Wednesday.

Wang Ning, relying on his bottomless connections and even more bottomless thick skin, acquired a second-hand GR3188 repeater from Nanjing’s HAM community. That same day, he had Xiao Zhu drive it to headquarters. The base station used in the repeater was the same model as the one Ban Xia had found, a Motorola GM300.

That evening when Bai Yang returned home from school, the living room had transformed into a large-scale second-hand electronic waste collection station. Old Wang and his father were squatting among scattered electronic components, screwdrivers, and wrenches, surrounding the Icom 725 radio and GR3188 analog repeater, looking just like two computer repairmen making a house call.

“Give me the diagram, I need to find where this COR OUT interface is…”

“Where’s the multimeter? Did you bring it? I’ll have Xiao Zhu deliver one.”

“Damn, we need a soldering iron to connect these wires, right? Can they find a soldering iron over there? And what about rosin?”

“What are you worried about? You think we can’t find a soldering iron in all of Nanjing?”

“Damn, where was this repeater used before? Why won’t it clean up? It’s leaving black marks everywhere, dirty as hell.”

“Get a rag!”

Bai Yang threw his backpack on the bed in his room. His mom sat on his bedroom bed scrolling through her phone and looked up to call out: “Yang! Food’s in the pot in the kitchen!”

“Got it.”

Bai Yang opened the pot lid in the kitchen; inside were warm noodles.

He carried his bowl back to the living room and squatted beside Wang Ning and Bai Zhen. The two middle-aged men were completely absorbed in their work. They had opened the repeater’s outer casing, and removed the cooling fan, exposing all the interfaces and the complex tangle of cables.

“This is so complicated,” Bai Yang said while slurping his food. “Can she handle it?”

“It’s not complicated at all,” Wang Ning said while unscrewing something. “Once you understand the internal technical logic, the operation is very simple… Shit, it broke!”

“You know how communication networks are divided into seven layers, right?” Bai Zhen said. “The bottom layer is hardware, the upper layers are protocols. What’s important is the upper structure. As long as you understand the logic of the coding, the hardware can be dealt with. For example, if you have image transmission capability, whether you’re using a 4K LCD or an old black and white TV, you can still watch ‘Avatar’ – the only difference is picture quality… Damn, it broke again!”

“This thing is very simple in principle, I’ve explained it to you before – it’s just the repeater controlling the two-five’s transmission and reception. When you use a handheld radio to contact the repeater remotely, you can achieve the effect of a mobile phone.” Wang Ning forcefully pulled out a small green printed circuit board from the repeater, about the size of a thumbnail, connected to a thin white wire. He held it up to show Bai Yang. “Look, this is it. You’ll use this to connect the repeater and the two-five. As long as you find the right interface and pins, it can accomplish many tasks.”

“Almost all the cables in this room have a copper core, but they transmit different types of signals,” Bai Zhen pointed around. “Same hardware foundation, different network protocols.”

“So…” Bai Yang hesitated, “we still have to teach her the OSI seven-layer model?”

“Theory combined with practice would be best – teaching her to understand the TCP/IP protocol would work too,” Wang Ning nodded.

“But even I don’t understand it,” Bai Yang said with his mouth full of noodles, speaking unclearly. “How could I possibly teach someone else?”

“How can you not understand?” Wang Ning gave him a strange look. “Isn’t this common sense?”

“How can you not understand?” Bai Zhen also gave him a strange look. “Isn’t this common sense?”

After holding it in for a while, Bai Yang angrily counterattacked:

“How come you two couldn’t get into university? Isn’t that just basic competence?”

“Hmm… BG4MXH, this sounds so difficult,” Ban Xia was quite troubled.

She had paper and pen on her desk, ready to be a good attentive student, but the other party started by bombarding her with a bunch of network protocol English abbreviations that made her dizzy – TCP, UDP, ICMP, this P and that P, comparable to a student who just learned addition and subtraction opening volume ten of Landau.

“BG4MXH, I don’t understand any of this, it’s so hard. Do I have to learn it?”

“This is a theory, OVER.”

“What’s the use of theory?”

“Theory has no use, OVER.”

“Then…” Ban Xia carefully asked, “If it has no use, can I not learn it?”

“You don’t have to learn it, OVER.”

Bai Yang was straightforward.

Ban Xia cheered on the other end, accompanied by the sound of dropping her pen.

As someone living in the post-apocalyptic era, she experienced for the first time in her life the immense joy of having an exam suddenly canceled.

