Section 3: Station Assembly, Practice & Safety Canadian Amateur Radio Basic Qualification — Questions B-003-001 through B-003-021

3.1 HF Station Components B-003-001

An HF station is built from a chain of components that each play a specific role in getting your signal cleanly from the transceiver to the antenna. Understanding the order and purpose of each component is essential for both the exam and practical station building.

flowchart LR
  TX["TRANSCEIVER
(or TX + ext. amp)"] --> LPF["LOW-PASS
FILTER"]
  LPF --> SWR["SWR
METER"] --> TUNER["ANTENNA
TUNER"] --> SW["ANTENNA
SWITCH"]
  SW --> ANT["ANTENNA"]
  SW --> DUMMY["DUMMY
LOAD"]

Typical HF station signal path from transceiver to antenna

Low-Pass Filter Placement

A low-pass filter removes harmonics — unwanted multiples of your operating frequency — before they reach the antenna. Its placement depends on whether you use an external amplifier:

• Without external amplifier: Place the low-pass filter as close as possible to the transceiver output.
• With external amplifier: Place it as close as possible to the external amplifier output — always after the last stage of amplification, so its harmonics are also filtered.
• Built-in filters: Modern HF transmitters include built-in low-pass filters specifically to reduce harmonic emissions.

SWR Meter

The SWR (Standing Wave Ratio) meter measures how well your antenna system impedance matches the transmitter. A perfect match reads 1:1. It is the component you use to determine if the antenna system impedance is matched to the transmitter, and it is inserted in the signal chain right after the low-pass filter.

Antenna Switch, Tuner, and Dummy Load

The antenna switch lets you select the desired antenna or dummy load without disconnecting cables — a convenience that also prevents wear on connectors.

An antenna tuner matches impedance between the transmission line and the transceiver, which can allow you to use an antenna on a band it was not originally designed for. When using a transmitter with a solid-state final amplifier, the antenna tuner may need to be adjusted each time you change frequency, because solid-state devices are more sensitive to impedance mismatch than tube amplifiers.

A dummy load is designed to dissipate RF energy and prevent radiation. It converts RF power to heat, letting you test and tune your transmitter without broadcasting a signal on the air.

3.2 FM Transmitter Operation B-003-002

The FM transmitter differs from AM and CW transmitters in one fundamental way: the modulator varies the frequency of the oscillator rather than its amplitude. Understanding the signal flow through its five main stages is the key to answering every B-003-002 question.

flowchart LR
  MIC["MICROPHONE"] --> SA["SPEECH
AMPLIFIER"] --> MOD["MODULATOR"]
  MOD --> FM["FREQUENCY
MULTIPLIER"] --> PA["POWER
AMPLIFIER"] --> ANT["ANTENNA"]
  OSC["OSCILLATOR
(VCO)"] --> MOD

FM transmitter: modulator varies oscillator frequency. Key difference from AM/CW/SSB: the modulator changes the FREQUENCY of the oscillator, not its amplitude.

The microphone converts sound pressure waves into a small electrical signal. In an FM transmitter, this signal drives the speech amplifier, which boosts it to a level sufficient for the modulator. The FM microphone works the same as any other microphone — it produces an electrical signal from air pressure changes.

The modulator takes the amplified audio and uses it to affect the frequency of the oscillator. This is the defining characteristic of FM: unlike AM/CW/SSB transmitters where the oscillator runs at a fixed frequency, the FM oscillator's frequency shifts up and down in step with the audio signal.

The frequency multiplier takes the oscillator's output and multiplies it up to produce the FM output carrier frequency. In doing so, it produces a useful harmonic — an intentional multiple of the oscillator frequency. This allows the oscillator to run at a conveniently low frequency where it is easier to modulate accurately.

The power amplifier is the final stage, boosting the signal to the desired transmit power. It draws the most electric power of any stage in the FM transmitter.

