7.4 Lightning Protection and Station Security

ACMA Amateur Radio Standard Recognition Certificate - Theory Exam

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1 Chapter 1: Electrical Principles and Components

1.1 Mathematics, Units and Metric Prefixes 1.2 DC Circuits, Voltage, Current, and Ohm's Law 1.3 Power, Energy, and Resistance Calculations 1.4 Resistor Colour Code and Component Symbol Identification 1.5 Capacitors: Construction, Ratings and Safety 1.6 Inductors: Construction, Factors Affecting Inductance and Combinations 1.7 Capacitor and Inductor Combination Calculations 1.8 AC Circuits, Frequency, Wavelength, and RMS Values 1.9 Reactance and Impedance in AC Circuits 1.10 Resonance, Q Factor and Tuned Circuits 1.11 Transformers: Turns Ratio, Impedance Matching and Eddy Currents 1.12 Rectifiers, PIV and Power Supply Smoothing 1.13 Active Components: Semiconductors, Diodes, and Transistors 1.14 Transistor and FET Symbols, Configurations and External Behaviour

2 Chapter 2: Transmitters and Receivers

2.1 Superheterodyne Receiver Architecture and Block Diagrams 2.2 Frequency Converters, IF Amplifiers and Transceiver Sharing 2.3 Receiver Performance: Sensitivity, Selectivity, and AGC 2.4 Signal-to-Noise Ratio and Receiver Noise Performance 2.5 Transmitter Architecture, Oscillators and Frequency Synthesisers 2.6 Transmission Quality: Frequency Drift, Parasitic Oscillation and Over-Modulation 2.7 Modulation Techniques: AM, FM, and SSB 2.8 Amplifier Classes and Power Amplifiers (Class A, B, C, and AB) 2.9 Modulation, Duty Cycle and Rated Transmitter Power 2.10 Transceiver Control: ALC, Squelch, and Digital Modes 2.11 Digital Transmission Modes and Bandwidth

3 Chapter 3: Transmission Lines and Antennas

3.1 Transmission Lines: Coaxial, Twin-Lead, and Characteristic Impedance 3.2 Standing Wave Ratio (SWR) and Reflection Loss 3.3 Impedance Matching, Baluns, and Antenna Tuning Units (ATUs) 3.4 Resonant Antennas: Dipoles, Verticals, and End-Fed Antennas 3.5 Angle of Radiation, Antenna Height and Current Distribution 3.6 Directional Antennas: Yagis, Gain and Radiation Patterns 3.7 Effective Radiated Power: System Gains and Losses

4 Chapter 4: Radio Wave Propagation

4.1 Electromagnetic Waves: Velocity, Wavelength and Polarisation 4.2 Ground Wave, Direct Wave and Line-of-Sight Propagation 4.3 Ionospheric Layers (D, E, F1, F2) and Skywave Propagation 4.4 Critical Frequency, Maximum Usable Frequency (MUF), and Fading 4.5 Solar Activity, Sunspot Cycles, and VHF Anomalous Propagation 4.6 Seasonal and Diurnal Effects on Band Selection

5 Chapter 5: Electrical and RF Measurements

5.1 Multimeter Operation: Voltage, Current, and Resistance Measurements 5.2 RF Power and SWR Measurement (PEP vs. Average Power) 5.3 Frequency Counters, Dummy Loads, and Test Equipment 5.4 Frequency Standards, Crystal Calibrators and Standard-Frequency Transmissions

6 Chapter 6: Interference and Electromagnetic Compatibility (EMC)

6.1 Harmonic Emissions, Spurious Signals, and Transmitter Filtering 6.2 How Interference Enters Television and Broadcast Receivers 6.3 Masthead Amplifier Overload and Audio-Stage Demodulation 6.4 Electromagnetic Interference (EMI), Breakthrough, Ferrites, and EMC 6.5 Filter Types, Response Curves and EMC Filter Selection 6.6 EMC Good Practice: Minimum Power, Balanced Antennas and Feedline Routing 6.7 Vehicle EMC and Resolving Community Interference Complaints

