After crossing the threshold, Alice walked for about ten minutes before she saw the first building.
It was a castle. But it bore no resemblance to any castle she had ever imagined—rather than towers, walls, and drawbridges, it consisted of countless rooms. These rooms were densely packed together like a honeycomb, each with its own door, its own window, and its own antenna protruding from the roof. Some rooms were large; others small. Some antennas were thick; others thin. Warm yellow light glowed from some windows, while cold blue light flickered from others.
A massive bronze plaque hung above the castle’s main gate, engraved with:
“Traditional Radio Castle — Founded in 1895, Ended?”
Alice noticed the question mark after “Ended.” It had been carved deeper than all the preceding characters—as if added later, or as if the answer had never been filled in.
She pushed open the castle’s grand entrance.
I. One Hundred and Fourteen Rooms
Inside lay a long corridor, lined on both sides with countless doors. Each door bore a label:
• “AM Broadcast Receiver — AM”
• “FM Broadcast Receiver — FM”
• “Telegraph Transceiver — CW”
• “Analog Television Receiver — PAL Standard”
• “First-Generation Mobile Phone — 1G (Analog) Base Station”
• “Second-Generation Mobile Phone — GSM Base Station”
• “Third-Generation Mobile Phone — CDMA Base Station”
• “Wireless Local Area Network — Wi-Fi 802.11b”
• “Satellite Communication Terminal — L-Band”
• “Radar — Pulse Doppler”
Alice walked down the corridor—and the farther she went, the more rooms she discovered, seemingly endless in number. Some labels looked freshly engraved; others had faded and yellowed, their edges curled. Even at the corridor’s far end stood a room under construction, where carpenters and welders bustled about, and a temporary sign hung on the door: “Fifth-Generation Mobile Phone — 5G NR (Under Construction).”
“One hundred and fourteen rooms,” a voice said behind her. “Oh—no, one hundred and fifteen now. The 5G room was topped out this morning.”
Alice turned around.
An elderly man stood there, dressed in dark gray workwear and wearing a badge that read “Chief Engineer.” His uniform was pocked with tiny burn holes from soldering iron splatter, and three screwdrivers of different models protruded from his pockets. He looked utterly exhausted—not the fatigue of a single long day, but the deep weariness of a lifetime spent working.
“One hundred and fifteen rooms?” Alice asked.
“More precisely,” the Chief Engineer sighed, tapping his cane against the floor, “one hundred and fifteen distinct radio standards. Each standard requires its own dedicated room—because every radio system demands unique circuitry: different frequencies, different modulation schemes, different encoding protocols, different hardware architectures. An AM radio circuit cannot receive FM signals; 1G base station hardware cannot be upgraded to 2G; a Wi-Fi router cannot function as radar.”
“So every time a new standard emerges, you…?”
“We build a new room,” the Chief Engineer said. “Then we weld a new circuit, install new antennas, and run new power cables. Over and over again—from 1895 to today, without pause.”
He pushed open the nearest door. Its placard read: “AM Broadcast Receiver — AM.”
II. A World Soldered Shut
The room was small—about the size of an ordinary bedroom. In its center sat an AM broadcast receiver: wooden casing, brass knobs, exquisitely crafted. Yet upon closer inspection, Alice realized—every wire inside was permanently soldered in place. Resistors soldered directly onto the PCB, capacitors soldered beside them, diodes soldered behind the capacitors. Every conductor lay fixed, rigid as a corpse nailed into a coffin.
“See?” said the Chief Engineer. “This receiver is superb—it delivers clear, stable, durable reception of medium-wave AM broadcasts. But it can do only this one thing. Want it to receive FM? Impossible. Shortwave? Impossible. Turn it into radar? Even more impossible.”
He pointed to a row of solder joints at the back of the receiver: “These joints are permanent. To replace even a single component, you must desolder the old one and resolder the new one—meaning you must redesign the entire circuit, fabricate a whole new board, and re-tune all parameters.”
“That’s basically… building a brand-new unit from scratch?” Alice asked.
“Exactly. Upgrading equals rebuilding.” The Chief Engineer said. “That’s why we have our one hundred and fifteenth room.”
