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oh7ug Antenna

New "Shortened" 26 m Siderpole Fiberglass Vertical

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The nThe 26 m Spiderpole is shortened to 20+m by taking off three top sectionsew 26 m Spiderpole fiberglass antenna arrived late June. Due to holiday trips and other Summer activities I got it up on 7th August. I wanted to have a support for vertical and possible wire antennas. It should be easy to handle and set up, but be something more rigid than the earlier 18 m Spiderpole which broke during a storm earlier this Summer. A good, though more costly, solution was to deploy the new 26 m Spiderpole. I have taken off three topmost sections (whip), leaving total of 12 sections of the telescoping pole. Total height is somewhat above 20 m. Tip diameter is 30 mm and bottom about 110 mm.

2mm OD copper wire runs inside the poleThere are 30 radials (variying from 4 to 20 m in length) dug 2-3 cm into the ground, using bare 2,5 sq mm household wire (the insulation stripped off). Currently I have about 600 m of wire in the radial system. The house and nearby lot border restrict layout of the radials. They cover only about 2/3 of full circle in a bent hourglass shape.

2 mm OD enamelled copper wire runs inside the pole. I have pulleys at top and topmost guying point for easy installation of wire antennas. The top cover and pulley are assembled with a 30 mm rubber boat plug, some steel strap with heat shrink rubber and a clamp - all stainless steel.

Gyuing belts and top plug with pulley

The pole is guyed with three guy lines at three levels. The guy lines are 3 mm OD Dyneema racing boat rope breaking strength over 450 kg. 

Three guying belts came with the 26 m Spiderpole for easy guy line attaching. The belts are a good place to attach pulleys for wire antennas, too.

Guy wires and guying belt

Top plug and pulley attachment before assembly

Three guy wires are attached to belts at each level, 120 degrees apart. Try to get the topmost angle at least 30 degrees to ensure rigidity and lower the stress to pole. At 30 degrees the horizontal wind pressure gives 1,7 times more stress towards ground along the vertical pole and 2 times more along the guy line. This comes from simple trigonometry and Newtons laws. To overcome the stress along the pole I added a second clamp above each section below the bottom guying point.

Bottom sections have two clamps, both above the lower section to prevent telescoping in

The pole got it's wind test one day after setting it up, when Helsinki area was hit with a heavy thunderstorm, wind speeds reaching 30 m/s. The pole survived. It is remarkably more rigid and stable than the previous 18 m pole.

Last Updated on Saturday, 22 January 2011 20:03  

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