If you hear"Software-Defined Radio (SDR)"Five characters; first reaction is"Hardcore, distant, and irrelevant to me"——This book is written for you.
This time, Alice sets off again. What she’s going to show you is the communication capability.How to be re-implemented in softwareHow functions originally hardwired into hardware are redefined, line by line, through code.
Thus, this book—*Alice’s Adventures in the Software-Defined Radio (SDR) World*—was born.——An event that"Software-Defined Radio (SDR)"A science-popularization journey infused with fantasy and adventure.
🌟 One-sentence core theme
In the old world, communication equipment was like isolated islands.The Soldered CastleEach room has its own designated function—immutable and immovable. In contrast, Software-Defined Radio (SDR) transforms these isolated rooms into a single, integrated facility.Can be disassembled and reassembled using building blocks.the castle——The same hardware can be a radio today, a radar tomorrow, and a device you haven’t even imagined yet the day after.
This is what this book truly aims to clarify: when"Software becomes the soul."How will the world of communications change?
🗺️ Complete Book Map (13 Stations)
- Opening | Falling into the “Reconfigurable” Rabbit HoleAlice opens “Principles of Communication” and steps into the Software-Defined Radio (SDR) rabbit hole.
- Chapter 1 | The Hardware CageIn the old world, those soldered-in, unmodifiable devices were like sealed rooms.
- Chapter 2 | The Manifesto of Software: Code cascades like a waterfall,"A/D As close to the antenna as possible"——Software begins to take over everything.
- Chapter III | The Body of SDRFrom antenna to digital, and back from digital to antenna—a complete blueprint of the signal’s journey.
- Chapter IV | The Stage of the Three Brothers：FPGA、DSP、CPU How to divide responsibilities and collaborate on the same board.
- Chapter 5 | Digital Frequency Conversion Factory：DDC / DUC How to change the frequency"Translate"Come"Translate"Go.
- Chapter 6 | Hardware ExpoFrom tens of yuan to over one hundred thousand yuan—see a wide variety of boards all at once.
- Chapter 7 | Building-Block CastleSignal processing is decomposed into draggable and reconfigurable components."Building Blocks"Module.
- Chapter 8 | First ProjectFollow Alice to build your first SDR system using flowgraphs. FM Radio.
- Chapter 9 | Radar, Radio Astronomy, and Cognitive SystemsHow can the same board assume four completely distinct identities?
- Chapter 10 | From Professional to CivilianHow Software-Defined Radio (SDR) Evolved from a Mysterious Specialized Field into Laboratories and Studios
- Chapter 11 | Kaleidoscope: One board, infinite possibilities——The Imagined Boundaries of Software-Defined Radio (SDR)
- Ending | Returning to the RiversideWhen software becomes the soul, the world of communications changes.
👥 Who Is This For?
- Want to understand Software-Defined Radio (SDR), but intimidated by the formulas?Beginner readers
- Communication / Electronics / Automation-related majorsStudent
- Want to get hands-on with hardware boards and work on projectsEngineers and Enthusiasts
- and——All still remember."Alice Chasing the Rabbit"ofThe Curious Person
📖 How do you read this?
It is recommended to read from the beginning to the end, following Alice’s footsteps. The book covers RF front-ends, analog-to-digital conversion,FPGAdigital frequency conversion, hardware selection, and flowgraph programming"Hard terms"are all woven into the story. If you encounter unfamiliar concepts, don’t panic—just keep reading; the story itself will tie them together for you.
Today, we begin with the “Preface.”
And with Alice, fall into that…"Reconfigurable"the confessional.
Opening | Falling into the “Reconfigurable” Rabbit Hole
It has been three weeks since Alice returned from her first adventure.
She never chased rabbits again—not because she had become more mature.——but because she had found something more interesting than chasing rabbits: she began carefully reading her sister’s textbook, *Principles of Communications*.
Those formulas and block diagrams that once made her drowsy now appeared entirely different to her. When she saw them on the pages of her textbook…“Modulation”When it’s two characters, a carousel appears before one’s eyes.AMthe ups and downs; witnessing“Encoding”At that moment, the whisper from the smoke ring exhaled by the Coding Worm echoed in my ears; I saw…“Synchronization”At that moment, the golden, silver, bronze, and iron gleams of the four large clocks on the Bell Tower still shimmered vividly before one’s eyes.
She has already been able to understand half of the content.
But the other half, she couldn’t understand.
Not because she cannot understand the formulas——but rather because she encountered a puzzling question in the book:
“Every function described in this book is implemented using dedicated hardware circuits.”