Alice opened the next door—the “FM Broadcast Receiver — FM” room. Inside sat an FM receiver, also with a wooden case—but its internal circuitry was entirely different. Comparing the schematics of the two machines, Alice found not a single matching trace.
“They’re doing essentially the same thing—receiving broadcast signals,” Alice observed. “Yet their hardware isn’t interchangeable at all?”
“Not at all,” the Chief Engineer nodded. “Can an AM radio suddenly receive FM signals?”
Alice thought for a moment—and shook her head.
“That,” he said, “is the old world. Each function requires dedicated hardware. Every additional function demands another permanently soldered circuit. All one hundred and fifteen rooms in this castle house circuits custom-built for exactly one purpose—and useless for anything else.”
III. ‘Communication’ Between Rooms
Alice stepped out of the radio room and continued down the corridor. She noticed something strange—the floor featured semicircular grooves spaced every few meters, worn smooth and shiny by repeated foot traffic, clearly polished by metal friction.
“What’s this?” she crouched down to ask.
“Transportation channels.” The Chief Engineer replied. “Sometimes rooms need to ‘communicate’—for example, when the AM room receives a signal and must pass it to the FM room for processing, or when GSM room data needs forwarding via the Wi-Fi room. But because each room uses incompatible interface standards, signals cannot be passed directly.”
“So what do you do?”
“A dedicated department handles the transportation. They convert the AM room’s output signal into printed specifications on paper, walk to the FM room’s door, knock, and say: ‘Here’s what came from AM—you’ll need to recode it for your system.’ The FM room staff then take the specs and reprocess everything according to their own hardware architecture.”
“This…” Alice widened her eyes. “This isn’t communication—it’s manual courier service!”
The Chief Engineer smiled wryly: “You’re absolutely right. This inefficiency is one reason the old world struggles so much. Different standards cannot interoperate directly—like three people speaking English, Chinese, and French sitting together, requiring three translators and three rounds of interpretation.”
IV. The Upgrade Storm
Just as Alice prepared to continue walking, a piercing alarm blared from deep within the castle—not one tone, but dozens of alarms sounding simultaneously at different frequencies and rhythms, like one hundred out-of-tune horns playing in dissonant chorus.
“What’s happening?!” Alice covered her ears.
The Chief Engineer’s face instantly paled. “Here it comes again—the Upgrade Storm.”
The entire castle began to shake. All doors along both sides of the corridor swung open at once. Technicians in varied uniforms poured out, shouting across the hallway. Some held new circuit boards aloft; others dragged coils of cable; still others hung signs reading “Upgrade in Progress — Service Suspended.”
“It happens every year,” the Chief Engineer shouted over the din. “Wi-Fi releases a new version—802.11n upgrading to 802.11ac—so the Wi-Fi room must be completely resoldered. GSM is being phased out, and that room must be converted to LTE. Analog TV transitions to digital—its entire circuitry must be replaced. Mobile networks upgrade from 4G to 5G… and the 5G room isn’t even finished yet!”
Alice witnessed a heartbreaking sight: technicians scurried like worker ants through the corridor—some carrying oscilloscopes, others shouldering soldering irons, still others dragging carts piled high with resistors and capacitors. Every room was being opened, modified, and refitted with new components. Some rooms, due to excessively long upgrades, accumulated dust at their thresholds—old functions already disabled, new ones not yet operational.
“Does this happen every time?” Alice asked.
“Every time,” the Chief Engineer’s voice grew hoarse. “Each upgrade brings the castle to a standstill. Rooms shut down one by one; all technicians work overtime; every circuit is resoldered. Once complete, new functionality goes live—then two years later, another upgrade begins.”
He pointed toward the construction sites at the corridor’s far end: “See those rooms? They’re built for the next generation of standards. While we’re still using 4G, the 5G room is already under construction; while we’re still on Wi-Fi 5, the Wi-Fi 6 room is already in the design phase. Before the old room’s circuits are even fully soldered, plans for the new room have already been drafted. Forever chasing, forever repeating.”
V. Alice’s Question
At last, the alarms ceased. Technicians gradually returned to their respective rooms to resume soldering and tuning. The corridor fell silent—but a profound exhaustion lingered in that quiet.
