I’ve officially cracked open the books again—this time for the Advanced Amateur Radio Certificate and the CW (Morse code) endorsement. It feels a bit like coming full circle: the kid who once tinkered with circuits and devoured electronics and radio magazines is now diving deeper into the theory, the math, and the hands-on craft that make amateur radio such a fascinating technical pursuit.
Hear my call sign, courtesy of Doug VE3XDB.
The Advanced material opens up everything I love: RF design, linearity, oscillators, filters, EMC, antennas, digital modes, and all the elegant physics that sit just beneath the surface of ordinary voice communication. It’s like pulling back the curtain on how radios really work—something I’ve spent my entire engineering career orbiting around anyway.
And CW? Well, that’s its own kind of magic. Learning Morse isn’t just memorizing dits and dahs; it’s learning to think in rhythm, timing, and sound patterns. It’s equal parts language, music, and meditation. There’s something charmingly old-school about connecting to over a century of radio history, while knowing that the skill is still as relevant today as it ever was. It’s where telecommunications began when Samuel Morse tapped out his first message on May 24th, 1844.
In 1942, with the world deep in the turmoil of the Second World War, telegrams were still one of the fastest and most reliable ways to send important messages. Long before email or mobile phones, a telegram could deliver news across countries in minutes, which made it an essential tool for governments, the military, and families trying to stay connected during uncertain times. AP Photo
Honestly, it feels good to be a student again. To stretch the brain. To wrestle with old and new ideas. To learn a skill that rewards both precision and patience.
Let’s see where this next leg of the journey leads.
There is something quietly consequential about being told you are now authorized to transmit. The amateur radio exam is not especially dramatic in its execution—no fanfare, no ceremony—but it represents a formal transition from observer to participant. Preparing for the exam forced me to revisit fundamentals I hadn’t touched in years, confront gaps I didn’t know I had, and relearn how regulation, physics, and operating practice intersect in a real, shared spectrum. Receiving a call sign is not simply a credential; it is an acknowledgment of demonstrated competence and an assumption of responsibility—one that now shifts the focus from study and preparation to practice, participation, and the discipline of operating well on the air.
I wrote my Basic Certificate exam today, and passed with honours, scoring a 90. It was an exciting and somewhat surreal experience, as I’ve been studying for today since September, having signed up for the RAC course in August. I’m a bit breathless about it, to be honest.
I haven’t tried for my first QSO yet, but I will in the next few days, as soon as I have a moment to myself. I’m going to temporarily set up a log in my study notebook until I can get set up on one of the online logging platforms.
I hope to speak with you soon, on 2 m for now. I’m likely monitoring repeater VE3KSR, or VE3RCK.
When I signed up for the RAC Basic Qualification Certificate Course, I thought I knew what I was getting into. After all, I’ve spent nearly four decades working at the intersection of electrical safety, machinery safety, grounding, bonding, EMC, and functional safety. I’ve designed, tested, troubleshot, audited, and certified systems far more complex than a typical amateur radio station. So I assumed that amateur radio would be a pleasant diversion—a technical pastime with some knobs, some wires, and a bit of ionospheric magic thrown in for good measure.
What I didn’t expect was how profoundly the journey would resonate with parts of my life I hadn’t revisited in years.
Week after week, chapter after chapter, I found myself reconnecting not just with the physics and electronics that hooked me as a young technician at GFC Hammond in 1985, but with a sense of curiosity and wonder that has been quietly waiting for an excuse to re-emerge. I suppose this series has been, in its way, a return home.
From Theory to Practice—and Back Again
One of the most rewarding aspects of this course has been rediscovering how beautifully simple the foundations of radio are, even when the implementations become sophisticated. Whether I was rebuilding my understanding of modulation, unpacking the superhet receiver architecture, or tracing the path of an errant RF current through a grounding system, the same truth kept resurfacing:
Everything in radio is just applied physics—and sometimes applied human nature.
I’ve spent decades building and auditing safety systems in industry, and yet I was still delighted to find that amateur radio is full of the same challenges, failures, and “aha!” moments that define engineering everywhere. A poorly bonded chassis, a quarter-wave ground path that decides to behave like a radiator instead of a conductor, a switching power supply gone feral—none of it is new, but each instance is its own puzzle.
And I do love a puzzle.
A Community Built on Respect, Patience, and Self-Governance
The posts I wrote on the amateur radio code of conduct and the broader ethics of the hobby may be some of the most meaningful pieces in this whole series. That’s partly because so much of my professional life has been about building cultures of safety and responsibility—cultures where people look after each other because the stakes demand it.
Amateur radio is no different. A shared spectrum is, fundamentally, a shared responsibility.
Al Penney’s lectures repeatedly emphasized something that mirrors my experience with international standards work: the system only functions when people behave well, even when no one is watching. You don’t kerchunk the repeater. You don’t monopolize a calling frequency. You don’t ignore the interference you might be causing simply because it’s inconvenient to fix.
Courtesy isn’t just etiquette—it’s a form of engineering ethics applied to on-air behaviour. Given how rare civility can feel in today’s broader social landscape, it’s reassuring to see the amateur radio community still committed to courtesy, etiquette, and decorum as everyday practice.
Learning (and Relearning) with a Beginner’s Mind
I’ve forgotten how refreshing it is to sit on the “student” side again. To wrestle with Q-codes that seem like they should have internal logic (but do not), to memorize band plans that look like someone solved a regulatory Sudoku, to absorb historical quirks that persist simply because they work.
There’s a humility in being a beginner again—a humility I didn’t know I needed. And truthfully? It’s been fun.
I’ve enjoyed every minute of preparing these posts. Writing them forced me to clarify what I thought I knew, dig deeper into what I didn’t, and examine why certain ideas matter—not just for the exam, but for the kind of operator I want to be.
Radio as a Mirror of My Professional World
What surprised me most was how often amateur radio echoed my career in safety:
Grounding and bonding? Familiar territory.
RF exposure limits? A cousin of machinery hazard analysis.
Lightning protection? Indistinguishable from industrial surge management.
EMC troubleshooting? That’s been Tuesday morning for 30 years.
Regulations? I’ve lived inside ISO, IEEE, IEC, CSA, and SCC frameworks for most of my adult life.
In many ways, this journey reminded me that engineering disciplines are not isolated silos. They are different dialects of the same language.
What Comes Next
I’m nearing the Basic exam now, and with it, the formal beginning of a new part of this journey. But even before the call sign appears beside my name, I already feel like I’ve joined a centuries-old conversation—one built across continents, frequencies, and generations of experimenters, tinkerers, and communicators.
This series started as a record of what I was learning. Somewhere along the way, it became something richer: A chronicle of reconnecting—with old skills, old curiosities, and parts of myself I had left dormant.
Once the exam is done, I’ll write a final reflection. After that? Who knows. Maybe I’ll build an antenna. Maybe I’ll chase DX. Maybe I’ll get lost in the waterfall. Maybe I’ll discover something unexpected again.
That’s the magic of radio. You never quite know what’s on the air until you listen.
This post marks the end of my week-by-week write-up of the RAC Basic Qualification Course, but not the end of the journey. As I move toward the exam and eventually onto the air, I’m carrying forward not just the technical lessons from each class, but the curiosity, discipline, and sense of community that make amateur radio such a compelling space. Thanks for following along — and stay tuned for what comes next.
Understanding Amateur Radio Regulations: A Practical Guide for New Operators
Based on Al Penney’s Chapter 17: Regulations Ch17-Regulations
When I started my journey into amateur radio, I expected to spend most of my time thinking about antennas, ionospheric quirks, and how to squeeze the best performance out of a receiver. Instead, I quickly discovered that the regulatory side of the hobby is just as fascinating—and just as essential. As someone who has spent decades navigating complex safety regulations and standards, the regulatory architecture of amateur radio feels surprisingly familiar: international bodies establishing the framework, national authorities implementing the rules, and operators applying them responsibly in the real world.
This post summarizes what I’ve learned from Al Penney’s excellent class material on radio regulations, with some added context from my background in standards development. If you’re studying for your Basic exam—or want to understand the governance that keeps our hobby functional and interference-free—this is a solid foundation.
A Very Short History of Global Telecommunications Regulations
Modern amateur radio regulation didn’t emerge in a vacuum; it came out of a century of international cooperation. As early as 1865, European nations recognized they needed harmonized rules for telegraphy to prevent chaos on the growing international communication networks. The International Telegraph Union—precursor to the modern ITU—was founded that year to standardize equipment, establish operating principles, and create common accounting rules for cross-border telegraph traffic.
With radio’s explosive growth, the International Radiotelegraph Union was formed in 1906, and by 1932 the two bodies merged into the International Telecommunication Union (ITU), which later became a UN specialized agency in 1949. Today, the ITU is responsible for global spectrum coordination, technical standards, satellite orbit assignments, and ensuring that radio services—including amateur radio—can coexist without harmful interference.
For anyone used to ISO or IEC work, the ITU’s processes feel familiar: define the service, allocate frequency bands, establish technical parameters, and make sure administrations enforce compliance.
ITU Regions and Why They Matter
One of the most practical things every amateur should know is that the world is divided into three ITU Regions:
Region 1: Europe, Africa, the Middle East, Russia, Mongolia
Region 2: The Americas (including Canada) and parts of the eastern Pacific
Region 3: Asia-Pacific and Oceania
ITU Regions
These regions determine the band plans we use. If you operate from international waters or airspace, you must follow the plan for the region you’re physically in. Canada’s RBR-4 explicitly notes that an amateur station aboard a ship or aircraft in international space operates under the ITU region rules applicable to its location.
Canadian Band Plan image: RAC
This becomes even more important when travelling abroad. Not all countries permit amateur operation by visitors, and even those that do may require formal authorization.
