7.8 Antenna Erection, Siting and Power Line Safety

7.8 Antenna Erection, Siting and Power Line Safety

ACMA Exam Focus: Syllabus items 10.18 and 10.19 — recall that antenna erection is potentially dangerous and should be carried out by suitably qualified persons, and that antennas and their fittings must be suitably located and secured and must never be connected to, or sited close to, mains poles and lines.

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The Most Dangerous Thing Amateurs Do (10.18)

The serious injuries and deaths recorded in amateur radio are almost never caused by the transmitter. They happen outside, during antenna work, because three hazards arrive at once: working at height, heavy and unstable loads, and energised conductors overhead. Add an enthusiastic helper, a hot Saturday afternoon and a mast that is a metre longer than everyone remembered, and the margin disappears.

That is why the syllabus says the work should be carried out by suitably qualified persons. In practice that means matching the person to the job:

If the honest answer is that nobody present is qualified for the job, the correct decision is to stop and pay somebody who is. A tower is cheaper to install twice than to fall off once.

Never Connect To or Site Near Mains Poles and Lines (10.19)

The rule has two halves and both are examinable.

Never connect anything to a mains pole or line. Using a distribution pole, a streetlight column, a stay wire or a service bracket as a convenient support for a dipole end, a halyard or a guy is prohibited everywhere in Australia. It is trespass on network assets, it can bridge insulation, and it puts you within touching distance of conductors while you rig it. The same applies to throwing a wire antenna over anything near a line, and to using the mains earth or a water pipe as an antenna counterpoise.

Never site a structure where it could reach a line. Australian suburban blocks commonly carry 230/400 V low-voltage mains along the rear boundary, often with 11 kV or 22 kV high-voltage conductors on the same poles above them. The low-voltage line will kill you just as effectively as the high-voltage one; the high-voltage one does not even require contact, because it can flash over an air gap to an approaching conductor.

The Falling Rule

The safe siting test is simple: if the whole structure falls, no part of it may reach a conductor. So the horizontal distance from the base to the nearest overhead line must be greater than the total height of everything you are erecting — mast, plus antenna on top, plus any section you might extend later — plus a safety margin of at least 3 metres.

The margin is not decoration. A toppling mast sweeps an arc slightly longer than its own height, guy wires whip well beyond the tip, a wire antenna can be blown sideways as it comes down, conductors sag further on a hot day and sway in wind, and the person raising the mast can stumble a step in the wrong direction.

On top of this, every state and territory electrical safety regulator publishes legally enforceable exclusion zones — often called no go zones — around overhead lines for people who are not authorised electrical workers. A commonly published figure is 3 metres for lines up to 132 kV, with substantially larger distances at transmission voltages, but the numbers and the paperwork differ by jurisdiction. Check the rules for your own state before any work near lines, and remember that they apply to ladders, poles, tools and squid poles as well as to your body.

Securing the Structure: Masts, Guys and Anchors

• Footings. A self-supporting or guyed tower needs a designed concrete footing; a light mast needs a base plate through-bolted into structure, not screwed into a batten or a rotten fascia.
• Guy geometry. Use three guys at 120 degrees or four at 90 degrees, evenly tensioned. The anchor radius should ideally be around 80% of the height to the guy attachment point and never less than about half of it — a shallow guy angle multiplies the downward compression on the mast enormously.
• Anchors. Use proper screw-in or concreted anchors sized for the load. A fence post, a tree, a garden stake, a neighbour's carport or — worst of all — a power pole are not anchors.
• Strain insulators. Break metallic guys into non-resonant lengths with egg or strain insulators so they cannot act as parasitic elements or develop RF voltages at head height.
• Hardware. Use galvanised or stainless fittings, lock or mouse the turnbuckles, and inspect annually. Australian coastal salt air destroys plated steel in a season or two.
• Tilt-over and hinged masts are the amateur's friend: all antenna work happens at ground level. The dangerous moment is raising and lowering, when the load is least stable. Use a winch with a working brake — never a rope held by hand — keep everyone out of the fall arc, and never stand under a partly raised section.
• Crank-up masts must never be climbed unless fully retracted and pinned; the cables are a maintenance item with a finite life.

Handling, Ladders and Weather

1. Never erect an antenna alone. Two people minimum: one on the load, one watching clearances and able to call for help.
2. Brief the team first — who is in charge, what word stops everything, where the fall zone is and who stands where.
3. Carry masts, squid poles, ladders and vertical antennas horizontally, low, with a person at each end. Walking with an 8 m pole upright is how amateurs meet the service drop over their own driveway.
4. Ladders: use fibreglass or timber near electrical work, never aluminium; set the base out 1 metre for every 4 metres of height; foot or tie the ladder; extend about 1 metre past the landing point; and move it rather than overreaching.
5. Wear the gear: hard hats for everyone on the ground, gloves, eye protection and enclosed boots. On a tower, a full-body harness with two lanyards so you are attached at all times.
6. Stop for weather. Do not erect in wind, rain or with a storm approaching, and start early in summer to avoid heat stress on an Australian roof.

Wind Loading, Councils and Neighbours

Wind, not weight, sizes an antenna structure. Australian wind actions are set out in AS/NZS 1170.2, and the design wind speed varies dramatically by region — the cyclonic regions of northern Australia demand far stronger structures than an inland suburb. Manufacturers publish a wind-load rating as an antenna area at a stated wind speed; the antenna's projected area must fit inside the mast's rating for your region.

Before you build, check local council planning and building requirements (height triggers, heritage and overlay areas), your strata by-laws or tenancy agreement, and your insurer. Roof penetrations must be sealed and flashed properly and fixed into rafters, not battens. Getting written consent is cheaper than removing a tower.

If an Antenna Contacts a Power Line

1. Touch nothing and nobody. Do not touch the antenna, mast, guy, feedline, ladder, vehicle — or any person who is in contact with them.
2. Get everyone back. Stay at least 8 metres from a fallen or contacted conductor. Move away with small shuffling steps, feet together, because the ground itself carries a voltage gradient.
3. Assume everything is live, including the coax that runs inside to the shack.
4. Call 000 for ambulance, fire and police if anyone is injured, and call your electricity distributor's 24-hour faults and emergencies number — it is printed on your electricity bill — to have the line isolated.
5. Do not attempt a rescue with a 'dry stick'. That advice belongs to folklore; 230 V is lethal and high-voltage lines flash over.
6. If someone is in a vehicle touching a line, they should stay inside until the distributor confirms it is safe, unless there is fire.
7. Do not re-erect anything until the distributor has attended and the structure has been inspected.