Alice stood at the corridor’s center, gazing at the dense rows of doors—115 doors, each concealing a soldered-shut circuit, a fixed function, hardware incapable of upgrade.
Then a question occurred to her.
“Chief Engineer,” she asked, “have you ever considered—instead of building each room separately—constructing a single, universal large room? A room equipped with general-purpose circuit boards, universal interfaces, and adaptable antennas. Load an AM software module today to receive AM; load an FM module tomorrow to receive FM; load a radar module the day after to operate as radar. No soldering, no couriers, no rebuilding an entire room with every upgrade?”
The Chief Engineer remained silent for a long time.
He gazed at the tightly closed doors lining both sides of the corridor, at the independent lights glowing from their cracks, at the tangled maze of dedicated cables crisscrossing the ceiling—each belonging exclusively to one room—then let out a soft, low chuckle.
There was no mockery in that laugh.
Only a deep, weary sigh.
“Young lady,” he said, “the ‘universal large room’ you just described—we call it ‘Software-Defined Radio.’ Every engineer in these 115 rooms has dreamed of it. But no one has ever truly built it.”
He turned toward the corridor’s far end, where a door stood apart from the rest—gray in color, unmarked by any label, blank and featureless. No light shone from beneath its crack; it appeared to have remained closed for a very long time.
“Because it’s too difficult,” the Chief Engineer said. “Universality demands ultra-high-speed ADCs, ultra-wide bandwidth, and ultra-powerful processors. It was impossible a century ago. Impossible fifty years ago. Only twenty years ago did serious attempts begin. Today—some are trying, but the road ahead remains long.”
“That door,” Alice pointed to the gray door, “where does it lead?”
The Chief Engineer didn’t answer. He simply shook his head and walked into the nearest room, closing the door softly behind him.
Alice stood alone in the corridor—facing 115 soldered-shut rooms and one sealed gray door.
She remembered the White Rabbit—the figure in the “GNU Radio” T-shirt, holding a blue circuit board.
She recalled the flowcharts on the well wall—constantly reassembling, constantly changing—same base platform, different modular arrangements yielding entirely different functions.
She remembered the inscription above the doorway: “Hardware is the body; software is the soul.”
She walked toward the gray door.
It wasn’t locked.
She placed her fingers at the seam—and gently pushed.
The door opened.
Inside was light—not the warm yellow or cool blue glow of any room she’d seen, but a flowing, ever-changing light, like thousands of lines of code scrolling across an infinitely large screen—or ten thousand signal-processing flowcharts simultaneously rotating, reconfiguring, evolving, and iterating in midair.
She stepped across the threshold.
Behind her, the 115 doors in the corridor emitted a faint, almost inaudible sigh—like 115 soldered functions finally glimpsing a future where soldering was no longer necessary.
(To be continued. Next chapter: “The Software Manifesto”—Alice will meet the “Software Prophet,” see the stone tablet inscribed with “Place the A/D converter as close to the antenna as possible,” and understand why SDR represents the third revolution in communications. And the light behind that gray door will gradually resolve into living spectra—lines of code ready to be written… 🌅📡💻)
[Chapter One Knowledge Recap]
This chapter plants the following core concepts as “fairy-tale seeds”:
| Communication / SDR Concept | Fairy-Tale Embodiment |
| Traditional radio’s “hardware = function” paradigm | 115 rooms, each function tied to a dedicated circuit |
| Incompatibility among radio standards | Inter-room “couriers” manually relay signals |
| Hardware upgrade difficulty | “Upgrade Storm”—each upgrade requires full room resoldering |
| Resource waste and redundant construction | Each new standard necessitates a new room |
| SDR’s “universal platform” concept | Alice’s proposal of “one universal large room”—same hardware board, different software |
| Core pain point solved by SDR | The gray door—the exit from the old world, the entrance to the new |
Preview of Next Chapter
Alice enters the gray door and meets the “Software Prophet.” The Prophet shows her a stone tablet inscribed with a foundational principle: “Place the A/D converter as close to the antenna as possible—the rest is handled by software.” She will witness the third revolution in communications: the leap from hardware to software. Beneath the tablet, a modest line reads: “1992, Mitola—first coined the term.” 🌅📜💡
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