Canada’s Regulatory Framework: Where ISED Comes In
Here at home, amateur radio is governed under the Radiocommunication Act (1985). Innovation, Science and Economic Development Canada (ISED)—formerly Industry Canada—is the federal authority that manages licensing, equipment certification, and spectrum use. Their mandate goes well beyond amateur radio, covering everything from R&D funding and standards development to economic development, telecom regulation, and competition policy.
Within ISED’s framework, the amateur radio service is defined as:
“…a radiocommunication service in which radio apparatus are used for the purpose of self-training, intercommunication or technical investigation… solely with a personal aim and without pecuniary interest.” —ISED, RIC-3
That last part—without pecuniary interest—is important. Commercial use of the amateur bands is strictly prohibited.
Call Signs: Your On-Air Identity
Call signs are assigned using the ITU’s internationally coordinated system. Prefixes identify the country (e.g., VE or VA for Canada), followed by a numeral indicating the region and a suffix assigned by the national authority. ITU Radio Regulations Articles 19.68 and 19.69 define the global allocation of call sign blocks.
As a new operator, your call sign becomes your name on the air—and yes, you must transmit it at “short intervals” (i.e., not less than once every 30 minutes) during communication (RR 25.9). Automated IDers on repeaters exist for this exact reason.
Operating Abroad: CEPT, IARP, and Reciprocal Privileges
Travel adds another layer of complexity. The European Conference of Postal and Telecommunications Administrations (CEPT), established in 1959, coordinates harmonized operation among its member states. Canada is not a CEPT member, but ISED authorizes Radio Amateurs of Canada (RAC) to issue CEPT and International Amateur Radio Permits (IARP) so that Canadian hams can operate while abroad.
For countries not covered by these arrangements, you must contact the foreign authority directly—typically a relatively simple process today thanks to email and web forms.
And, interesting trivia: a few countries, including North Korea and Yemen, do not permit amateur radio at all.
Third-Party Communications: When Can You Relay?
Most of the time, hams may not transmit traffic on behalf of third parties, especially across borders. However, there is a big exception: emergencies and disaster relief. Both the ITU and Canadian RIC-3 explicitly allow third-party international communication for emergency purposes unless a foreign administration has prohibited it.
This is one of the ways amateur radio continues to serve the public good.
Power Limits, Bandwidths, and Other Technical Requirements
ISED defines the maximum permissible power and bandwidth for each band. One interesting regulatory quirk: for many purposes, ISED defines peak envelope power (PEP) as 2.25 × the transmitter’s DC input.
Some LF and MF bands—such as 137 kHz, 630 m, and 60 m—have very narrow permitted bandwidths, far below the more typical 6 kHz limit for HF. These constraints exist to ensure compatibility with other services sharing the spectrum.
EMC, Interference, and Enforcement
Regulators take interference seriously. In Canada, EMCAB-2 governs electromagnetic compatibility requirements for receivers and sensitive equipment, and field-strength limits can be extremely low—down to 3.16 V/m in some cases.
Penalties for non-compliance exist, and while the monetary amounts may change over time, the principle remains: amateur operators are responsible for ensuring their stations do not cause harmful interference.
What All This Means for New Operators
Amateur radio isn’t just a technical hobby—it’s a self-regulated community backed by a carefully structured mix of international treaties, national legislation, and shared operating practice. Whether you’re experimenting with antennas, joining a net, or working portable from a campsite, every QSO sits atop 150 years of regulatory evolution.
As someone who works in safety and compliance, I find this system elegant. The rules aren’t meant to limit creativity; they’re meant to protect the spectrum so creativity remains possible.
And that’s one of the things I love about this hobby.
That’s the end of this series on the RAC course. I’m now reviewing and preparing for my Basic Certificate exam. Once I finish this part of my journey, I’ll likely write a final reflection. After that? Who knows? Watch this space!
Safety Fundamentals for the New Amateur Radio Operator: A Machinery-Safety Engineer’s View
As I continue my journey into amateur radio, one thing has struck me more than anything else: how familiar so much of this territory feels from decades spent working in machinery safety, electrical safety, bonding, and earthing. Whether I’m assessing a press line in a factory or installing a transceiver in my shack, the underlying principles are essentially the same. You’re still dealing with fault currents, leakage paths, thermal hazards, shock exposure, RF exposure, lightning strikes and the absolute necessity of a well-designed grounding and bonding system for both safety and performance.
Lightning striking buildings, chimneys, and towers during a thunderstorm. image: NOAA
Al Penney’s excellent chapter on safety in the RAC Basic course distills many of these fundamentals for the new amateur operator. What follows is my own take—grounded (pun fully intended) in both the course material and my day-to-day practice in machinery safety.
Why Safety Matters in Amateur Radio
Amateur radio looks deceptively benign from the outside—just a few radios, some feed lines, maybe a tower if you’re lucky. But the risks are very real:
Mains voltage and high-current DC systems
Radio frequency (RF) energy exposure
Lightning surges and induced currents
Grounding and bonding failures
Mechanical hazards from towers and masts
Fire risks from poor wiring or aging equipment
If you’ve spent a career keeping machinery operators out of harm’s way, you quickly recognize that amateur operators can face the same categories of hazards—just scaled differently.
1. Understanding Household and Station Power
Canadian residential electrical systems are built around a 240/120-volt, single-phase, three-wire supply. Two “hot” legs (typically red and black) provide 240 volts between them, and each offers 120 volts relative to the neutral conductor (white). Only the hot conductors are fused or switched—never the neutral.
Older homes can pose surprises: two-prong outlets, ungrounded circuits, knob-and-tube or aluminum wiring, or branch circuits overloaded by modern electronics. All of those bring risks that may only show up under RF load or when connecting a modern transceiver or linear amplifier.
The symptoms of overload are textbook:
Flickering or dimming lights
Warm or discoloured receptacle plates
Frequent breaker trips
Buzzing or crackling outlets
A faint burning odour
Each of these is a warning sign that the branch circuit is under stress. In machinery safety, we teach operators to treat “abnormal” as “unsafe.” The same applies here.
2. Shock Hazards: Understanding the Enemy
We’re conditioned to think of electricity in terms of voltage, but in reality, it’s current that injures or kills. Women and men typically have different thresholds for sensing electrical currents. Women generally have a lower threshold of sensation for electrical currents compared to men, often around 40-43% lower for sensory perception in studies using transcutaneous or surface electrical stimulation[16], [17]. For 60 Hz AC currents through hand contacts, perception thresholds are typically below 1 mA for both genders, with grip contacts as low as 0.4-0.5 mA in adult males and similarly low but slightly reduced in females.[18][19]
Standard electrical safety references indicate:
Perception/sensation: 0.5-1 mA (tingling sensation possible for up to 10 seconds), with women often perceiving at lower levels due to higher sensory excitability [16], [20]
Women show consistently lower sensory thresholds across multiple studies, attributed to neurophysiological differences rather than just skin or adipose tissue [17], [21].
Gender Differences
Studies confirm women require less current for initial sensation (e.g., -43% vs. men) and motor responses, though pain perception at higher levels can be more pronounced in women [16], [22]. These thresholds vary by factors such as frequency (AC 50-60 Hz is more perceptible than DC), contact type (grip vs. tap), skin condition, and the current path through the body, but gender disparity persists [18], [23].
Even small currents can be dangerous:
0.25 mA creates perceptible tingling
10 mA can lock your grip due to muscle tetany
20–50 mA across the heart can cause ventricular fibrillation
>100 mA can cause severe burns and internal injury
IEC TS 60947-1 Electric Shock Zones
At 60 Hz—the frequency of the North American power grid—the human heart is particularly vulnerable because its natural pacing interval is in the same range.
Average values for the threshold of sensation and the “can’t let go” current as a function of frequency. The lower the value, the more sensitive the body is at that frequency. [14, Fig. 4] College Sidekick
The path through the body is also important—this is where the “one hand rule” when working with high voltages comes from.
The pathway of the current through the human body is unpredictable, and pathways through the heart are the most dangerous.
By keeping your left hand in your back pocket while working on energized or potentially energized equipment, you eliminate the possibility of introducing current through your left arm which can then travel through your heart to an exit point. Additionally, using an insulating mat rated for the highest voltage you are likely to encounter can help protect against electric shock hazards.
IEC 61140:2016, Protection against electric shock — Common aspects for installation and equipment [15], provides guidance on measures that can be used to reduce the risk of shock.
The table below shows the defined limits for some of the voltage bands covered in IEC standards. Except for RF voltages appearing on transmission lines and antennas in operation, everything in the radio shack operates at Low Voltage (LV), below 1000 Vac or 1500 Vdc. The CEC in Canada and the NEC in the USA extend down to 0 Vac or dc, while in the EU, the Low Voltage Directive uses 50 Vac or 75 Vdc as the lower limit.
Limits for Voltage Bands (IEC 61140:2016, Table 1)
Damp or wet conditions can reduce the voltage where a shock hazard exists to as little as 6 V.
A helpful formula for estimating shock current is Ohm’s Law:
Ohm’s Law
Where:
I = current through the body
V = applied voltage
R = resistance of the body (which can drop below 1000 Ω when the skin is wet)
Thus, a wet human body touching 120 V can experience:
Far into the range of fatal fibrillation.
The impedance of the body is made up of two components:
Skin resistance
Internal resistance
Both components can include a capacitive element, which becomes more important as the frequency of the electrical source increases.
Current path
Dry skin
Wet skin
ear-to-ear (internal)
100 Ω
left hand to left foot (internal)
500 Ω
left hand to left foot
100 kΩ – 600 kΩ
1 000 Ω
At 500 V or more, high resistance in the outer layer of the skin breaks down.
Ways protective skin resistance can be significantly reduced
• Significant physical skin damage: cuts, abrasions, burns • Breakdown of skin at 500 V or more • Rapid application of voltage to an area of the skin • Immersion in water
Al’s advice mirrors good industrial practice: do not approach a shock victim until the circuit is de-energized. Otherwise, you risk becoming the second casualty.
