|
One of the primary features of this antenna is the ability to be erected (or lowered) with one person. Basic physics indicates the level of task required to lift a pole that weights around 30 pounds, and is 60 feet long. The pivot assembly went through many iterations before settling on this design. A goal was to provide some degree of mechanical advantage, because if you try to raise a pole that has a center of gravity around 35 feet above the pivot point from only 5 feet above the pivot point requires almost 200 pounds of torque (rotational lift). By installing a pulley system with a 5 to 1 mechanical advantage, this ideally is reduced to 40 pounds of force. With the addition of frictional losses, it is still an effort to raise, but clearly do-able by 1 person. |
The pulley system is made using a pair of dual pulleys, and 3/16 inch dacron. Using an eye bolt screwed into the top of the 4 x 4, and a 2 inch chain link to secure one pulley (pulley 1) to the eye bolt, the dacron rope is tied using a clove hitch to the 2 inch Aluminum mast at the very top of the 2 inch PVC. The rope then goes around the Aluminum securing the other pulley (pulley 2) with 2 loops and then a half hitch secures the knot. The rope is then dressed through pulley 1, then back to pulley 2, back to the other side of pulley 1, and back through the other side of pulley 2, and then finally back through the eye bolt. This section of dacron rope will be about 30 feet long. The end of the rope is tied in a figure-8 knot to secure the end from fraying. A cleat is mounted on the back side of the 4 x 4 about 3 feet from the top of this pole. This cleat is used to secure the rope once the antenna is pulled up. |
The pulley shown, with the free end tied back to the PVC sleeve.
| A close up of the pulley, when the vertical is in its up-right position. There is no tension on the rope, because the hinge 2 x 4 is secured to the 4 x 4 base pole using the steel bar secured with lag bolts. |
| The vertical being raised (at 40 degrees). I raised this, secured the dacron line, and stepped back to take the picture. Even the aluminum shows some flex. While raising, the person pushes on the PVC pole a few inches at a time, and then takes up the slack on the pulley. THE PULLEY IS NOT THE PRIMARY LIFTING TOOL - You are . |
The vertical is now up at a 75 degree angle. Note that the aluminum is hardly flexed, but the fiberglass section (with the loading coil weight) is really flexed. This fiberglass acts like a spring, and will really whip up and down. Time the lifting force until the pole is whipping up, helping reduce the actual force required to get it vertical. Once the pole is vertical, secure the position using the lag bolts into the holes which have been pre-drilled to align with the steel plates. Then coil up all the dacron neatly and secure using the marine cleat. |
| The pole is now vertical, secured in place. This antenna has survived winds around 50 MPH. The poles whip quite a bit, but they always seem to return to vertical once the wind dies. I did not notice any variation in received signal strength while they were whipping during the first night of CQWW DX Phone, when were were dumped with a severe thunderstorm. |