3.3 Superheterodyne Receiver B-003-003

The superheterodyne ("superhet") design is used in virtually every modern receiver. Its genius is converting any incoming frequency to a single fixed Intermediate Frequency (IF), where one high-quality filter and amplifier chain can process every signal identically.

flowchart LR
  ANT["ANTENNA"] --> RF["RF AMP
(front-end)"] --> MIX["MIXER"]
  MIX --> IFF["IF
FILTER"] --> IFA["IF
AMP"] --> DET["DETECTOR"] --> AFA["AF
AMP"] --> SPK["SPEAKER"]
  LO["LOCAL
OSCILLATOR"] --> MIX

Basic superheterodyne receiver. FM adds: LIMITER (before detector) + DISCRIMINATOR (as detector). SQUELCH and VOLUME control are in the AF AMP stage.

Stage-by-Stage Functions

Each stage in the superhet chain has a specific job. The RF amplifier is the front-end stage that amplifies weak signals from the antenna. In a VHF receiver, this stage must be designed to produce very little noise, since any noise it adds will be amplified by all subsequent stages.

The mixer combines the incoming RF signal with the local oscillator (LO) signal. The result is a signal at the Intermediate Frequency (IF), which equals the difference between the two. The mixer is the stage that allows detection to function at a single fixed frequency regardless of what station you tune in — this is the key advantage of the superhet design. The local oscillator is what sets the received frequency: when you turn the tuning dial, you are changing the LO.

The IF filter provides the receiver's selectivity, rejecting signals on adjacent channels. The IF amplifier provides the final signal power needed to drive the detector stage.

For FM receivers, two additional stages appear. The limiter removes amplitude variations from the received signal (since FM carries information only in frequency changes, amplitude variations are just noise). The discriminator then recovers the original modulation from the FM carrier.

The AF (Audio Frequency) amplifier drives the speaker. It is controlled by the volume control and, in FM receivers, includes the squelch circuit that mutes noise when no signal is present.

3.4 CW Transmitter Operation B-003-004

The CW (Continuous Wave) transmitter is the simplest type of radio transmitter. It generates a carrier signal that is switched on and off by a telegraph key to form the dots and dashes of Morse code. A basic CW transmitter has just three stages.

flowchart LR
  OSC["OSCILLATOR"] --> BUF["DRIVER /
BUFFER"] --> PA["POWER
AMPLIFIER"] --> ANT["ANTENNA"]
  KEY["KEY"] -.->|"switches on/off"| OSC

CW transmitter: simplest type. The KEY switches the oscillator on and off.

The oscillator generates a signal at the transmitted signal's frequency. Each stage in the CW transmitter is powered by direct current (DC).

The driver/buffer stage sits between the oscillator and the power amplifier. Its critical purpose is to prevent load changes from shifting the oscillator's frequency. Without this buffer, changes in the power amplifier or keying action would "pull" the oscillator off frequency, causing an unstable signal.

In a basic three-stage CW transmitter, the key switches the oscillator on and off. More generally, the key switches the carrier on and off to form the dots and dashes of Morse code. The power amplifier stage increases the transmitter's output power to the desired level.

3.5 SSB/CW Receiver Stages B-003-005

An SSB/CW receiver is built on the superheterodyne design but adds two critical components not found in AM or FM receivers: a product detector and a Beat Frequency Oscillator (BFO). These are needed because SSB signals have their carrier removed at the transmitter, so the receiver must re-create it.

flowchart LR
  ANT["ANTENNA"] --> RF["RF
AMP"] --> MIX["MIXER"]
  MIX --> IFF["IF
FILTER"] --> IFA["IF
AMP"] --> PD["PRODUCT
DETECTOR"] --> AFA["AF
AMP"] --> SPK["SPEAKER"]
  LO["LOCAL
OSCILLATOR"] --> MIX
  BFO["BFO
(Beat Freq Osc)"] --> PD

SSB/CW receiver — note the product detector and BFO (not present in AM/FM receivers). AF AMP stage could include an audio band-pass filter.

