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 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.

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.

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 + f_m)
where Δf is peak deviation and f_m 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.

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.

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.

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.

From Vacuum Tubes to Transistors: A Personal Reflection on the Building Blocks of Modern Electronics

Every once in a while, I come across a presentation that reminds me just how remarkable our journey in electronics has been. Al Penney’s “Diodes, Transistors and Tubes”, class 9 in the RAC Basic Qualification Course, is one of those — a concise, clear walk-through the history and physics that underpin virtually everything we take for granted in modern technology. [1]

For anyone who’s ever built a circuit, troubleshot a control system, or simply wondered how a radio turns electromagnetic waves into sound, Al’s lecture is a reminder that the devices we use daily rest on a few elegant physical principles.

Atoms, Electrons, and the Dance of Conductivity

Al starts where all good electronics stories should: the atom. Protons, neutrons, and electrons — familiar from high school physics — become the players in a complex dance that determines whether a material is a conductor, an insulator, or something in between.

Semiconductors sit in that fascinating “in-between” zone. By carefully introducing impurities, or doping, engineers can coax silicon or germanium into behaving predictably — letting electrons move when we want them to and stopping them when we don’t. That’s the foundation of everything from radio detectors to modern CPUs.

The Simple Genius of the Diode

The humble semiconductor diode, as Al explains, is just a P–N junction that lets current flow one way but not the other.

It’s the electronic equivalent of a check valve — elegantly simple, profoundly useful. With that one device, we can rectify AC into DC, demodulate radio signals, or stabilize voltage with a Zener diode.

I’ve always appreciated how intuitively physical these analogies are. Whether you think of diodes as electrical check valves or semiconductors as engineered crystals, they connect the abstract world of physics with the very real world of current and voltage.

Transistors: The Revolution in a Grain of Germanium

Then came the transistor — arguably the most transformative invention of the twentieth century. Al’s slides capture both the historical significance and the practical brilliance of that moment in 1947 when Bardeen and Brattain’s point-contact transistor first amplified a signal.

Before that, we relied on vacuum tubes: glowing, fragile, power-hungry devices that filled radio chassis and computer rooms.

The transistor changed everything. It was small, efficient, rugged — and as Al notes, it enabled everything from portable radios to the computers that now run our world.

As someone who’s spent a career around control systems and functional safety, I find the transistor’s evolution from that sliver of germanium to today’s silicon MOSFETs a story of both science and engineering perseverance. Billions of transistors now sit on a chip smaller than your fingernail — each one still following the same basic principles first demonstrated in a Bell Labs lab bench.

Amplifiers and the Art of Control

One of Al’s most practical sections deals with amplification.

Whether we’re talking about boosting a microphone signal, driving a loudspeaker, or switching a safety relay, the amplifier’s purpose is the same — to make a small signal powerful enough to do useful work.

Transistors and FETs handle this task differently, but the core idea is universal: use a small input to control a larger output. In machinery safety and control, this principle is evident everywhere — from sensor conditioning to PLC inputs and output stages, as well as pneumatics and hydraulics.

Reflections on a Legacy of Innovation

Al’s presentation closes with a nod to vacuum tubes — those glowing ancestors of the solid-state devices we know today. While they’ve been mostly replaced, they still hold a special place in audio and RF engineering for their distinctive performance characteristics.

Vacuum tubes are still commonly used in specialized radio applications, particularly in high-power RF transmitters, including commercial radio and television broadcasting, amateur radio, and military communication systems. Their ability to handle high voltages, high power levels, and their linear amplification characteristics make them preferred in these settings where solid-state devices may be less reliable or unable to perform as well. Vacuum tubes are also valued for their durability in harsh environments, such as those with radiation or electromagnetic pulses (EMP), which is particularly important for military and aerospace applications.

Key Radio Applications of Vacuum Tubes Today

• High-Power Radio Transmitters: Commercial broadcast stations still use vacuum tubes for final power amplification due to their capacity to handle large RF power loads.
• Amateur Radio Equipment: Many ham radio operators prefer tube-based transmitters for their superior signal handling, natural overload tolerance, and call sign authenticity in traditional equipment.
• Military Communications: Vacuum tubes are preferred in certain military radios because of their robustness against EMP and radiation, ensuring reliable operation under extreme conditions.
• Specialized Scientific and Industrial RF Systems: Vacuum tubes are used in some radar, industrial RF heating, and scientific instruments requiring high voltage and power.

