WEBVTT NOTE Antennas, Towers, and Power Lines 1 00:00:00.000 --> 00:00:08.793 The rule that matters most. Stay clear of overhead electrical lines. Every other item in this lesson is secondary to it. 2 00:00:08.793 --> 00:00:21.322 The minimum safe distance from a power line when installing an antenna is enough that if the antenna falls, no part of it can come closer than ten feet to the power wires. 3 00:00:21.322 --> 00:00:29.968 Not the distance while you are holding it upright, the distance if it comes down, in the direction it would come down. 4 00:00:29.968 --> 00:00:44.036 This is why you never attach an antenna to a utility pole: the antenna could contact high-voltage power lines, and a utility pole is a structure built to carry exactly what you must not touch. 5 00:00:44.036 --> 00:00:59.643 A vertical antenna and a length of wire are conductive, long, and awkward. The common accident is not dramatic; it is someone walking a mast upright, losing control of it, and having it fall across a service drop. 6 00:00:59.643 --> 00:01:15.526 Climbing. The pool asks under what circumstances it is safe to climb a tower without a helper or observer. The answer is never. Not "when it is short". Not "when you are experienced". Never. 7 00:01:15.526 --> 00:01:29.235 What is required when climbing: A carefully inspected climbing harness, and a helper or observer,. the harness clipped to the tower before releasing your grip, and. 8 00:01:29.235 --> 00:01:41.941 not climbing above the top guy attachment on a guyed tower. Crank-up towers must not be climbed unless they are retracted, or fully supported by blocks. 9 00:01:41.941 --> 00:01:48.378 The cable can fail; the sections can telescope down; both have killed people. 10 00:01:48.378 --> 00:01:55.750 Guy wires and turnbuckles. A safety wire through a turnbuckle prevents it loosening from vibration. 11 00:01:55.750 --> 00:02:07.366 Guy tension is set once; wind then works at it for years, and a turnbuckle that backs off slackens a guy and unbalances the whole system. Grounding a tower. 12 00:02:07.366 --> 00:02:22.780 Two facts, both counterintuitive: Separate eight-foot ground rods for each tower leg, all bonded together. Not one rod for the tower, one per leg, then bonded, and then bonded to the station's ground system. 13 00:02:22.780 --> 00:02:37.747 Surge current wants the shortest path to earth from wherever it lands. Avoid sharp bends in grounding conductors. A lightning surge is a very fast transient, and a sharp bend presents inductance to it. 14 00:02:37.747 --> 00:02:48.991 The surge will jump the bend rather than follow it, which puts the energy somewhere you did not choose. Keep runs short and direct, with gentle curves. 15 00:02:48.991 --> 00:03:00.458 Local electrical codes establish grounding requirements for a tower or antenna. Not the FCC, not the ARRL, the code where you live, and it is enforceable. 16 00:03:00.458 --> 00:03:13.555 A pre-installation checklist. Trace the path of the antenna if it falls, in every direction. Ten feet from any power line, in all of them. Never attach to a utility pole. 17 00:03:13.555 --> 00:03:30.041 Harness inspected; helper present; clip on before letting go. Crank-up retracted or blocked before anyone climbs. Safety wires through turnbuckles. Ground rod per leg, all bonded, short direct runs, no sharp bends. 18 00:03:30.041 --> 00:03:44.679 Check the local code before, not after. Check yourself. A 30-foot mast is going up 25 feet from a service drop. Acceptable? Your neighbour offers to spot you from the ground while you climb. 19 00:03:44.679 --> 00:03:54.155 Does that satisfy the requirement? Why does a sharp bend matter in a lightning ground conductor but not in a DC power lead? 20 00:04:00.155 --> 00:04:17.802 Only if, when it falls, no part reaches within ten feet of the lines. A 30-foot mast 25 feet away does not clear that, it can reach the line. Yes, a helper or observer is required and a competent one satisfies it. 21 00:04:17.802 --> 00:04:35.864 The harness, its inspection, and clipping on before releasing your grip are all still required. A lightning surge is a fast transient, so conductor inductance matters and a sharp bend is inductance the surge will jump. 22 00:04:35.864 --> 00:04:39.675 DC sees only resistance, and a bend adds none.