The antenna converts electromagnetic waves into electrical currents. The RF amplifier increases the sensitivity of the receiver by boosting weak signals. The mixer converts the received signal into the intermediate frequency by combining it with the local oscillator output.

The local oscillator signal is mixed with the incoming signal to produce the intermediate frequency. The IF filter provides most of the selectivity of the receiver, while the IF amplifier provides most of the receiver gain.

The product detector is the key SSB/CW component — it recovers the transmitted modulation by combining the IF signal with the BFO. The BFO (Beat Frequency Oscillator) is mixed with the IF to recover the transmitted modulation. For CW reception, the BFO produces the audible tone you hear for each dit and dah.

The AF amplifier increases the level of the recovered modulation to drive the speaker. It could also include an audio band-pass filter for additional selectivity.

3.6 SSB Transmitter B-003-006

Building a Single Sideband (SSB) signal requires a multi-step process: generate a carrier, suppress it, remove one sideband, then shift the result to the operating frequency. Each stage in the SSB transmitter has a precise role in this signal-crafting process.

flowchart LR
  MIC["MICROPHONE"] --> SA["SPEECH
AMP"] --> BM["BALANCED
MODULATOR"]
  FO["FIXED RF
OSCILLATOR"] --> BM
  BM --> SF["SIDEBAND
FILTER"] --> MIX["MIXER"] --> FA["FINAL
AMPLIFIER"] --> ANT["ANTENNA"]
  VFO["VFO
(Variable Freq Osc)"] --> MIX

SSB transmitter: generates a single sideband signal and transposes it to the operating frequency

The fixed RF oscillator produces a stable RF carrier at a fixed frequency. The speech amplifier is needed because microphones have a low power output and the audio must be boosted to a usable level. Its job is simply to amplify the audio you wish to transmit.

The balanced modulator is where SSB creation begins. It transposes the voice message from the audio spectrum to the radio spectrum, producing two sidebands while suppressing the carrier. The sideband filter, tuned near the fixed RF oscillator frequency, then removes the unwanted sideband, leaving only one.

The mixer transposes this single-sideband signal to the desired operating frequency by combining it with the VFO (Variable Frequency Oscillator), which allows you to adjust the final transmit frequency. The final amplifier boosts the signal to full power and normally includes SWR protection circuitry to guard against antenna mismatch damage.

3.7 Sound Card Digital Modes B-003-007

Modern amateur radio increasingly uses computer-generated digital modes such as FT8, PSK31, and RTTY. These modes require an interface between the computer and the transceiver, and the sound card is at the heart of that interface.

flowchart LR
  subgraph PC ["COMPUTER"]
    DS["Digital Signal"]
    AI["Audio Input"]
    PTT_C["PTT Control"]
  end
  subgraph SC ["SOUND CARD INTERFACE"]
    DAC["DAC
(Digital-to-Analog)"]
    ADC["ADC
(Analog-to-Digital)"]
    PTT_SW["PTT / T-R
Switching"]
    ISO["ISOLATION
TRANSFORMERS"]
  end
  subgraph TRX ["TRANSCEIVER"]
    MicIn["Audio In
(Mic jack)"]
    SpkOut["Audio Out
(Speaker)"]
    PTT_T["PTT"]
  end
  DS --> DAC --> MicIn
  SpkOut --> ADC --> AI
  PTT_C --> PTT_SW --> PTT_T

Sound card interface connects computer digital modes to a transceiver. Isolation transformers prevent hum and ground loops.

The sound card interface performs several critical functions. It converts the received analog audio signal from the transceiver into a digital signal for the computer (ADC), and conversely converts the digital signal from the computer into an audio signal that can be transmitted (DAC). Most interfaces also switch the transceiver between receive and transmit modes via PTT control.