Additional Contemporary Uses Related to Radio

• Vacuum tubes find niche roles in audio amplification equipment connected to radio receivers due to their characteristic sound.
• Vacuum tube audiophile amplifiers are increasingly common, where their soft roll off when over-driven yield a much better sound than the harsh clipping that transistors give under similar conditions.
• Some hybrid designs combine vacuum tube stages with solid-state components in modern radio equipment.

Thus, while transistors have largely replaced vacuum tubes in most consumer electronics, vacuum tubes remain essential in applications where their unique electrical and physical properties provide advantages that solid-state devices cannot fully match [5][6][7][8].

Reading through this material reminded me that understanding where our technology comes from isn’t just nostalgic — it’s essential. Whether we’re designing safety systems, writing standards, or just tinkering in the shop, the principles that Al Penney lays out are as relevant today as they were when the first transistor clicked into life.

In short: the story of diodes, transistors, and tubes isn’t just about components — it’s about curiosity, experimentation, and the human drive to control and harness electricity.

Thanks, Al Penney (VO1NO), for reminding us how far we’ve come — and how much of that journey is still worth exploring.

Bibliography

[1] A. Penney, ‘Chapter 9 – Diodes, Transistors, and Tubes’, Radio Amateurs of Canada, Canada, Nov. 02, 2025. Accessed: Nov. 02, 2025. [Online]. Available: https://www.rac.ca/

[2] J. T. Rubin, ‘The Invention of the Transistor’. Accessed: Oct. 29, 2025. [Online]. Available: https://www.juliantrubin.com/bigten/transistorexperiments.html

[3] ‘Vintage 1940s Operadio Tube Amplifier Guitar Lap Steel Amp 5641 Speaker’, Worthpoint.com. Accessed: Nov. 01, 2025. [Online]. Available: https://www.worthpoint.com/worthopedia/vintage-1940s-operadio-tube-amplifier-4596304184

[4] A. Singh, ‘Types of Transistors: Classification (BJT, JFET, MOSFET & IGBT)’, Hackatronic. Accessed: Nov. 01, 2025. [Online]. Available: https://www.hackatronic.com/types-of-transistors-classification-bjt-jfet-mosfet-igbt/

[5] Vacuum Tubes: Complete Guide to Types, Applications & … https://www.blikai.com/blog/vacuumtube/vacuum-tubes-complete-guide-to-types-applications-modern-roles

[6] Are Vacuum Tubes Still Used (& What Are They Used for)? https://pentalabs.com/blogs/tube-talk/are-vacuum-tubes-still-used

[7] When Old is Gold: Harnessing the Power of Vintage … https://www.radiodesigngroup.com/blog/when-old-is-gold-harnessing-the-power-of-vintage-technology-for-modern-applications

[8] Vacuum Tube Market Size & Share 2025-2032 https://www.360iresearch.com/library/intelligence/vacuum-tube

[9] Brief Overview of Vacuum Tubes and Circuits https://www.bristolwatch.com/science/vacuum_tubes.htm

[10] Vacuum tubes and modern uses for them : r/ECE https://www.reddit.com/r/ECE/comments/4hmi03/vacuum_tubes_and_modern_uses_for_them/

[11] List of vacuum tubes https://en.wikipedia.org/wiki/List_of_vacuum_tubes

[12] Modern Radio Technology Comparison to Tube Radio https://www.youtube.com/watch?v=GVXwsdsIyiI

[13] Unlocking the Future of Vacuum Tube: Growth and Trends … https://www.marketreportanalytics.com/reports/vacuum-tube-376095

[14] H. W. Silver, ‘Vacuum Tubes’, Nuts and Volts Magazine, no. November, pp. 8–11, 2017. Accessed: Nov. 01, 2025. [Online]. Available: https://www.nutsvolts.com/magazine/article/vacuum-tubes

[15] ‘Oilily A88 Vacuum Tube Integrated Amplifier, 45W+45W Class AB, EL34/KT88 Tube Amplifier with Triode & Ultra-Linear Mode, External Bias Adjustment, High-Fidelity Sound for Audiophiles (Black)’, Tube Amplifier Reviews. Accessed: Nov. 01, 2025. [Online]. Available: https://tubeamplifierreviews.com/oilily-a88-vacuum-tube-integrated-amplifier-45w45w-class-ab-el34-kt88-tube-amplifier-with-triode-ultra-linear-mode-external-bias-adjustment-high-fidelity-sound-for-audiophiles-black/