3. Protective Devices: GFI/GFCI, AFCI, and Isolation Transformers
The basic defence against shock hazards in modern wiring is the Ground-Fault Circuit Interrupter (GFCI). A GFCI compares the current in the hot and neutral conductors. If the currents differ by more than about 5 mA, it assumes leakage—possibly through a human body—and disconnects the circuit.
The underlying principle can be expressed as:
Whenever:
—the GFCI trips.
Similarly, the Arc-Fault Circuit Interrupter (AFCI) recognizes series and parallel arcing signatures in conductors—important because many residential fires start with an arc in damaged or aging wiring.
An isolation transformer adds another layer of protection by preventing current from finding a return path through the earth or through a person. In machinery safety, isolation is fundamental for service procedures; the same applies when working on radios.
4. The Three Grounds Every Station Needs
Lightning grounding system
Al Penney introduces three distinct ground types for amateur stations:
AC Safety Ground The protective earth connection required by electrical codes. This ensures exposed metal stays at earth potential during a fault.
Lightning Ground Provides a low-impedance path to earth for lightning-induced surges, protecting the structure and equipment.
RF Ground Provides a low-impedance path at radio frequencies, minimizing RF feedback, interference, and hot spots.
In machinery safety, we typically talk about earthing (fault protection) and bonding (equipotential equalization). Amateur radio requires both, but adds RF behaviour to the equation.
Antenna and starion bonding and grounding image: Mike Mikelson
Bonding vs. Grounding (Earthing)
An exothermically welded bonding connection to a ground rod
Bonding is the practice of connecting metal components to maintain equipotentiality as much as possible.
Grounding/Earthing connects the system to the earth reference.
An amateur station must do both; otherwise, circulating currents will cause unpredictable (and occasionally unpleasant) results.
5. RF Grounding: The Hidden Trouble-Maker
Unlike AC grounding systems, RF grounds behave according to wavelength. A conductor approaching ¼ wavelength at the operating frequency becomes a high-impedance point:
Where
λ = wavelength in metres
c = speed of light in a vacuum (300,000,000 m/s)
f = frequency
For example, at 14 MHz (20-metre band):
A quarter-wave is roughly:
A ground strap >5 m long may actually create an RF hotspot rather than eliminate one.
This is why the single-point ground (SPG)—a central bonding bar to which all equipment is connected—is so important. It minimizes circulating currents, reduces RF feedback, and prevents your rig’s microphone or your metal desk from becoming unexpectedly “hot.”
6. Ground Rods and Earth Systems
From a machinery-safety perspective, ground rods in a radio installation behave exactly like the electrodes used in industrial and utility installations. The fundamentals are the same:
Use copper-clad steel rods
Length matters (2.4–3.0 m recommended)
Use UL-listed or CSA-marked clamps
Use heavy copper conductors (#6 AWG or tinned copper strap)
Bond cold-water piping only if it is metallic and continuous
But the CEC requires that all grounding electrodes—service ground, lightning protection ground, and any supplemental rods—must be bonded together. Failure to bond grounds is one of the leading causes of destructive surge paths.
7. Lightning Protection: Voltage Equalization is Everything
A lightning strike doesn’t need to hit your tower directly to ruin your equipment. A near strike can induce thousands of volts into cables or wiring. The goal isn’t to “block” lightning—that’s impossible—but to:
Bring every conductor entering the house to the same potential
Provide a low-impedance path to earth
Prevent flashover inside the structure
This is exactly how industrial surge protection works in machinery with long interconnecting cables.
For amateurs, this means:
Bonding coax shields at the service entry
Using spark gaps or gas discharge tubes
Keeping bends in ground conductors smooth and gentle
Bonding the tower to the station ground system
Keeping the entry panel (or bulkhead) as close to the station ground as practical
The theme is always the same: equipotential bonding.
8. RF Exposure: What New Operators Need to Know
Radio frequency exposure is regulated because non-ionizing radiation (NIR) can heat tissue, stimulate nerves, and cause cataracts or burns at sufficiently high power densities.
In Canada, we follow Health Canada’s Safety Code 6, Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency Range from 3 kHz to 300 GHz [33]. This document sets out, in technical terms, the maximum exposure levels that humans can tolerate without causing identifiable harm.
SC6 does not define transmitter power, or effective radiated power (ERP), but rather the intensity of the E- and H-fields. E-fields are measured in volts per metre (V/m) at a specific distance from the source, and H-fields are measured in amperes per metre (A/m). Table 1 from SC6 gives the maximum exposure limits for individuals including occupationally exposed workers and the general public.
Note that the exposure limits in Table 1 are much lower in the Uncontrolled Environment (i.e., the general public) than those in the Controlled Environment (i.e., workers in RF exposed environments).
[33][33][33]
The basic field-strength relationship is:
Where:
S = power density
PTX = transmitter power
G = antenna gain (linear)
r = distance from antenna
Even a 100-watt HF radio can exceed allowable limits if the antenna is too close or improperly installed.
In addition, SC6 includes limits for induced and contact currents as shown in Tables 7 and 8. Induced currents can cause RF shocks and burns.
SC6 has not been updated since 2015, however, the International Commission on Non-Ionizing Radiation Protection published the Guidelines for Limiting Exposure to Electromagnetic Fields (100 kHz to 300 GHz) [34] in 2020.
The new ISED exposure rules require:
Station evaluation
Control of uncontrolled (public) vs controlled (licensee) areas
Documentation
It’s not onerous—but it needs to be done.
9. Fire Safety, Surge Protection, and Aging Equipment
Surge protectors degrade with every transient. The metal-oxide varistor (MOV) inside slowly changes its characteristics until it fails—sometimes due to overheating. That’s why a surge protector should always have:
A functioning status indicator
Internal over-current protection
Adequate joule rating (≥600 J preferred)
Proper UL/CSA marking
As Al notes, “daisy chaining” power strips is a known fire hazard. And in a station environment, power strips often operate near their limits due to radios, chargers, tuners, and amplifiers.
If something feels warm under normal load, it’s already trying to tell you something.
Fire safety
If you are finishing a basement room for use as a radio shack, consider installing a smoke/CO2 detector in the shack, even if there is another one in the basement. This will allow you to close and lock the door when not in use or when kids are around, preventing accidents and unauthorized use of the equipment.
Having a suitable fire extinguisher in the shack is important in case something does catch fire. Either a Type A and Type C extinguisher or a multi-type extinguisher intended for those types of fires should be kept on hand and inspected monthly.
10. First Aid: The Human Side of Electrical Safety
One of the best lines in Al Penney’s chapter is simple:
Do not approach until the power is off. —Al Penney, VO1NO
Everything after that follows the standard chain of survival used in industrial electrical incidents:
Ensure the scene is safe
Disconnect power
Call 911
Provide CPR and use an automated external defibrillator (AED) if available
Treat for shock and burns
It’s worth taking a CPR/AED course—whether for radio, machinery safety, or life in general.
Conclusion: Amateur Radio Safety Is Just Engineering Done Right
One of the reasons I’m enjoying amateur radio so much is that it brings together every part of my engineering background—electrical safety, bonding and grounding, RF, EMC (electromagnetic compatibility), and yes, even some human factors. The same principles that keep machine operators safe apply in the radio shack:
Keep conductive parts at the same potential
Control fault paths
Expect insulation to fail eventually
Keep conductors short and low-impedance
Let protective devices do their job
And above all—respect electricity
Of course, there’s a lot more to say about safety: tower climbing, RF exposure, etc. Safety isn’t a checkbox; it’s a mindset. And as new amateur operators, embracing that mindset early keeps our stations—and ourselves—operating for years to come.
Bibliography
[1] A. Penney, Safety. Royal Amateur Radio Club (RAC) Basic Qualification Course, Chapter 16, VO1NO, n.d. Ch16-Safety
[2] National Fire Protection Association (NFPA), “Home Electrical Fires,” NFPA Reports, 2010.
[3] Electrical Safety Foundation International (ESFI), “Fuse and Breaker Breakdown,” “Switch to Safety,” and “Extension Cords and Power Strip Safety,” ESFI Resources. [Online]. Available: https://www.esfi.org/
[5] Mayo Clinic Staff, “Electrical injuries: First aid,” Mayo Clinic, 2019.
[6] “How to Treat a Victim of Electrical Shock,” WikiHow, 2023.
[7] Hydro-Québec, “What are the effects of electric current on the human body?” Hydro-Québec Safety Resources, 2018.
[8] M. Holt, “Electrical Shock Hazards Explained,” Mike Holt Enterprises, 2002.
[9] Centers for Disease Control and Prevention (CDC), “Worker Deaths by Electrocution,” NIOSH Publication 98-131, 1998.
[10] Reader’s Digest, “CPR 101: These Are the CPR Steps Everyone Should Know,” Reader’s Digest Canada, 2021.
[11] F. Pantridge, “Portable Defibrillation: Early Development and Clinical Use,” Lancet, vol. 286, no. 7424, 1965.
[12] Underwriters Laboratories (UL), UL 1449 – Standard for Surge Protective Devices, 4th ed., UL, 2014.
[13] American Heart Association (AHA), “Hands-Only CPR Guidelines,” AHA CPR & First Aid, 2020.
[14] ‘Electric Hazards and the Human Body’, College Sidekick — Physics. [Online]. Available: https://www.collegesidekick.com/study-guides/physics/20-6-electric-hazards-and-the-human-body
[15] Protection against electric shock — Common aspects for installation and equipment, IEC 61140. Geneva: International Electrotechnical Commission (IEC). 2016.