She flipped the book to the chapter on AM radios, where a detector circuit composed of diodes, capacitors, and inductors was illustrated.“Once the hardware is soldered, it can only perform this specific task.”She then turned to the chapter on FM radio, where the circuit was entirely different.“Changing a function requires replacing the entire hardware set.”
She flipped to the chapter on radar again.“A radar’s circuitry is one hundred times more complex than that of a radio.”Turn over again.Wi-FiThat chapter.“Yet another completely different circuit.”
Alice closed the book and stared blankly at its cover for a long time.
“Why can’t there be a universal one?‘Universal Printed Circuit Board’，”She murmured to herself.“Install radio software, and it becomes a radio; install radar software, and it becomes a radar; install…Wi-FiThe software isWi-Fi? Just like……Just like wearing different clothes transforms me into a different person?”
She waited for the white rabbit to appear.
The White Rabbit did not come.
She waited the entire afternoon, ate three cookies, drank a cup of tea, and looked out the window twenty-six times.——The White Rabbit never appeared.
“It seems the first incident was just an accident.”Alice sighed and placed the book on the nightstand, preparing to sleep.
She blew out the candle.
In the darkness, a voice rang out—not coming from outside the window, nor seeping in through the door crack.——but rather a sound emanating from between the pages—like something long suppressed, finally finding an outlet:
“You’re right. Why not?”
Alice sat up abruptly and relit the candle.
That book is co-authored. Yet a sliver of light shines through the gap between its pages.——Not candlelight, but a blue, flowing light—like a stream of signals. That light seeped out from between the pages of the book and coalesced in midair into a line of text:
“Hardware is the body; software is the soul. Why can the body host only one soul?”
Then the book“Snap”with a soft sound, it opened itself. The page it landed on featured an illustration she had never seen before.——Not a circuit diagram, not a waveform diagram, but a diagram.Signal Processing FlowchartColorful building-block modules are connected by arrows and arranged to form a complete signal chain. Adjacent to it on the same page is another diagram: the same building-block modules, rearranged in a completely different configuration, constitute an entirely different system.
Below the two figures, a footnote is written in extremely small font:
“The same hardware, different software—completely different functionalities.”
Alice hadn’t had time to take a closer look when, suddenly, a hurried set of footsteps sounded outside the window.
She pushed open the window.——
aWhite RabbitStanding on the windowsill.
But he was completely different from his first adventure. This time, he wasn’t wearing a waistcoat or carrying a pocket watch. He wore a T-shirt printed with…“GNU Radio”black charactersTXu, holding a palm-sized blue circuit board in his arms——An antenna connector is soldered above.USBInterfaces, various chips, and indicator LEDs are blinking rhythmically, like a tiny heartbeat.
The White Rabbit did not say anything.“It’s too late.”He simply held the circuit board up in front of Alice and said:
“Give it a try. The same hardware board, but different software: install this software—it becomes a radio; install that software—it becomes a spectrum analyzer; switch to another—it becomes a radar.”
“How do I replace it?”Alice asked.
“In code.”The White Rabbit said,“Software-defined: Implementing functionality in code rather than soldering it onto circuitry.”
He turned and leapt out the window into the night.
Alice didn’t hesitate—she snatched the book off the desk, vaulted over the windowsill, and dashed after him. Clutched tightly in her hand was the textbook *Principles of Communication*, and the line of blue text nestled between its pages still faintly glowed.“The same hardware, different software——Completely different functions.”
This time, the tree hollow was not by the riverside; it appeared beneath the fence at the end of the garden.——A place that had never existed before, with neatly trimmed edges, and a small plaque embedded above the entrance, inscribed with three characters:
“Reconfigurable.”
Alice bent down and crawled inside.
Fall.
Just like the first time, this is a bottomless vertical shaft. But this time, sine waves, square waves, and triangular waves are not hanging on the shaft walls.——but rather a series ofDynamic FlowchartColorful building-block modules rapidly scroll along the well wall, rearranging themselves like a zoetrope: the first frame shows a set of blocks assembled into…“FMRadio”Flowgraph; the second frame becomes“Spectrum Analyzer”the flowgraph; the third frame changes again to“Radar Ranging”flowgraph……On the same base, the arrangement of building blocks changes every second, with each arrangement corresponding to a completely different radio function.
Alice reached out to touch one of them.“Low-pass filter”Building Blocks——It looks like a red LEGO brick.——But as soon as her hand reached out, the entire flowchart melted and reassembled into another one.