What a precious experience.

“Young lady, let me tell you, anyone who forces you to learn complex theoretical knowledge is a demon. Is there anything more useless in this world than conic sections, quadratic functions, sequences, and sets? No! And if there is, it would be calculating how many circles a charged particle can make in electric and magnetic fields… Math can go to hell! Physics can go to hell! Let math and physics go to the devil!”

“Math can go to hell! Physics can go to hell!” Ban Xia joined in shouting, “Let math and physics go to the devil!”

“Math exams and physics exams can go to the devil!” Bai Yang shouted slogans, “Down with the three mountains of math, physics, and chemistry!”

“Down with the three mountains of math, physics, and chemistry!”

“Liberate high school seniors worldwide!”

“Liberate high school seniors worldwide!”

“Get back to work,” his father knocked on the door from outside. “Otherwise, when all the high school seniors in the world are dead, who will you liberate?”

Ban Xia opened the casing of the GR3188 repeater. Under Bai Yang’s guidance, she needed to first understand the repeater’s structure. The GR3188 analog repeater’s structure was quite simple – to put it plainly, it was crude and straightforward. Opening the back cover revealed the cooling fan and messy cables. After removing the fan, you could see the interface ends of the internal base station. The basic components of the GR3188 were two base stations, plus the repeater control board and duplexer, stacked in three layers from top to bottom.

Most of the repeater’s components didn’t need to be modified by Ban Xia. As Wang Ning put it, the repeater’s hardware itself was sufficient to support her needs – just like how a movie that can be played on a color LCD screen can also be played on a black-and-white TV. What Ban Xia needed to do was find the right interfaces and plug the correct connectors into the correct interfaces. Only experienced veterans knew how to make the connections properly, which was why she needed Wang Ning and Bai Zhen’s complete guidance.

Bai Yang was very relieved that building the remote control system didn’t involve very precise operations and didn’t require Ban Xia to hold a soldering iron to solder PCB boards – that would have been like pushing a duck onto a perch.

“Young lady, now tell me what you see, OVER.” Bai Yang asked, holding the mic.

“Umm…” The girl wore headphones with the GR3188 repeater on the table in front of her. Ban Xia tilted her head to peer into the chassis. “I see lots of wires, red ones, black ones, and white ones, some thick and some thin, all messy.”

“What else? What else is inside the chassis? OVER.”

“Inside the chassis, there are also the backs of two amateur radio stations, stacked one on top of the other, fixed in the chassis with screws, can’t take them out,” Ban Xia continued. “There are several thick wires plugged into the backs of the radio stations.”

“Don’t touch those, what else? OVER.”

“There’s also a black iron box at the very bottom of the chassis, I don’t see any openings, it’s sealed.”

“You don’t need to touch that either,” Bai Yang said. “Young lady, listen carefully, I’m going to tell you which interfaces we need to use and which ones we don’t need, OVER.”

“Mm-hmm, I’m listening.” Ban Xia nodded.

“First count how many wires are plugged into the backs of the two base stations,” Bai Yang instructed. “How many sockets are there, OVER.”

“One… two, three…” the girl started counting. “Six wires, six wires in total, three plugged into each radio station. There’s one that’s the thickest, black, with a wide flat connector, another black one with a round connector, and finally a white one, the thinnest, this wire connects to a black rectangular plastic piece plugged into the back of the base station…”

“That’s a green plastic piece, OVER,” Bai Yang said.

“Green?” Ban Xia’s eyes widened. “No, I see it as black.”

“That’s because there’s too much dust, it’s too dirty,” Bai Yang said. “That plastic piece can be pulled out. Pull it out and wipe it clean, OVER.”

A moment later, the girl’s exclamation came through the headphones.

“It is! It’s green! And it has circuits on it!”

“Right, this is a PCB board, that is, a printed circuit board. Printed boards are green,” Bai Yang explained. “The interface we need to use is this one, this thin white wire. It will connect the repeater and the 725. Can you understand that? OVER.”

Ban Xia nodded, seeming to half-understand.

“I understand.”

BG4MXH once said that class is learning, and learning in class. Taking classes and learning are trials everyone must go through while growing up. Every child at age seven must forcibly enter the prison and concentration camp called school, losing their freedom from then on, only to be liberated after at least age twenty-two. Now as Ban Xia looked at the black box-like repeater before her, thinking about how she must understand it, she suddenly realized that even the world before the apocalypse wasn’t good everywhere.

Not having to go to school – that was truly good.