[16] Differences in electrical stimulation thresholds between … https://pubmed.ncbi.nlm.nih.gov/18300313/
[17] Differences in electrical stimulation thresholds between men and women https://onlinelibrary.wiley.com/doi/10.1002/ana.21346
[18] J. C. Keesey, F.S. Letcher. “Human Thresholds of Electric Shock at Power Transmission Frequencies.” Arch. Env. Health. Vol. 21. 1970. Available: https://zoryglaser.com/wp-content/uploads/2020/05/HUMAN-THRESHOLD-OF-ELECTRIC-SHOCK-AT-POWER-TRANSMISSION-FREQUENCIES.pdf [Accessed 2025-11-30]
[19] Minimum Thresholds for Physiological Responses to Flow of Alternating Electric Current Through the Human Body at Power-Transmission Frequencies, Naval Medical Research Institute. 1969. Available: https://zoryglaser.com/wp-content/uploads/2020/05/MINIMUM-THRESHOLDS-FOR-PHYSIOLOGICAL-RESPONSES-TO-FLOW-OF-ALTERNATING-ELECTRIC-CURRENT-THROUGH-THE-HUMAN-BODY-AT-POWER-TRANSMISSION-FREQUENCIES-NMRI.pdf [Accessed: 2025-11-30]
[20] Safe Levels of Current in the Human Body Available: https://www.d.umn.edu/~sburns/EE2212/L-Safe-Levels-of-Current-in-the-Human-Body.pdf [Accessed 2025-11-30]
[21] Sex and age differences in sensory threshold for … Available: https://www.scielo.br/j/fm/a/FkPdhzvxmxLcZ7QXjsjCGLz/?format=pdf&lang=en [Accessed 2025-11-30]
[22] Differences in electrical stimulation thresholds between … Available: https://onlinelibrary.wiley.com/doi/abs/10.1002/ana.21346 [Accessed 2025-11-30]
[23] Let Go Current | IE Rule – Estimation and Costing Available: https://www.electricalje.com/2024/12/let-go-current-ie-rule-estimation-and.html [Accessed 2025-11-30]
[24] “Gender Differences in Current Received during Transcranial Electrical Stimulation”. Frontiers. Available: https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2014.00104/full [Accessed 2025-11-30]
[25] “HUMAN RESPONSES TO ELECTRICITY “. Available: https://ntrs.nasa.gov/api/citations/19730001338/downloads/19730001338.pdf [Accessed 2025-11-30]
[26] “Factors Affecting and Adjustments for Sex Differences in Current Perception Threshold With Transcutaneous Electrical Stimulation in Healthy Subjects”. Available: https://onlinelibrary.wiley.com/doi/full/10.1111/ner.12889 [Accessed 2025-11-30]
[27] “The effects of high electric current on the human body”. Available: https://betacomearthing.com/resources/the-effects-of-high-electric-current-on-the-human-body/ [Accessed 2025-11-30]
[28] E. Dölker, S. Lau, M. A. Bernhard, J. Haueisen. “Perception thresholds and qualitative perceptions for electrocutaneous stimulation”. Available: https://pmc.ncbi.nlm.nih.gov/articles/PMC9072403/ [Accessed 2025-11-30]
[29] “AC & DC Electric Shocks – Electrical Energy in the Home”. Available: https://eliotsphysics.weebly.com/ac–dc-electric-shocks.html [Accessed 2025-11-30]
[30] S. Seno, H. Shimazu, E. Kogure, A. Watanabe, H. Kobayashi. “Factors Affecting and Adjustments for Sex Differences in Current Perception Threshold With Transcutaneous Electrical Stimulation in Healthy Subjects”. Available: https://pmc.ncbi.nlm.nih.gov/articles/PMC6766980/ [Accessed 2025-11-30]
[31] I. Lund, T. Lundeberg, J. Kowalski, L. Svensson. “Gender differences in electrical pain threshold responses to transcutaneous electrical nerve stimulation (TENS)”. Available: https://pubmed.ncbi.nlm.nih.gov/15670645/ [Accessed 2025-11-30]
[32] “Characteristics of current perception produced by intermediate-frequency contact currents in healthy adults”. Frontiers. Available: https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1145505/full [Accessed 2025-11-30]
Wrestling with the Noise: What I Learned About Radio-Frequency Interference
Reflections on Chapter 15 of Al Penney’s RAC Basic Course
Anyone who has spent time on the air will eventually run head-first into radio-frequency interference (RFI)—and usually at the worst possible time. You finally settle into a good QSO, or you’re testing a new antenna, and suddenly the bands dissolve into a wall of buzz, crackle, or inexplicable signals that have no business being there.
For me, these problems are more than just an occasional amateur-radio annoyance—they echo challenges I’ve dealt with for decades in my professional life. My work in machinery safety involves electromagnetic compatibility (EMC) testing, troubleshooting, and ensuring compliance with a wide range of functional-safety standards. In the world of machinery, poorly controlled electromagnetic phenomena can have far more serious consequences than a ruined QSO: they can shut down production lines, disable safety-related parts of control systems, or jeopardize the performance of SIL-rated and PL-rated safety functions. Understanding how interference couples, propagates, and affects equipment has been part of my daily toolkit for years.
So when Al Penney covered RFI and EMI in the RAC Basic course yesterday [1], it felt like familiar territory—but with a distinctly amateur-radio flavour. The chapter blended physics, practical engineering, and station-craft in a way that resonated deeply with my EMC experience. As someone who cares about both signal integrity and functional safety, this was immensely satisfying—and a potent reminder that good EMC practices are universal, whether you’re safeguarding a press-brake control system or keeping an HF rig clean on 20 metres.
Below are my takeaways, with plenty of technical depth for those who enjoy understanding the “why” behind the “what,” and hopefully helpful guidance for newcomers wrestling with their first tangle of interference.
The Two-Sided Nature of RFI
Al broke the entire problem down into two buckets:
Interference your station causes to others
Interference caused to your station by other devices
The most sobering part? Most cases of interference can be cured, but almost never by arguing about blame. You have to consider both the equipment and the humans involved. Al’s reminder to approach every RFI complaint with “calm, empathy, and cooperation” should be etched on every ham’s shack wall.
RFI vs EMI: Getting Our Terms Straight
Sources of RFI and EMI
We often throw “noise” around as a catch-all term, but the distinctions matter.
Radio-Frequency Interference (RFI) is interference in a receiver caused by unwanted signals (only one of which is desired).
Electromagnetic Interference (EMI) is RF energy that affects equipment not intended to receive RF, such as machinery, appliances, furnaces, smoke detectors, thermostats, speakers, telephones, and computers.
When RF bullies its way into the front end of a device through inadequate shielding or filtering, you get EMI.
It’s also worthwhile remembering that, depending on the source you read, RF is the Extremely Low Frequency (ELF) band, which is defined as ranging from 3 to 30 Hz by the International Telecommunication Union (ITU) and other major standards bodies, with corresponding wavelengths from 100,000 km down to 10,000 km. However, Very Low Frequency is the lower end of the RF spectrum and the range used by practical radio transmission systems, spanning 3 kHz to 30 kHz. Happily, none of these frequencies are included in the amateur bands.
Four Core Types of Interference
Al identified four primary mechanisms that create RFI/EMI problems:
1. Noise
External noise from electrical systems—motors, switching supplies, furnace igniters, fluorescent lighting, thermostats, dimmers—creating broad-spectrum buzzes and raspy signatures across HF.
These often show up as wideband trash rather than discrete signals. Identification usually means turning things off one by one until the culprit reveals itself. Al suggested that you can start by turning off the main switch in your home to see if the noise disappears. If so, you have to go through each circuit in your home to find the culprit.
2. Fundamental Overload (FO)
This is one of the most common problems. Fundamental overload (FO) occurs when a strong RF signal overwhelms the receiver’s front end, which lacks sufficient filtering.
It’s fascinating how stark the physics are. The strength of the interfering signal follows the inverse-square law, modelled as:
If you consider a sphere surrounding the point source in the diagram above, the area of the inside of the sphere is defined by
Where:
S(r) = power flux density at distance r (W/m²)
PTX = RF power delivered to the antenna (W)
G = antenna gain referenced to an isotropic radiator (dimensionless, not in dBi)
At radius r from the source, a certain intensity exists on the surface of the sphere, I, which is measured in volts per metre (V/m). At 2r, the intensity according to the formula above is now 1/4I, and at 3r it falls to 1/9r. Even doubling the distance between two houses can reduce the interfering field strength to one-quarter. Of course, moving your neighbour’s house farther away from your antenna may be difficult, so it’s likely easier to move your antenna 😀.
3. Cross Modulation (XM)
Cross modulation (XM) occurs when a strong AM-type signal is rectified at some stage of a receiver, imposing its modulation on another signal.
This is most noticeable on AM broadcast receivers, but the presentation reminded me of the old NTSC TV days, when strong local signals produced ghosting artifacts.
4. Intermodulation Distortion (IMD)
Intermodulation distortion (IMD) is the mixing of two or more signals in a nonlinear device, producing sum and difference frequencies:
A common nuisance is the third-order IMD:
These often fall near the desired signal and can be nearly impossible to filter out, especially in dense RF environments like 2 m FM repeaters downtown.
Spurious Emissions: When the Transmitter Misbehaves
Even well-designed transmitters generate small amounts of harmonics and other spurious emissions.
Harmonics occur at integer multiples of the fundamental:
Where
f0 = operating frequency
n = harmonic number
The 2nd and 3rd harmonics are typically the strongest.
Good transmitter design—combined with proper station grounding and not over-driving an amplifier—keeps these suppressed well below regulatory limits.
The Role of the Source–Path–Victim Model
One of the most elegant conceptual tools in the chapter is the source–path–victim model. Every EMI problem requires:
A source of RF energy
A path (radiated, conducted, or induced)
A victim device susceptible to that energy
Noise Coupling Mechanisms
Radiation Coupling
Radiation coupling is the form of RFI most amateurs and engineers encounter: electromagnetic energy simply travels through free space from the source to the victim device. Because it doesn’t rely on any physical connection, it can affect equipment over surprisingly long distances, especially in RF-dense environments such as industrial plants, telecom sites, hospitals, or any setting where multiple transmitters and sensitive receivers share the same airspace.