The interface provides audio frequency coupling between the computer and the transceiver. A critical design element is the inclusion of isolation transformers, which prevent the coupling of the transceiver and computer from introducing hum and interference into the transmitted signals. Without these, ground loops between the two devices can introduce 60 Hz hum.

Some modern transceivers can operate digital modes without a separate sound card because they incorporate an audio codec — a built-in ADC/DAC chip that handles the conversion internally.

3.8 Linear Power Supply B-003-008

A linear power supply converts AC mains voltage into clean, regulated DC suitable for powering radio equipment. It has four stages, each performing a distinct transformation, and understanding their order is a frequent exam topic.

flowchart LR
  AC["AC Mains
120V / 240V"] --> XFMR["TRANSFORMER
Step-down + isolate"]
  XFMR --> RECT["RECTIFIER
AC → pulsating DC"] --> FILT["FILTER
Smooths ripple"]
  FILT --> REG["REGULATOR
Stabilizes voltage"] --> DC["DC Output
13.8V"]
  REG --- HS["HEAT SINK
(dissipates excess)"]

Linear power supply: four stages convert AC mains to clean DC. Overvoltage protection monitors voltage at the OUTPUT OF THE REGULATOR.

The transformer converts AC mains voltage up or down as required and provides isolation from the mains. The rectifier converts alternating current into direct current (pulsating DC). The filter smooths out the pulsating DC by removing ripple. The voltage regulator ensures the output voltage stays constant even when the demand on the supply varies, and it typically requires a heat sink because it dissipates excess energy as heat.

3.9 Yagi Antenna Components B-003-009

The Yagi-Uda antenna (commonly just "Yagi") is a directional antenna widely used on VHF/UHF. A basic 3-element Yagi has three distinct parts: a reflector, a driven element, and a director, all mounted on a supporting boom.

  3-ELEMENT YAGI ANTENNA (Top View)

         REFLECTOR          DRIVEN ELEMENT         DIRECTOR
         (longest)          (connected to           (shortest)
                             feedline)
            |                    |                     |
            |                    |                     |
  - - - - -+- - - - -  - - - -+- - - - -  - - - - +- - - - -
            |                    |                     |
            |                    |                     |
                                 |
                            =====╧=====  (feedline / coax)

  <------------------- BOOM -------------------------->

  Direction of maximum radiation --------------------->
  (towards the director)

  Element lengths:  REFLECTOR > DRIVEN > DIRECTOR
                    (~5% longer)        (~5% shorter)

3.10 Receiver Specifications B-003-010

A receiver's quality is measured by three key specifications: sensitivity, selectivity, and dynamic range. This section also covers bandwidth ordering, filter selection, AGC, and IF frequency calculations.

The Big Three: Sensitivity, Selectivity, and Dynamic Range

Sensitivity is indicated by the RF input signal needed to achieve a given signal-to-noise ratio. A lower number means better sensitivity (e.g., 0.15 uV is more sensitive than 1.0 uV). Selectivity is the ability to separate desired signals from adjacent ones, determined primarily by the IF filter bandwidth. Dynamic range is the ability to handle both very weak and very strong signals simultaneously without distortion.

Bandwidth Ordering

Emission modes from narrowest to widest bandwidth: CW, SSB voice, and FM voice.

Waterfall Display and AGC

A waterfall display (spectrogram) shows two signal parameters: amplitude and frequency. Frequency appears on the horizontal axis, time scrolls vertically, and signal strength is shown by colour/brightness.

Automatic Gain Control (AGC) limits the change in volume due to large signal strength variations. It automatically reduces gain for strong signals and increases it for weak ones, keeping audio output relatively constant.

Tuning Accuracy and Filter Selection

Accurate receiver tuning (within 100 Hz) is most important for SSB mode. If tuned even slightly off, SSB audio sounds unnatural (the "Donald Duck" effect). CW and FM are more tolerant of tuning errors.