7 Chapter 7: Safety and Environmental Hazards

7.1 Mains Voltage Safety, Earthing, and High-Voltage Capacitors 7.2 Equipment Approval, Mains Wiring and Fuse Practice 7.3 Station Layout, Cabling and Emergency Shut-Off 7.4 Lightning Protection and Station Security 7.5 Electric Shock: Prevention, Rescue and Emergency Response 7.6 Battery, Chemical and Hearing Safety in the Amateur Station 7.7 RF Exposure: EMR Hazards and Safe Distance 7.8 Antenna Erection, Siting and Power Line Safety

7.4 Lightning Protection and Station Security

Key Takeaways Explain This Topic AI

Syllabus 10.20: install lightning protection on antennas, disconnect antennas from the radio equipment before a thunderstorm, and never operate an amateur station during a thunderstorm.

Physical disconnection beats any arrestor — an air gap between the coax plug and the transceiver is a better insulator than any device you can buy, and a gas discharge tube arrestor only diverts induced surges.

All lightning and RF earth electrodes must be bonded back to the building's main earthing (MEN) system; separate unbonded earths reach very different potentials during a strike and flash over through the station.

Australian storm exposure is high — the northern wet season runs roughly November to April and the south-eastern storm season from about September to March — so disconnection is a routine habit, not an exception.

Syllabus 10.22: an operable amateur station must not be accessible to unauthorised persons — lock the room or cabinet, remove the microphone or key, isolate at the master switch, and password-protect any remote access.

Last updated: July 2026

7.4 Lightning Protection and Station Security

ACMA Exam Focus: Syllabus items 10.20 and 10.22 — recall that it is good practice to install lightning protection on antennas, to disconnect antennas from radio equipment before a thunderstorm and to never operate an amateur station during a thunderstorm ; and that an operable amateur station must not be accessible to unauthorised persons.

Part 1: Lightning (10.20)
Why Your Antenna Is a Target

An amateur antenna is usually the tallest, best-earthed metal object on the property, which is precisely the profile a lightning discharge is looking for. A direct strike delivers tens of thousands of amperes with a rise time measured in microseconds. Nothing in an amateur station survives that; the object of lightning protection is to keep the energy outside the building and to keep people alive.

Most damage, though, is not from direct strikes. It comes from induced surges — a strike hundreds of metres away couples into feedlines, rotator cables, mains wiring and telephone or data lines, and arrives at the back of the transceiver as a fast, high-voltage transient.

Australia gives you plenty of opportunity to find out. The northern wet season , roughly November to April, brings near-daily storms across the Top End and the tropical north, with Darwin recording more thunder-days than any other capital. The south-east has a spring and summer storm season from about September to March, and severe storms are common along the eastern seaboard. Treat lightning as a seasonal certainty, not a freak event.

Building Protection Into the Installation

Earth the mast or tower directly. Run a heavy conductor — copper strap or large cross-section cable — down the outside of the structure to one or more driven earth electrodes. Keep the run as short and straight as possible: lightning current will not negotiate tight bends, and a sharp bend invites the discharge to jump sideways to something else.

Bond the coax outer conductor where the feedline leaves the structure, and again at a single-point earth entry panel on the outside wall where all feedlines enter the building. Every feedline, the rotator cable and any control cable land on that one panel.

Fit gas discharge tube (GDT) coaxial arrestors on the entry panel. A GDT is a sealed spark gap: it is effectively invisible to normal RF voltages, but it ionises within nanoseconds when a surge reaches a few hundred volts and shunts the energy to the earth bar.

Bond everything to one earth. Any earth electrode installed for the mast or the RF earth must be bonded back to the building's main earthing system — the MEN (Multiple Earthed Neutral) connection at the switchboard — with a heavy conductor. Separate, unbonded electrodes sit at wildly different potentials during a strike, and the difference flashes over through your equipment and possibly through you. This is the single most misunderstood point in amateur earthing.