Conduction Coupling
Conduction coupling occurs when unwanted RF energy hitches a ride along conductive paths—power wiring, signal lines, control cables, grounding conductors, or any metal that forms a continuous path between the source and the affected device. This is a common issue in machinery and building wiring, where poor cable management, inadequate bonding, or inconsistent shielding allow interference to propagate directly into sensitive electronics. Good grounding practice, proper cable segregation, and high-quality shield terminations are essential tools for controlling conducted RFI.
Capacitive Coupling
Capacitive coupling occurs when an electric field from an interference source induces charge to flow into an adjacent conductor or circuit. This mechanism becomes especially troublesome when components or cables are routed close together—such as neighbouring PCB traces, bundles of control wiring, or harnesses inside industrial enclosures. Thoughtful layout, appropriate separation, and maintaining proper insulation or shielding significantly reduce the risk of RFI coupling through stray capacitance.
Magnetic Coupling
Magnetic (inductive) coupling occurs when a varying magnetic field induces voltage into nearby conductors, particularly loops or long parallel runs. This is the mechanism behind many audio rectification problems, transformer hum issues, and interference in industrial control circuits. Twisted-pair cabling, increased spacing, minimizing loop area, and adding magnetic shielding are proven strategies to limit inductive coupling and maintain the integrity of both communication and safety-related signals.
Real-world problems
Most real-world problems involve multiple paths. For example:
RF radiates from your antenna
It couples into your neighbour’s speaker wires
The wires conduct it into a cheap audio amplifier
A transistor rectifies the RF and produces audible audio
Until you identify the correct path, you’re just throwing ferrites into the void.
Differential Mode vs Common Mode: Why Ferrites Work (or Don’t)
The distinction between differential-mode (DM) and common-mode (CM) currents is key to understanding how to solve interference problems.
DM currents flow out on one conductor and back into the other.
Filters solve DM.
CM currents appear equally on multiple conductors and typically return via ground.
Ferrite chokes solve CM.
A single filter type cannot fix both. Many new hams attack CM problems with DM filters and end up frustrated.
Cleaning Your Own House First
Not my shack, but it’s nice and neat!
One of the most important practical lessons: before helping anyone else with RFI, make sure your own station is clean.
Tighten every connector
Bond the equipment to a single-point ground
Add a low-pass filter (LPF) on HF transmitters
Ensure proper coaxial routing and no sharp bends
Avoid over-driving microphones or amplifiers
Keep a tidy, professional-looking station (this is diplomacy!)
Nothing inspires confidence like demonstrating your own trouble-free system.
Filters, Ferrites, and Other Tools in the RFI Toolkit
Low-Pass Filters (LPF)
Used on HF transmitters to block harmonics above the cutoff frequency.
High-Pass Filters (HPF)
Useful for TV interference, passing UHF/VHF while attenuating HF and strong low-frequency fundamentals.
Band-Pass, Band-Reject, and Notch Filters
Situational, but powerful when eliminating narrow interference bands.
Quarter-Wave Stub Filters
These are elegant and surprisingly effective. Their length is given by:
Where
c = speed of light
f = frequency
Vf = velocity factor of the cable
They create a deep notch at the design frequency and weaker notches at odd harmonics.
Ferrites (the ham’s best friend)
Ferrite chokes suppress common-mode currents on:
Speaker wires
HDMI cables
CATV coax
USB cables
Power cords
Audio interconnects
Ferrites are simple, cheap, and remarkably effective.
TVI, Audio Rectification, and Troubleshooting Strategies
Television interference (TVI) and audio rectification are classic RFI battlegrounds.
Speaker leads are particularly problematic because:
They’re long
They’re often resonant on HF
They connect directly to output transistors
Negative feedback loops re-inject rectified energy
A simple test: swap the speakers for a pair of short-lead headphones. If the interference vanishes, ferrites on the speaker wires are almost guaranteed to solve it.
Cable TV: Blessing and Curse
Cable systems should shield against ingress and egress. In reality, corrosion, bad connectors, and poor workmanship create unintended long wires that pick up RF beautifully.
For CATV interference, the first line of defence is always a common-mode choke on the CATV coax
If that fails, it may be a direct pickup issue inside the TV set—something only the manufacturer can truly fix.
Grounding: A Double-Edged Sword
Grounding is essential for safety and lightning protection, but long RF grounds—especially at VHF or UHF—can turn into magnificent radiators.
A “ground” that’s several wavelengths long is just an antenna with a superiority complex.
The key is single-point bonding and keeping ground lengths as short as practical.
Station bonding and grounding image: Ward Silver [5]Example of a station grounding blockAntenna and starion bonding and grounding
image: Mike Mikelson [6]
Dealing with Neighbours: The Human Side
Image: [4]
Al spent a surprising amount of time on interpersonal skills—and rightly so.
When someone complains:
Stay calm
Express concern
Explain the issue in simple terms
Avoid blaming their equipment
Offer to test collaboratively
Never open or modify their gear
If the fault isn’t yours, your role becomes “locator of solutions,” not “provider of unauthorized repairs.”
Done right, you transform from “the guy causing problems” to “the neighbour who helps solve them.”
Final Thoughts
This chapter was one of the best blends of physics, practical engineering, and human communication I’ve encountered in the RAC course so far. RFI isn’t just about circuits—it’s about relationships, systems thinking, and methodical troubleshooting.
As someone who enjoys both the science and the diplomacy of amateur radio, I came away from Al’s session energized and better equipped—not just to solve interference, but to prevent it, understand it, and teach others about it.
And with the RF environment becoming more hostile every year, these skills matter more than ever.
Bibliography
[1] Al Penney, Radio Frequency Interference, RAC Basic Qualification Course, Chapter 15, Radio Amateurs of Canada, 2025.
[2] ‘Types, Uses, and Benefits of RF Shielding’. Accessed: Nov. 18, 2025. [Online]. Available: https://www.iqsdirectory.com/articles/emi-shielding/rf-shielding.html
[3] T. Ellison, ‘Grounding Systems in the Ham Shack – Paradigms, Facts and Fallacies’, Flex Radio. Accessed: Nov. 18, 2025. [Online]. Available: https://helpdesk.flexradio.com/hc/en-us/articles/204779159-Grounding-Systems-in-the-Ham-Shack-Paradigms-Facts-and-Fallacies
[4] ‘Anger as Man Working From Home Demands Neighbors’ Kids Play Inside’, Newsweek. Accessed: Nov. 18, 2025. [Online]. Available: https://www.newsweek.com/anger-man-working-home-demands-neighbors-kids-play-inside-1732472
[5] W. Silver, N0AX, ‘Ham Radio Tech: RF Management–In the Field’, OnAllBands. Accessed: Nov. 24, 2025. [Online]. Available: https://www.onallbands.com/ham-radio-tech-rf-management-in-the-field/
[6] M. Mikelson, KD8DZ, ‘When Lightning Strikes — Grounding for Amateur Radio Stations’, Feb. 25, 2024.
Tuning In: What I Learned About Radio Receivers from Al Penney’s Chapter 14
A vintage Trio TS-530S HF transceiver. Image: John Parfrey.
If you’ve been following my ham-radio learning journey, you already know that every week I come away from Al Penney’s RAC Basic class with at least one “aha!” moment. Chapter 14—Radio Receivers—was no exception. In fact, this one took me right back to 1985, when I was sitting at my test bench on the GFC Hammond shop floor with a scope probe in my hand, trying to figure out why a switching supply refused to behave.
Receivers, it turns out, aren’t that different: they’re equal parts physics, architecture, and black-magic engineering. What follows are my notes and reflections on what Al covered—sensitivities, selectivities, superhets, noise sources, and that never-ending problem of intermod and cross-modulation that haunts every urban ham.
What a Receiver Actually Has to Do
I think most non-hams imagine a radio receiver as a kind of magical ear—just “listening” to signals floating around. In reality, it’s a chain of brutally practical engineering steps:
Capture the RF using the antenna
Select the one frequency we care about from thousands across the spectrum
Amplify it without adding too much noise
Recover the modulation—audio, data, or whatever information was riding on the carrier
Amplify the audio and send it to a speaker, headphones, or computer interface
Each block in that chain is an opportunity to either improve fidelity or seriously mess things up.
This is why receiver performance is usually described by the “three Ss + D”: Sensitivity, Selectivity, Stability + Dynamic Range [1].
Sensitivity: Hearing Signals That Barely Exist
One of the wildest things about radio is just how small the signals are. At the antenna terminals, we’re often dealing with femtowatts—10-15 watts—yet after running through the receiver chain, we expect clean audio at the speaker.
In modern HF rigs, sensitivity is rarely the limiting factor anymore. Al pointed out that, using SSB, the Kenwood TS-890 reliably hears down to 0.2 µV between 1.7 and 24.5 MHz [1]. That’s astonishing.
But sensitivity ultimately runs into physics:
Below ~30 MHz, the natural noise floor dominates.
In other words, there’s no point trying to design an HF receiver with another 6 dB of sensitivity—galactic noise, atmospheric noise, and man-made noise swamp the front end long before the Low-Noise Amplifier (LNA) does.
A few key measurements I found interesting:
Noise Figure (NF) – becomes critical at VHF/UHF where sky noise drops dramatically
MDS (Minimum Discernible Signal) – usually around −120 to −130 dBm for a good HF rig in 500 Hz BW
SNR and SINAD – important especially for FM receivers
Signal-to-Noise And Distortion (SINAD):
Where
S = Signal
N = Noise
D = Distortion
expressed in decibels (dB).
Al Penney’s material notes:
For a VHF or UHF receiver, SINAD is typically around 12 dB for an input of 0.25 µV (≈ −119 dBm).
This is the standard sensitivity measurement used in commercial and amateur FM equipment.
At VHF/UHF, the internal noise of that first transistor—your LNA—sets the limit. HF? Not so much.
Selectivity: Where the Adults and Children Separate
Selectivity is the receiver’s ability to separate two closely spaced signals. And this, more than raw sensitivity, is what earns premium radios their price tag.
