use 
insulated wire if it will contact trees. .

One possibility for low visibility spreaders would be plastic dowel 
material that you cut into short pieces and drill holes through for the 
wire to pass through.  I use 1/2-inch PVC conduit because it's cheap, 
and visibility doesn't matter to me.

As to the support ropes -- the small diameter rope sold by Ham Radio 
Outlet and others is as strong (or stronger than) the copper, but it 
will fray and break if it rubs over anything but a decent pulley.

73, Jim K9YC

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