Protect the mains and data feeding the shack with surge protection as well; a surge that cannot get in via the coax will happily use the power lead.

The Australian standards to be aware of are AS/NZS 1768 for lightning protection and AS/NZS 3000 for wiring. Anything that connects to the MEN system or the switchboard is licensed electrical work.

Why Disconnection Beats Every Arrestor

An arrestor is designed to divert induced surges. It cannot absorb a direct strike, and even when it operates it clamps to some voltage well above zero. A physical air gap of a metre between a coax connector lying on the floor and the back of your transceiver is a better insulator than anything you can buy.

So the syllabus rule is disconnection, and it is done properly:

Unplug the feedlines, rotator cable and control cables from the equipment .

Put those connectors somewhere useful — into grounded bulkhead sockets on the entry panel, in a metal box, or outside the shack entirely — not coiled on the desk beside the radio, where a flashover will simply jump the gap.

Unplug the mains leads and any network cable too.

Do it when the forecast is issued or the storm is still distant , not when the thunder gets loud. Strikes can precede the rain by many kilometres.

Never Operate During a Thunderstorm

This is an absolute in the syllabus, and it is about the operator, not the equipment. Do not transmit, do not sit at the operating position listening, and do not stand near the feedline entry point. If you can hear thunder, you are close enough to be struck. Wait until the storm has clearly passed — the widely used rule is 30 minutes after the last thunder — before you reconnect anything. And never climb a mast, raise an antenna or handle a feedline with a storm anywhere in sight.

Situation Correct action
Storm forecast for this afternoon Disconnect feedlines and mains before you leave the shack
Distant thunder while operating End the contact, shut down, disconnect and leave the equipment alone
Storm overhead Do not operate and do not touch equipment, feedlines or the earth system
30 minutes after the last thunder Reconnect and resume
Leaving the station for days or a season Disconnect at the entry panel as standard practice
Part 2: Station Security (10.22)

An operable amateur station must not be accessible to unauthorised persons. The syllabus states it plainly, and the reasons split neatly into compliance and safety.

Compliance. A callsign is personal to the qualified amateur. An unqualified person may only operate under the direct supervision of a qualified amateur; unsupervised, they are transmitting unlawfully and doing so under your callsign. Anything they say, any band they wander onto and any interference they cause comes back to you as the person responsible for the station. The consequences run from an embarrassing complaint to interference with emergency or aeronautical services.

Safety. An amateur station left powered up and connected is a hazard to the untrained. A linear amplifier holds lethal charge in its capacitors even after it is switched off; heatsinks and valve envelopes are hot; open-wire feeders and low antennas produce RF burns; and a child who keys a transmitter has no idea which of those things is dangerous.

Risk Practical control

Children or visitors keying the transmitter Lock the shack room, or keep the equipment in a lockable cabinet; never leave a live station unattended

Casual unauthorised operation Remove the microphone, key or paddle and store it separately from the radio

Determined access to a powered station Switch off and lock the master isolator, pull a fuse, or remove the DC connector from the power supply

Contact with stored high voltage inside equipment Keep covers fitted and the cabinet locked; only qualified persons work inside an amplifier

Antenna left connected while you are away Disconnect at the entry panel — this satisfies security and lightning protection in one action

Remote or internet-controlled stations Strong unique passwords, no default credentials, restricted or VPN access, a transmit watchdog timeout, and remote control disabled when the station is unattended

Theft or misuse of the callsign Physical security of the room, recorded serial numbers, licence and log details kept secure

The habit that satisfies almost all of this takes about fifteen seconds on the way out: master switch off, microphone away, antenna disconnected at the entry panel, door locked. It closes the security requirement of 10.22 and most of the lightning and fire risk at the same time.