Al made a comment I loved:
Filter skirt steepness is what separates the adults from the children in HF receiver design. [1]
The skirts—the shape of the filter’s passband edges—determine how well a receiver rejects adjacent-channel interference. A typical SSB filter might have:
–6 dB bandwidth: ~2.3 kHz
–60 dB bandwidth: ~3.3 kHz
A shape factor near 2:1 at 6/60 dB is excellent.
Receiver Selectivity
It’s worth appreciating just how much of our “receiver experience” is determined by these numbers. A crowded contest weekend on 20 m can turn a mediocre receiver into a miserable one.
Digital Signal Processing (DSP) helps—adjustable bandwidth, notch filters, noise reduction—but the basic physics still matter.
Stability: The End of Drifty Radios
Anyone who has ever used an old tube rig on CW knows the pain of “chasing” your signal up or down the band as the oscillator warms up.
Drift simply isn’t a major issue anymore. Modern PLL and DDS synthesizers with temperature-compensated oscillators typically achieve stability in the low parts-per-million (ppm) range [1].
What DDS Does
A DDS system creates RF signals digitally by:
Using a numerically controlled oscillator (NCO)
Stepping through a digital sine wave lookup table
Converting the digital waveform to analog using a DAC (Digital-to-Analog Converter)
Filtering the output to produce a clean RF signal
This allows the radio’s VFO to tune in extremely fine steps (often <1 Hz) with excellent frequency stability.
Why Radios Use DDS
Compared with older analog VFOs or PLLs, DDS offers:
Very high frequency stability
Extremely fine tuning resolution
Fast frequency changes (great for scanning or DSP features)
Low drift, because it ultimately relies on a stable reference oscillator
Ability to implement complex waveforms (FSK, PSK, chirps)
Still, your VFO is only as good as its reference. If the radio’s timebase drifts, so does every displayed frequency. That’s why Al reminded us to check against WWV, WWVH, or CHU periodically.
Dynamic Range
Although it doesn’t get listed alongside Sensitivity and Selectivity, the Dynamic Range of a receiver is every bit as important. It describes, in dB, the span of signal levels over which the radio can still do its job—pulling out the signals we actually care about without collapsing under the load. On the ham bands, this really matters because we routinely deal with whisper-weak signals sitting right beside blowtorch-strong ones, and a receiver with poor dynamic range simply can’t cope. There are a few different ways to measure it, but the rule of thumb is simple: the higher the dynamic range, the better the receiver will behave in real-world conditions.
Cross-Modulation and Intermod: The Curse of Strong Signals
Urban hams know this pain well: you’re trying to listen to a clean signal on 146.97 MHz, but the local taxi dispatcher or paging transmitter blasts into your receiver anyway.
Two related but distinct demons cause this:
Cross-modulation
A strong AM signal overloads the front end, causing its modulation to appear on your desired signal. It shows up when:
You’re close to a high-power AM broadcast tower
Your front-end LNA is being driven into nonlinearity
Attenuators help. So do front-end filters.
Intermodulation (IMD)
Two (or more) strong signals mix inside a nonlinear junction—an RF transistor, a mixer, even a rusty fence. This produces:
f1 ± f2
2f₁ ± f₂
2f2 ± f1, etc.
On 2 m and 70 cm FM, IMD is especially brutal when driving through downtown due to the density of transmitters [1].
A high third-order intercept point (IP3) is your best defence.
A high IP3 is one of those specs that separates a decent receiver from a truly capable one. It’s a measure of how linear the receiver is—basically, how well it can deal with strong nearby signals without creating its own intermodulation junk. When multiple strong signals are floating around just outside your passband, a receiver with good IP3 will stay composed; a poor one will start generating intermod products that show up as false signals and make life miserable.
The higher the IP3, the more signal the front end can tolerate before nonlinearities kick in and begin creating interference that wasn’t actually there. In real operating conditions—especially in busy urban RF environments or during contests—high IP3 performance is your best defence against overload, distortion, and those phantom signals that clutter up the band. It’s a key part of keeping the receiver clean, stable, and able to pull in the signal you actually care about.
Explanation of Third-Order Intercept Point (IP3)
IP3 is a theoretical power level where the power of the third-order intermodulation products theoretically equals the power of the desired signal.
It defines the linearity limit of a receiver or amplifier; beyond this point, nonlinearities create distortion.
A higher IP3 indicates better linearity and less distortion at high signal levels, which are crucial for maintaining signal integrity in crowded or high-signal environments.
Importance of high IP3 in Radio Receivers
Receivers with high IP3 are better at handling strong signals from nearby transmitters or multiple signals simultaneously without generating spurious signals.
This reduces false readings or signal interference, which is critical in applications such as amateur radio, communications, and radar.
Noise, Noise Everywhere
Noise sets the absolute bottom limit of what we can hear. Al divided it into two broad categories:
Natural Noise (QRN)
Galactic background
Atmospheric static
Lightning
Lightning bursts are wideband, energetic, and brutal—but noise blankers can help.
Man-Made Noise (QRM)
This is the stuff we fight all the time:
LED lightbulbs
Switching power supplies
Thermostats
EV chargers
Solar inverters
Grow lights (ask any ham living next to a basement gardener…)
Al even mentioned Chinese HF radar systems—those rapid-fire pulses that light up the waterfall like a machine gun. We can’t fix those, but we can recognize them.
The only real cure for local noise? Track it down and eliminate it at the source. A portable receiver is your best friend here.
A Beautiful Example: The Humble Crystal Radio
Al finished with a walk-through of the simplest possible receiver: the classic crystal set like the one I built as a kid. No power supply. No amplifier. Just:
A resonant LC circuit
A diode detector (originally galena with a cat-whisker)
High-impedance headphones
Crystal radio wiring pictorial based on Figure 33 in Gernsback’s 1922 book “Radio For All” — JA.Davidson at the English Wikipedia, CC BY-SA 3.0, via Wikimedia CommonsCrystal radio schematic. [4]
The entire audio output is derived from the energy in the received RF signal. That still blows my mind—especially knowing how much we depend on active devices today.
Crystal sets are a reminder that, at its core, radio is elegant physics. Everything else—DSP, PLL synthesizers, roofing filters—is refinement.
Final Thoughts
Every chapter in this course has filled gaps in my understanding, but this one tied everything together: noise, filters, amplifiers, mixers, all working in a carefully balanced dance. And as someone who spent a good chunk of the ’80s elbow-deep in analog circuits, it’s incredibly satisfying to revisit the fundamentals with fresh eyes.
Next week, we move into transmitter architecture. I’m looking forward to it—and I’m already expecting another “aha!” moment.
References
[1] A. Penney, Radio Receivers (RAC Basic Course – Chapter 14), Radio Amateurs of Canada, 2025.
[2] A. Z. Peebles, Communication System Principles, 4th ed. Reading, MA: Addison-Wesley, 1998.
[3] American Radio Relay League (ARRL), The ARRL Handbook for Radio Communications, 100th ed. Newington, CT: ARRL, 2023.
[4] B. Finio, ‘Build Your Own Crystal Radio’, Science Buddies. Accessed: Nov. 18, 2025. [Online]. Available: https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p014/electricity-electronics/crystal-radio
From Sparks to Sidebands: Learning Modulation All Over Again
By Doug Nix, VE3— (future call sign pending!)
When I started my electronics career at GFC Hammond Electronics in Guelph back in 1985, I spent my days testing and repairing linear and switch-mode power supplies. At the time, “modulation” meant watching ripple currents on the Tektronix scope or chasing a dead short upstream from an LM723 regulator. It wasn’t until I recently delved deeper into amateur radio that I began to appreciate how the same fundamental principles—mixing, switching, filtering, duty cycles, and harmonics—show up everywhere in RF.
Last night’s RAC Basic lecture from Al Penney was another reminder that nearly every radio mode we use today is built on deceptively simple physical principles: change some characteristic of a carrier, and you can transport information across the planet. What changes is the cleverness with which we do it.
This post is my attempt to capture what I learned, in my own words, with enough technical depth to keep it interesting.
Continuous Wave (CW): Where Radio Began
The earliest radio systems didn’t carry voice—they simply turned a carrier on and off. That’s continuous wave (CW), and it’s astonishingly robust, even in 2025.
CW transmitter block diagram
CW works because the information rate is slow and the bandwidth is tiny. That allows the receiver to use extremely narrow filters—sometimes only a few hundred hertz—which dramatically raises the signal-to-noise ratio. A CW signal can hide below the noise floor and still be copyable by a trained ear.
Keyed sinusoidal waveform, like you might see from a CW transmitter
One technical detail I found particularly interesting: the bandwidth of a keyed carrier is governed by the abruptness of the transitions. “Abruptness” refers to the slew rate of the switching waveform. More abrupt changes require a faster slew rate, which in turn creates harmonics. Slowing the corners on the waveform “softens” the transitions, thereby reducing or eliminating the harmonics.
Hard keying produces broadband splatter due to the harmonics caused by the corners on the waveform—what old-timers call key clicks. So modern rigs shape those edges digitally to keep the spectrum clean.
AM: The First Voice Mode—and the Inefficient One
Amplitude Modulation was the first way we got voice on the air. It is also, by every modern measure, terribly inefficient.
Why?
Because an AM signal consists of:
A carrier (which carries no information)
A lower sideband
An upper sideband
If your audio contains frequencies up to 6 kHz, the RF bandwidth becomes ±6 kHz on each side of the carrier—12 kHz total. Only the sidebands contain information; the carrier exists solely to help a simple diode demodulator recover the audio.
This is why:
AM transmitters waste power on the carrier
AM takes up twice the necessary bandwidth
AM is inherently vulnerable to noise (almost all noise sources are amplitude-based)
PEP (peak envelope power) becomes especially important in AM. A 100 W PEP transceiver can legally deliver only ~25 W of AM carrier because 100% modulation requires the envelope to swing to 4× the carrier power.