Choosing the right filter bandwidth depends on the mode:

IF Frequency Calculation

Bandwidth Tradeoffs

Too narrow a receiver bandwidth causes loss of information — parts of the signal are cut off, reducing intelligibility. Too wide a bandwidth lets in more noise and interference. The art is matching the filter to the mode.

3.11 Modulation Theory B-003-011

Modulation is the process of encoding information onto a radio carrier wave. This section covers the key modulation types (AM, FM, CW), oscillator behaviour, and transmitter efficiency — foundational concepts that tie together many other topics in this guide.

CW Chirp and Oscillator Stability

Chirp is a small change in the output frequency of a transmitter each time a dit or dah is sent. It sounds like the tone is "sliding" at the start of each element. To prevent chirping, you must keep the power supply voltages very steady under varying loads, because voltage changes cause the oscillator frequency to shift.

An RF oscillator should be electrically and mechanically stable to ensure it does not drift in frequency over time. A Variable Frequency Oscillator (VFO) in a CW transmitter offers the advantage that frequency is not constrained to the available crystals — you can transmit on any frequency within the band.

Amplitude Modulation

Amplitude modulation (AM) changes the amplitude of an RF wave to convey information. The instantaneous amplitude (envelope) of the RF signal varies with the modulating audio. Morse code is transmitted by radio as an interrupted carrier — the carrier is switched on and off to form the code pattern, which is the simplest form of modulation.

An AM signal contains a carrier and two sidebands (upper sideband and lower sideband, symmetric around the carrier).

Transmitter Efficiency

Not all the DC power fed to a transmitter's final amplifier becomes RF output. The difference between DC input power and RF output power appears as heat. This is why heat sinks and cooling fans are necessary.

3.12 SSB Operation B-003-012

Operating an SSB transmitter properly requires understanding microphone gain, overmodulation, peak envelope power, and the role of the ALC. Getting these wrong causes "splatter" — interference to stations on nearby frequencies — which is one of the most common complaints in amateur radio.

Microphone Gain and Overmodulation

Peak envelope power (PEP) is the term for the average power during one RF cycle at the crest of the modulation envelope. This is how SSB transmitter power is rated. The usual bandwidth of an amateur SSB signal is between 2 kHz and 3 kHz (approximately 2.4 kHz is typical).

Linear Amplifier and Carrier Suppression

The SSB power amplifier must be linear because voice is unintelligible when amplified by a non-linear amplifier. A non-linear amplifier would distort the varying-amplitude SSB envelope. One advantage of carrier suppression in double sideband transmission is that more of the output power can be put into the sidebands, since no power is wasted on the carrier.

ALC, Mic Gain, and the Balanced Modulator

Microphone gain should be adjusted so that the maximum range on the ALC meter is never exceeded on voice peaks. The Automatic Level Control (ALC) in an SSB transmitter limits the input audio peaks so that the transmitter is not overdriven.

The balanced modulator suppresses the carrier and passes the two sidebands. The sideband filter then removes one sideband. This two-step process is how SSB is created.

SSB Frequency Calculation

3.13 FM Operation B-003-013

FM (Frequency Modulation) is the dominant mode for local VHF/UHF communications. This section covers deviation, bandwidth, the capture effect, and practical operating concerns like distortion and microphone technique.

FM Noise and the Advantage of FM

The loud noise from an FM receiver with no signal is caused by the very large gain of stages ahead of the discriminator. Random noise is amplified to full volume when no signal is present to suppress it — which is why squelch circuits are needed.

FM is best for local VHF/UHF communications because it provides a good signal-to-noise ratio at low RF signal levels. FM has a "threshold effect" where, above a certain signal level, noise practically disappears.

