Telecom tower inspection: checking towers and antennas without switching off the signal

Telecom structures include self-supporting lattice towers, steel monopoles, guyed masts and rooftop towers. Beyond rust and bolts on the structure, they carry a crowd of antennas, radios, cables and mounts — and equipment is added or replaced with each new network generation.

Telecom towers are traditionally inspected by specialist tower climbers. Binoculars from the ground cannot see behind antennas or into mounts. When working right next to antennas, transmitters may be switched off so climbers are not exposed to strong RF — which affects service in the area for that time.

The core pain is numbers and danger. A single major operator runs a very large number of sites. In the United States, tower work has drawn particular attention from the occupational safety authority (OSHA) for its fall fatalities, which it counted at 13 tower-related deaths in 2013. In Japan, mountain-top relay stations and island towers take a whole day just to reach. And with infrastructure sharing, tower owners and equipment owners are increasingly different companies.

Telecom towers were among the first places drone inspection spread. Towers are compact and regular, so a short flight can capture everything.

The biggest change is having the whole tower without climbing it. With a 3D model, engineers can measure antenna orientation, find free mounting positions and plan the next job at a desk. Climbers go up only to repair or install.

How radius, speed and heading relate when you orbit a tower at a fixed distance can be explored in an interactive lab for orbit radius and speed (Airffic Aerial).

Around a telecom tower you face radio energy, steel and wind. Towers stand on high, open ground for line of sight, so they catch the full wind.

• Strong EM fields: RF is strongest directly in front of antennas. Decide in advance what the aircraft does on link loss (return home or hover). Strong EM fields
• Magnetic disturbance: steel towers and monopoles throw compasses off. Take off away from the structure. Magnetic disturbance
• Height: at mountain relay sites, tower height adds to terrain height. Watch altitude limits and positions where you lose sight of the aircraft. Height
• Wind & turbulence: ridges and rooftops are windy, with eddies around the tower. Keep margin so a gust towards the antennas does not mean contact. Wind & turbulence
• Rooftops & towns: under a rooftop tower are streets and people. Choose routes where a fall would not hit third parties. Urban areas

Telecom tower data serves two purposes: structural health and equipment records. Rust and missing bolts go to maintenance; antenna positions, orientations and equipment lists go to load calculations and planning the next job.

In Japan, steel masts above a certain height are treated as structures (kōsakubutsu) under the Building Standards Act, subject to permit and structural requirements. Telecom equipment is covered by technical standards under the Telecommunications Business Act, and transmitting stations by the Radio Act. Human exposure is guided by Japan’s radio-radiation protection guidelines, which inform work near antennas. Tall towers may need aviation obstruction lights or daytime markings under the Civil Aeronautics Act.

For drones, flying close to a tower is usually a specified flight within 30 m of property, requiring permission or approval. Depending on the radio system used for video downlink, a radio licence or operator qualification may be required, so check how the aircraft communicates. In the US, TIA-222 is the structural standard for antenna-supporting structures, FCC rules cover RF exposure, and FAA guidance covers obstruction marking and lighting. Compare flight rules in world regulations.

• Bolt tension: a loosening bolt is invisible in photos. Checking and re-tightening is human work.
• Inside monopoles and below anchors: internal corrosion of monopoles and below-ground anchor corrosion cannot be seen from outside.
• Water inside connectors: often invisible from outside; electrical testing is needed.
• Radio performance itself: antenna orientation can be measured, but whether coverage is right needs separate RF measurement (drone-based RF measurement is also being tried).
• Installation and repair: work on antennas and radios still needs climbers.
• Rating and accountability: whether equipment can be added and the tower is strong enough is a structural engineer’s decision.

What follows is the editors’ projection. Every town telecom tower has an up-to-date 3D model. Plans for new antennas start on screen, checking loads and mounting positions, and once the work is done a drone flies the same route to confirm it matches the plan.

After a storm, drones visit mountain relay stations in turn, finding antenna drift and fallen parts. Climbers go up already knowing where to fix and which parts to bring. Work at the top has lost its dangerous hours of searching; only the short time spent fixing remains.