Modulated waveform
As someone who spent years debugging over-stressed power supplies, I now appreciate how much engineering went into keeping broadcast transmitters from exceeding that 100% limit. Overmodulation introduces phase reversals and spurious emissions extending theoretically to infinity—an EMC/Spectrum nightmare.
Mixers: The Beating Heart of RF
Al’s explanation of mixing echoed something I first learned at Hammond while troubleshooting transformers: non-linear systems create new frequencies.
A mixer multiplies two signals:
Carrier frequency f1
Modulating or local oscillator frequency f2
The output contains:
f1 + f2
f1 – f2
…plus other products if the device is imperfect, which it always is.
This simple principle is what makes the superheterodyne receiver possible, and it’s how we shift an audio waveform up into the RF spectrum. Every mode—AM, FM, SSB, digital—depends on this idea.
Sidebands and SSB: Why We Don’t Run AM Anymore
In amplitude modulation, all the information is in the sidebands. Once you realize that both sidebands contain the same information, it becomes obvious: send only one.
Enter Single Sideband (SSB)—a refinement of AM where:
One sideband is removed
The carrier is suppressed
Bandwidth is cut in half
Transmitted power is concentrated entirely in the useful spectrum
That’s why SSB is the standard for HF voice. With a typical 3 kHz voice channel:
AM occupies ~6 kHz
SSB occupies ~2.7–3.0 kHz
FM occupies 10–15 kHz
And you can fit 2× as many SSB QSOs into a band as AM
SSB also gives far better “punch” for the watt. A 100 W PEP SSB signal delivers voice peaks that punch through marginal conditions, and your average power is typically 10–20% of that unless you engage heavy speech processing [1].
FM: Quieting, Capture, and Why VHF Sounds So Clean
Frequency Modulation is a different animal. Instead of changing amplitude, we change the instantaneous frequency of the carrier.
Two things make FM special:
1. It rejects amplitude noise
Because the information is in the frequency deviation, not amplitude, the receiver can use a limiter to discard all amplitude variation. That’s why FM broadcast radio sounds clean even with multipath, ignition noise, and urban interference.
2. The Capture Effect
If two FM signals are present on the same frequency, the stronger one “captures” the receiver. This is both a blessing (for repeaters) and a curse (for aviation, which uses AM, allowing overlapping transmissions to still be heard).
FM also supports wideband (e.g., ±75 kHz for broadcast) and narrowband (typically ±2.5–5 kHz for amateur VHF/UHF).
Carson’s Rule gives a quick estimate of FM bandwidth:
BW ≈ 2 (Δf + fm) where Δf is peak deviation and fm is highest audio frequency.
So a typical VHF ham radio:
±3 kHz deviation
3 kHz audio
BW ≈ 12 kHz
No wonder we must be careful about over-deviating—your excitement literally widens your signal.
Digital Modes: RTTY, Packet, and the March Toward Software
Watching Al trace the evolution from Baudot, to AFSK, to modern sound-card decoding reminded me how far we’ve come from electromechanical teleprinters banging away in newsrooms.
RTTY uses frequency shift keying (FSK):
One frequency = mark
Another = space
Typically ~170 Hz shift on HF
Packet radio took the next step by wrapping data into structured frames with error detection (FCS) and acknowledgments—essentially, an early version of TCP/IP over RF.
Today, software like fldigi, WSJT-X, and Direwolf replaces dozens of kilograms of mechanical equipment with a laptop and a USB cable.
It’s astonishing to think that in my Hammond days, many of these digital modes were still hardware-based. Today, everything from modulation to filtering to demodulation is done numerically.
Reflections as a New(er) Ham
Studying modulation theory now—at this stage of my life—is a strange kind of homecoming. It’s refreshing, frankly. I’m reconnecting with the core physics and mathematics that first drew me into electronics before life led me into safety engineering, risk assessment, standards development, and consulting work.
What strikes me most is that every mode is a tradeoff:
AM: simple but inefficient
SSB: efficient but harder to generate and tune
FM: noise-resistant but spectrally wide
CW: narrow and penetrating but slow
Digital: flexible but computationally heavy
Each choice reflects a balance between bandwidth, power, complexity, and robustness—the same constraints I deal with every day in engineering safety systems.
And that’s the joy of amateur radio: it’s the perfect intersection of physics, engineering, history, and pure hands-on experimentation.
Can’t wait for the next chapter!
References
[1] A. Penney, Chapter 13 – Modulation and Transmitters. RAC Basic Qualification Course, Radio Amateurs of Canada. Ch13-Modulation-and-Transmitters
[2] W. Sabin and E. Schoenike, HF Radio Systems & Circuits. New York, NY, USA: McGraw-Hill, 1998.
[3] J. R. Carson, “Notes on the Theory of Modulation,” Proceedings of the IRE, vol. 10, no. 1, pp. 57–64, Feb. 1922.
[4] E. H. Armstrong, “A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation,” U.S. Patent 1,941,066, filed Dec. 26, 1933, and issued Dec. 26, 1933.
[5] Federal Communications Commission (FCC), Title 47 CFR Part 97 – Amateur Radio Service, U.S. Government Publishing Office, 2024.
[6] A. B. Carlson, Communication Systems: An Introduction to Signals and Noise in Electrical Communication, 4th ed. New York, NY, USA: McGraw-Hill, 2002.
[7] J. D. Kraus, Electromagnetics, 4th ed. New York, NY, USA: McGraw-Hill, 1992.
[8] G. L. Tarkington and R. L. Ferrel, “The Single-Sideband Story,” QST, vol. 41, no. 7, pp. 17–23, July 1957.
[9] M. Schwartz, W. R. Bennett, and S. Stein, Communication Systems and Techniques. New York, NY, USA: McGraw-Hill, 1966.
[10] H. T. Friis and C. B. Feldman, “A Multiple-Unit Steerable Antenna for Short-Wave Radio Transmission,” Bell System Technical Journal, vol. 17, no. 2, pp. 337–364, Apr. 1938.
[11] K. R. Hardis, “Understanding Peak Envelope Power,” QEX – Communications Quarterly, no. 169, pp. 3–10, Nov./Dec. 1995.
[12] ITU Radiocommunication Bureau, ITU-R SM.328-12: Spectra and Bandwidth of Emissions, International Telecommunication Union, Geneva, 2015.
[13] ITU Radiocommunication Bureau, ITU-R F.1110 – Frequency-Shift Keying and Keying Characteristics, International Telecommunication Union, Geneva, 2019.
[14] L. E. Kahn, “Single-Sideband Transmission by Envelope Elimination and Restoration,” Proceedings of the IRE, vol. 40, no. 7, pp. 803–806, July 1952.
[15] D. H. Johnson and J. E. Johnson, Modern Communications Systems: Principles and Applications. Boston, MA, USA: Pearson, 2010.
Getting on the Air: Lessons from Chapter 12 of the RAC Basic Certificate Course
When you’re working toward your amateur radio certification, there’s a lot of theory to digest — regulations, electronics, antennas, propagation. But for most of us, the real excitement begins when we start to imagine what it’ll be like actually to get on the air. Al Penney’s Chapter 12 in the RAC Basic Certificate Course bridges that gap beautifully, showing how all the groundwork—resistors, Ohm’s law, decibels, and dBμV—comes together when you finally sit down at the radio, call sign in hand, and start operating for real. It’s a chapter that shifts the focus from knowing to doing.
From Q-Codes to Phonetics: Speaking the Language of Radio
One of the earliest surprises for many new hams is just how structured on-air communication really is. Penney revisits the history of the Q-codes, developed around 1909 to help ships communicate across language barriers. Codes like QRP (“reduce power”) or QTH (“location”) remain in use today—succinct, efficient, and a reminder that brevity is part of good operating [1]. Having said that, Q-codes have been one of the big challenges for me. As a systems thinker, I look for internal logic in coding systems. Unfortunately, there isn’t an internal system for Q-codes, except at the highest level. Anyway, I’ll start with the most important ones, and if there are more that I need, I’m sure I’ll learn them as I need them 🤷♂️.
Equally important is the phonetic alphabet, the backbone of clear voice communication. Whether you’re spelling out your call sign or confirming a grid locator, “Whiskey Delta Nine Tango Echo” is a lot clearer than “W-D-9-T-E” over a noisy channel. The modern NATO/ICAO phonetic alphabet, with words like Alfa, Bravo, and Juliett, dates to 1956 and remains standardized across aviation, maritime, and amateur services.
NATO/ICAO Phonetic Alphabet
And then there are the many on-air abbreviations used when communicating by Morse Code on CW (just a few):
AR End of message
AS Wait
BK Break
BT Separator
K Over
KN Over (to specific station)
SK End of contact
etc.
Then there’s HF, with SSB depending on the band and mode of communication, as well as digital modes such as Automatic Packet Reporting System (APRS), Amateur Teleprinting Over Radio (AMTOR), Phase Shift Keying, 31 Baud (PSK31), and others.
It’s a lot. This is an elephant I need to eat a bite at a time.
The Repeater: Your Gateway to the Airwaves
For most beginners, the first contact happens through a repeater—that wonderful piece of infrastructure that listens on one frequency and simultaneously transmits your signal on another. These are full-duplex systems, often perched high on towers or mountain tops, dramatically extending your range beyond what a handheld or mobile rig could achieve on its own.
How communication with a radio repeater works
Each repeater pair operates with a standard offset—typically 600 kHz on the 2 m band—and may require a PL (CTCSS) tone to access. If your local machine needs a 136.5 Hz tone and you forget to program it, you’ll be talking to yourself! These tones prevent repeaters from keying up in response to stray interference and are crucial in maintaining a civil and usable spectrum.