Deviation and FM Bandwidth

Deviation is the term for the change in frequency caused by modulation in an FM transmitter. A higher level modulating signal produces a larger deviation of the carrier frequency — louder voice means a wider frequency swing. If your transmitter is set to 2.5 kHz deviation but the repeater expects 5 kHz, your audio will be low (quiet) because you are under-deviating.

FM Characteristics

If an FM transmitter's microphone fails, it produces an unmodulated carrier (dead carrier, no audio). Phase modulation is most closely related to frequency modulation — in fact, many FM transmitters actually use phase modulation to generate FM.

FM is not used below 28 MHz because the bandwidth would exceed limits in the regulations. HF bands are narrow, and FM's wide bandwidth (10-20 kHz) would take up too much space.

Distortion and the Capture Effect

If your FM transmission is reported as loud and distorted, the most probable cause is speaking too loudly into the microphone (causing overdeviation). When more than one signal is present, the FM receiver demodulates only the strongest signal — this is called the capture effect, a major advantage of FM.

3.14 CW Operation & Accessories B-003-014

Operating CW (Morse code) and voice modes requires understanding keyers, microphones, noise management systems, and transmit/receive switching. This section covers the practical accessories and techniques used in day-to-day station operation.

Electronic Keyer and Microphone Setup

Many operators use an electronic keyer to help form good Morse code characters. The keyer helps by regulating the lengths of the dits and dahs to produce properly-timed code. Before using a microphone for the first time with a transceiver, you should adjust the microphone gain level.

Noise Management

Modern receivers include several noise-reduction systems, each targeting a different type of interference:

VOX, Speech Processor, and T/R Switching

VOX (Voice Operated Transmit) causes a transmitter to automatically transmit when an operator speaks into the microphone, eliminating the need to press a PTT button.

A properly adjusted speech processor improves the intelligibility of your signal by compressing the dynamic range of the audio. On a 100% modulated SSB transmitter, a speech processor will increase the average power (not the peak, which stays the same).

T/R switching enables one antenna to be used for both transmitting and receiving. A dynamic microphone has internal components similar to a loudspeaker (moving coil and diaphragm).

3.15 Digital Modes B-003-015

Digital modes have revolutionized amateur radio, enabling communication under conditions where voice would be impossible. From the ultra-weak-signal FT8 to the reliable messaging of packet radio, digital modes offer capabilities beyond traditional analog modulation.

Digital vs. Analog

Modern digital radio can transmit voice and images because any analog information can be converted to digital data via sampling and quantization. The fundamental difference is that digital data is encoded as discrete pre-agreed values (like 0 and 1), while analog data is continuously variable.

Digipeater and Packet Radio

A digipeater receives digital data and retransmits data marked for retransmission. It is a digital repeater that extends the range of packet radio networks. In packet radio, "network" means a way of connecting packet-radio stations so data can be sent over long distances through multiple digipeaters.

Packet radio is especially useful for emergency communications because it provides reliable messaging (guaranteed delivery or notification of failure) through automatic error checking. Automatic Repeat Request (ARQ) permits error correction — if a received packet has errors, the receiving station automatically requests retransmission.

FT8 and RTTY

Dozens of FT8 communications can occur simultaneously in the space of one SSB signal because of time interleaving of the transmissions. FT8 uses precise 15-second time slots and very narrow bandwidth per signal (~50 Hz). It can work at the lowest signal-to-noise ratio (in a 2500 Hz bandwidth), decoding signals as weak as −20 dB below the noise floor.

When selecting an RTTY transmitting frequency, allow a minimum of 250 Hz to 500 Hz separation from a contact in progress. RTTY signals are narrow (~170 Hz shift), so relatively close spacing is possible compared to voice.

Audio Levels in Digital Modes

To verify your digital mode transmit audio is not excessive, ask a local station to confirm your signal is free of splatter. Feeding excessive audio into the transmitter causes splatter or out-of-channel emissions — the same problem as overdriving SSB.

3.16 Batteries B-003-016

Batteries are essential for portable and emergency operation. Understanding battery types, series/parallel connections, and safety is important for both the exam and practical field work.