“Don’t touch it.”A voice came from beside her.“Your flowgraph is running. Touching it will mess everything up.”
Alice turned her head.
The White Rabbit was squatting on a protruding platform on the well wall, with the blue circuit board resting on his knees—the indicator light still blinking. Sitting beside him was a…Cheshire Cat——No, that wasn’t the same cat she’d seen last time. The previous cat’s fur shimmered with a flowing rainbow; this cat’s body, however, was…Semi-transparentYes, like a transparent glass, with blue data streams flowing inside—from the head all the way to the tip of the tail, then cycling back.
“You are……The younger brother of Spectrum Cat?”Alice asked tentatively.
The transparent cat grinned.——Its smile has no teeth—only a string of continuously scrolling code characters flickers at the position of its lips.
“Call meFlowgraph Cat”The cat said,“Spectrum Cat Manager‘How do I check the frequency?’I’m in charge.‘Function’Welcome to——A Software-Defined World.”
Alice continued falling. Below grew increasingly bright, and she saw the silhouette of a massive castle.——No, not a room built of bricks and stones like those in the old world, but rather a structure made of…Countless flowcharts projectedA city composed of such elements. Each building in the city represents an unfolded signal processing flowgraph, and buildings are interconnected via virtual data lines. At any given moment, the entire city executes millions of distinct functions simultaneously—yet its underlying hardware infrastructure remains unchanged.
Her feet touched the ground.
The ground beneath one’s feet is neither soil nor stone.——but rather a boardProgrammable Baseboardlike a giant touchscreen, displaying a line of welcome text:
“This is the world of Software-Defined Radio (SDR). The same hardware platform can wear an infinite number of ‘clothes.’”
Alice looked up.
Before her stood a massive portico, above which an inscription was carved—identical to the blue line of text in her textbook *Principles of Communication*:
“Hardware is the body; software is the soul. The body may remain unchanged, while the soul undergoes endless transformations.”
The White Rabbit was already standing inside the porch, his back turned to her, connecting something with that blue circuit board. The Flowchart Cat crouched on his shoulder, its tail tip flickering with code characters.
“Won’t you come in and take a look?”The White Rabbit said without turning its head,“Haven’t you been asking that question all along?”
“What’s the issue?”Alice asked.
The White Rabbit turned around. All the indicator lights on that circuit board lit up, emitting dazzling brilliance.——
“Why can’t there be a universal circuit board that transforms into any device simply by loading different software?”
Alice remained silent. She gripped the textbook *Principles of Communication* tightly in her hand and stepped across the threshold.
Behind her, a new line of characters quietly appeared on the lintel after she passed through—engraved beneath the original line, smaller in font size but even clearer.
“This is the answer.”
(To be continued. Next chapter: Entering…)“Traditional Radio Fortress”——Seeing each function permanently fixed in its own isolated room, one understands why.“Hardware Is Function”It’s a dead end. And that chief engineer will show Alice the last glimmer of the old world.……🏰🔒📻）
[Opening: Knowledge Review]
This chapter lays the groundwork for the following core concepts:“Fairy Tale Seed”：
| Communications / Software-Defined Radio (SDR) Concepts | Fairy Tale Incarnation |
| The Core Concept of SDR—Hardware Reconfigurability | Alice countered, “Why can’t there be a universal circuit board that becomes whatever device you need simply by installing the corresponding software?” |
| Limitations of Traditional Radios (Hardware-Centric Design) | In communication theory textbooks, different functions correspond to different circuits, which are not interchangeable. |
| Basic Definition of Software-Defined Radio (SDR) | The phrase above the lintel: “Hardware is the body; software is the soul.” |
| Signal Processing Flowchart / Flowgraph Programming | Colorful building-block modules continuously rolling on the shaft wall |
| GNU Radio software framework | “GNU Radio” on the White Rabbit T-shirt |
| USRP hardware platform | The blue circuit board in the White Rabbit’s arms |
| Connection with the First Part | Alice has finished studying the principles of communication; Flowchart Cat is Spectrum Cat’s “younger brother.” |
Preview of the Next Chapter
Alice walks in“Traditional Radio Fortress”, seeing the AM radio room, FM radio room, and telegraph room……The function of each room is hardwired. The chief engineer told her:“Our castle has114a room, corresponding to114various radio standards——A new room must be created for each additional standard.”Alice asks:“Then what if there is a universal circuit board?”The Chief Engineer shook his head and smiled.……🏰🔐📡
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