On the Air: First QSOs and Good Etiquette
Penney devotes an entire section to that moment every new ham remembers—the first QSO. The key takeaway? Listen first. Nothing will endear you faster to your local club than showing patience and situational awareness before you key up. Once you do, identify clearly, use your call sign at the start and end of each contact, and every 30 minutes in between. Never “kerchunk” the repeater (key up without identifying) just to test your signal—that’s poor form and, technically, illegal.
Al’s guidance on etiquette reads like a master class in radio citizenship. Give others a chance to use the repeater, keep conversations courteous and on-topic, and remember that repeaters are shared resources. Even small gestures—like helping maintain the repeater site or simply donating a few dollars to the local club—go a long way toward keeping our networks alive.
HF Operating: Beyond the Repeater
If VHF and UHF are your local playgrounds, HF is where you discover the world. Penney’s treatment of HF operation in this chapter demystifies what can seem like chaos: no channels, variable signal strength, fading (QSB), and the ever-present QRN of static. The key difference is that HF communication relies on the ionosphere, where refraction allows signals to bend around the globe—but also fade, flutter, and overlap in unpredictable ways.
SSB operation (upper sideband above 30 m, lower sideband below) dominates HF phone communication for its bandwidth efficiency—roughly 3 kHz compared to FM’s 15–20 kHz. Combine that with proper filtering, good receiver selectivity, and a healthy dose of patience, and suddenly you’re working stations thousands of kilometres away with only a hundred watts and a length of wire in the trees.
The Spirit of Amateur Radio
Perhaps the most valuable insight from this chapter isn’t technical at all—it’s cultural. Whether through repeaters, satellites, or CW on a quiet 40-meter band, amateur radio is as much about how we operate as it is about what we operate. Penney closes with a reminder that respect, curiosity, and generosity are the invisible glue that keeps this community together. Every “73” sent across the airwaves carries a little of that tradition forward.
References
[1] A. Penney, RAC Basic Certificate Course: Chapter 12 – Operating a Station, Radio Amateurs of Canada, 2024. [2] “NATO Phonetic Alphabet,” Wikipedia, https://en.wikipedia.org/wiki/NATO_phonetic_alphabet. [3] “IRLP and EchoLink,” Amateur Radio Wiki, 2023. [4] “Ham Radio 101: Digital Signal Processing,” HamRadioSchool.com, 2023.
My business card at GFC prior to the spin-off of the organization in 1989
From Hammond to High Efficiency: Reflections on Power Supplies Then and Now
In 1985, when I started my career at GFC Hammond Electronics in Guelph, Ontario, the hum of transformers and the scent of flux were part of my daily environment. As a production test technician, my job was to test and repair linear and switching power supplies—work that gave me an intuitive feel for what really makes electronic systems tick.
1989 – L-R: Bruce Ritchie (QA Manager), me, a Korean colleague, and Jerry Williamson (Manufacturing Engineering) in front of the Curtis Road plant in 1989.
The Hammond facility on Curtis Road was a fascinating place for someone just starting out in electronics. The Hammond Museum of Radio was located in the same building, and the local amateur radio club’s repeater, VE3HC, had a tower at the back of the plant. Fred Hammond himself—whose name is etched into Canadian radio history—could often be found tinkering or chatting with staff. For a young technician like me, those were inspiring encounters that linked the practical side of my work to a century of radio innovation.
Understanding the Foundations
To appreciate modern power supplies, it helps to look back to the origins of the electrical grid itself. The way we generate and distribute electricity has always shaped the way we convert it.
Thomas Edison, 1922George Westinghouse Jr., 1884Nikola Tesla about 1890
In the late 19th century, the “War of the Currents” pitted two of the era’s greatest inventors against each other: Thomas Edison, who favoured direct current (DC), and Nikola Tesla, whose alternating current (AC) system was backed by George Westinghouse. Edison’s DC approach had the advantage of simplicity and safety, but it couldn’t transmit power efficiently over long distances. Tesla’s AC system, on the other hand, used transformers to step voltage up for transmission and down for use—making large-scale distribution practical for the first time.
The debate was settled decisively in 1895, when the Niagara Falls hydroelectric plant—built by Westinghouse—demonstrated the superiority of AC power. The plant’s generators produced 25 Hz alternating current, a frequency chosen as a compromise between efficient motor operation and adequate lighting performance. While 25 Hz served early heavy industry well, it wasn’t ideal for all applications. By the early 20th century, 60 Hz had become North America’s standard, striking a balance between efficiency and performance for the emerging electrical grid. [2]
Across the Atlantic, Europe standardized on 50 Hz, largely through the influence of engineers at AEG and the VDE. They determined that 50 Hz offered the best trade-off between voltage drop, lighting flicker, and motor design. The choice was also elegantly compatible with the metric system—a detail the Germans took no small satisfaction in noting. [1]
These early engineering decisions still echo in our wall sockets today. The world’s grids may differ by frequency and voltage, but they all deliver alternating current—a form of power distribution optimized for transmission, not for the needs of modern electronics.
Why Electronics Need Conversion
For electronic systems, line-frequency AC power isn’t directly useful. Radios, computers, and control circuits all require direct current (DC)—and not just any DC, but clean, stable, and precisely regulated voltage. This is where power converters come in: they transform AC into DC and sometimes back into AC at different frequencies for specialized uses, such as motor drives or RF systems.
This need for efficient and reliable power conversion drives the evolution from linear to switch-mode power supplies—the very technologies I worked on daily at Hammond.
Linear Power Supplies
In a traditional linear power supply, the transformer does the heavy lifting, stepping up or down the voltage and isolating the circuit from the mains. The rectifier converts AC to DC—first through simple half- or full-wave circuits and later through the now-ubiquitous bridge rectifier. The resulting pulsating DC is smoothed by large electrolytic capacitors, which store charge between cycles to reduce ripple.
Filtering and regulation define the character of a linear supply. Early designs used Zener diodes or discrete transistor regulators, which three-terminal IC regulators, such as the LM78xx series later replaced. Linear regulators operate in the transistor’s linear region, dropping excess voltage as heat—a simple, reliable, and noisy (in the thermal sense) way to achieve a stable output.
Linear supplies have an unmistakable presence: heavy transformers, warm chassis, and that faint 120-Hz hum that signalled a tired filter capacitor. They were dependable, repairable, and forgiving—a good match for the analog age.
A Vacuum tube rectified DC power supply for a tube amplifier. The B+ voltage has the same function as Vcc in semiconductor circuits.
Because linear supplies operate in the linear region of the transistors, the difference between the raw rectified DC and the output voltage must be dropped across the regulator transistor(s), resulting in significant I2R losses in those devices. [4], [5].
Linear 5 Vdc regulated power supply. The rating of the LM7805 regulator limits the output current from this design. [4]
From Linear to Switching
By the time I arrived at Hammond, switch-mode power supplies (SMPS) were reshaping the field. Instead of relying on bulky transformers at 60 Hz, SMPS designs rectify the AC first, then chop the DC at high frequency—tens or hundreds of kilohertz—using transistors operating in saturation (fully on or off). The high frequency allows much smaller transformers and capacitors, dramatically improving efficiency and reducing weight.
Of course, early SMPS units had their quirks. Without proper filtering—MOVs, chokes, and capacitors on the input—they could fill an HF receiver’s spectrum with a wash of interference. However, as designs matured, improved EMI filters, shielding, and power factor correction made switching supplies both quieter and more efficient.
How switching power supplies work
In switch-mode supplies, the AC mains power is first rectified. Then, the DC power is converted back to AC at a much higher frequency, allowing smaller, lighter, and less expensive transformers to be used to provide the lower AC voltages needed for the load(s). The use of higher frequencies also means that the filter capacitors can be smaller in size and lighter in weight. Additional inductors are required to prevent high-frequency switching noise from transferring to the load side of the supply. The benefit is that the primary power converter can use pulse-width modulation, keeping the switching transistors operating in their saturation mode, and thereby reducing the I2R losses in the transistors that result in waste heat. [6], [7].
What’s easy to forget is that early SMPS units were not always well-behaved neighbours in a radio shack. Without proper transient filtering—MOVs, chokes, and capacitors on the input—they could turn the HF spectrum into a wash of hash. Today’s designs, with improved EMI filtering and power factor correction, are worlds better.
Lessons That Endure
Looking back, my time at Hammond laid a foundation for everything that followed. Power supplies are not just supporting components; they’re the heart of every electronic system. If the supply isn’t clean, stable, and appropriately rated, nothing downstream behaves as intended.
Al Penney’s excellent presentation [3] on power supplies for amateur radio operators captures that same truth: whether you’re winding transformers, testing LM7805 regulators, or designing 90%-efficient SMPS circuits, the goal remains constant—reliable, safe power delivery.
For me, that journey began on a test bench in Guelph, soldering iron in one hand and scope probe in the other—under the same roof where Fred Hammond preserved the history of radio. It’s a fitting reminder that every modern innovation, no matter how advanced, still rests on a well-built power supply.
References
[1] G. Neidhöfer, ‘50-Hz Frequency [History]’, IEEE Power and Energy Mag., vol. 9, no. 4, pp. 66–81, July 2011, doi: 10.1109/MPE.2011.941165.
[2] P. Mixon, ‘Technical origins of 60 Hz as the standard AC frequency in North America’, IEEE Power Eng. Rev., vol. 19, no. 3, pp. 35–37, Mar. 1999, doi: 10.1109/MPER.1999.1036103.
[3] A. Penney, Power Supplies, VO1NO, RAC Basic Amateur Radio Course, 2023.
[4] O. M. Urias, ‘How to Build a DC Linear Power Supply’, Build Electronic Circuits. Accessed: Oct. 30, 2025. [Online]. Available: https://www.build-electronic-circuits.com/linear-power-supply/
[7] C. Atwell, ‘A Brief History of Switching Power Supplies’, Electronic Design. Accessed: Nov. 07, 2025. [Online]. Available: https://www.electronicdesign.com/technologies/power/article/55040799/electronic-design-switching-power-supply-history-from-theory-to-design-essential
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