Battery Fundamentals

A standard automobile battery supplies approximately 12 volts. A battery has a positive terminal and a negative terminal and is a source of electromotive force (EMF). A battery that can be repeatedly recharged is known as a storage battery (or secondary cell). A lithium-ion battery is also a source of EMF.

Battery Type Comparison

Internal Resistance and Discharge

When a battery supplies current, its terminal voltage drops due to internal resistance. If you exceed the specified current rating, the battery will discharge more rapidly than specified and high discharge rates also reduce the effective capacity.

Series and Parallel Connections

  PARALLEL: Same voltage, capacity ADDS
  +---------+
  | 12V 20Ah+--+
  +---------+  |    Result: 12V, 40 Ah
  +---------+  |    (more runtime, same voltage)
  | 12V 20Ah+--+
  +---------+  |
               +--> Output
  -------------+

  SERIES: Voltage ADDS, same capacity
  +---------+   +---------+
  | 12V 20Ah+-->| 12V 20Ah+--> Output
  +---------+   +---------+
                Result: 24V, 20 Ah
                (higher voltage, same runtime)

Lithium-Ion Safety

3.17 Power Supplies & Mobile Wiring B-003-017

Choosing the right power supply and wiring your mobile installation correctly are practical skills that affect both signal quality and safety. This section covers power supply selection, linear vs. switching designs, mobile wiring, and wire gauge calculations.

Power Supply Quality and Selection

A simple supply using only a transformer, rectifier, and filter capacitor (no regulator) powering a CW transmitter could cause chirp — without regulation, the voltage fluctuates with keying, causing oscillator frequency shifts. A power supply is the device that converts 120 volts AC to 12 volts DC. When selecting a 13.8V DC supply for a transceiver, the most important specification is output current capability — it must supply enough current for the transceiver at full transmit power.

Linear vs. Switching Power Supplies

A linear supply may be preferred because of lower risk of radio frequency noise. The main advantage of switching supplies (apart from efficiency) is reduced physical dimensions and weight.

Mobile Installation

The fuse in the DC line should be located as near to the battery as possible to protect the entire circuit (including the wire itself) from overcurrent. Heavy-gauge wires are used for a 100-watt transceiver's DC connection to minimize the voltage drop. At 13.8V, a 100W radio draws about 22 amperes — thin wires would have excessive voltage drop. The positive lead from the vehicle battery must be fused to prevent an overcurrent situation from starting a fire.

The nominal power-line voltages supplied to homes are 120 volts and 240 volts.

Wire Gauge Calculation

A very loud low-frequency hum on your transmission indicates a problem in the power supply — likely a failing filter capacitor or inadequate regulation.

3.18 Electrical Safety B-003-018

Working with radio equipment means working with potentially lethal voltages and currents. This section covers preventing unauthorized access, recognizing hazards, knowing the critical safety numbers, and responding to electrical emergencies.

Preventing Unauthorized Use

The best way to prevent unauthorized use of your home station is to use a key-operated on/off switch in the main power line. For a mobile station, the best approach is to remove the microphone when you are not using it.

Vehicle Battery and Power Supply Hazards

The electrical hazard from a vehicle starter battery is high short-circuit current — a car battery can deliver hundreds of amperes, enough to weld metal and cause severe burns or fire.

Critical Safety Numbers

  ELECTRICAL SAFETY CRITICAL NUMBERS

  +--------------------------------------------+
  |  LETHAL CURRENT:  20 mA  (0.020 A)        |
  |  HAZARDOUS VOLTAGE:  30 V                  |
  |  VULNERABLE ORGAN:  THE HEART              |
  |  HOUSEHOLD CIRCUITS: 120V / 240V           |
  |  (can deliver MANY AMPERES - always lethal)|
  +--------------------------------------------+

Emergency Response

Power Supply Service

Before checking a fault in a mains-operated power supply, turn off the power and unplug the power cord. The risk of troubleshooting a live power supply is electric shock.

3.19 Station Grounding B-003-019

Proper grounding protects you from electrical shock, prevents RF burns, and provides a path for lightning energy to reach earth safely. Every piece of equipment in your station should connect to a single-point ground system.

flowchart TD
  TX["TRANSCEIVER"] --> GND["SINGLE-POINT
GROUND BUS"]
  AMP["AMPLIFIER"] --> GND
  PS["POWER SUPPLY"] --> GND
  GND -->|"Short, heavy conductor"| ROD["GROUND ROD
(copper-clad steel)"]

All equipment connects to one common ground point, then to earth

Grounding for Safety

For best protection from electrical shock, all station equipment should be grounded. Bonding all ground electrodes together with heavy conductors prevents voltage differences between devices during a lightning strike. Chassis ground terminals on all equipment should be connected to the station's single-point ground — never daisy-chain grounds from one device to another.

Fuse Safety

Ground Rod, Green Wire, and Capacitor Discharge

The best material for a ground rod is copper-clad steel. Steel provides strength for driving into the ground, while copper provides excellent conductivity and corrosion resistance.

The green wire in a three-wire AC line cord should be connected to the chassis. This safety ground ensures the chassis stays at earth potential. The AC ground wire connected to the chassis ensures that the chassis does not become energized if a fault occurs.

RF Burns and Ground Impedance

If you get an RF burn when touching your HF transceiver while transmitting, and your ground wire runs 10 metres to a ground rod, the likely cause is the ground wire has high impedance on your operating frequency. Long ground wires can act as antennas at HF frequencies.

3.20 Lightning Protection B-003-020

This section covers lightning protection for your station and antenna system, plus critical safety practices for working on antenna towers and around antennas.

Protecting Your Station

Ground all antenna and rotator cables when the station is not in use to help protect station equipment and building from lightning damage. Install a lightning surge protector on your transmission line outside, as close to earth grounding as possible.

The best protection from lightning damage is to disconnect all equipment from the power lines and antenna cables. No surge protector is 100% effective against a direct strike.

Tower and Antenna Safety

A horizontal wire antenna should be placed high enough so that no one can touch any part of it from the ground. Outside antennas should be high enough so no one can touch them while you are transmitting to prevent RF burns. Before repairing an antenna, turn off the transmitter and disconnect the transmission line.

For a ground-mounted antenna, the especially important precaution is to ensure people are kept at a safe distance. Directional high-gain antennas should be mounted higher than nearby structures so they will not direct RF energy toward people in nearby structures.

3.21 RF Safety B-003-021

RF safety is about keeping yourself and others at a safe distance from transmitting antennas and understanding how RF energy interacts with the human body. This is critical knowledge for both the exam and safe station operation.

UHF/Microwave Safety

When operating at UHF and microwave frequencies, keep the antenna away from your eyes when RF is applied. When putting up a UHF transmitting antenna, make sure the antenna will be in a place where no one can get near it when you are transmitting. Before removing shielding on a UHF power amplifier, make sure the amplifier cannot be accidentally turned on.

Hand-Held Transceiver Safety

Keep the antenna of a hand-held transceiver away from your head when transmitting to reduce your exposure to radio frequency energy. Position the antenna away from your head and away from others while transmitting.

RF Tissue Effects

Power Density and Distance

Indoor and Dipole Antennas

If using indoor antennas, locate the antennas as far away as possible from living spaces that will be occupied while you are operating. For best RF safety, the ends and centre of a dipole antenna should be located as high as possible to prevent people from coming in contact with the antenna. The ends of a dipole have the highest voltage, making them the most dangerous points for RF burns.

Directional high-gain antennas should be mounted higher than nearby structures so they will not direct RF energy toward people in nearby structures.

Quick Reference Summary