Once We Lived in Nanjing

Ban Xia held a small green PCB board in her hand, examining it under the light. It was slightly larger than her thumb, with a dozen centimeters of wire hanging beneath it, a thin white wire, each end soldered with a similarly sized square circuit board. The board in Ban Xia's hand was marked with a blurry "TX", while the other end was marked "RX". This device was to be plugged into a relay station, connecting a transmitter at one end and a receiver at the other, linking two base stations together.

The PCB board was coated with green solder mask, beneath which you could see neatly arranged wiring. The circuit board was small and simple, arranged with neat rows of silver elongated solder pads, denoted with white English abbreviations.

"Hmm...MIC AUDIO…"

Ban Xia inspected closely.

"PTT."

"GND."

"RX AUDIO."

"COR OUT."

She didn't understand what these abbreviations meant, but she could guess they indicated the functions of the pins.

This was one of the simplest of circuit boards, so basic that it lacked even the most fundamental components. It weighed just a few grams in her hands, yet it encapsulated the peak intelligence of humanity's third industrial revolution. The concept of integration was born from this tiny plastic piece. PCBs replaced complex, bulky physical cables and circuits; people printed intricate, complex circuit designs in two dimensions like drawing, spreading them flat, miniaturizing designs as complex as cities to tiny scales, constructing vast kingdoms of information.

What extent had human civilization reached before the world was destroyed?

The girl lifted her bare feet, creaking back and forth in her chair, raising the circuit board high, squinting one eye, focusing on the tiny circular holes on the board. Perhaps she could understand the sadness and pain of her teacher; this magical creation lay before her, yet she could not comprehend it.

This was an ability humans once possessed.

Now lost.

Ban Xia recalled the days when her teacher was still around. She was young then, and the teacher would take her around scavenging trash, bit by bit building a strong fortress.

Her teacher was from the old era; she knew the pre-apocalyptic world very well. Ban Xia had guessed her teacher's profession, but the latter's multifaceted skills made it hard for Ban Xia to confirm what she had done before the disaster struck. The teacher excelled in wilderness survival, was an excellent marksman, which made Ban Xia think she was a military personnel. Yet, she also knew how to set up electrical networks and repair complex household appliances like an electrician — most astonishingly, the teacher had studied astronomy and aerospace engineering for a long time (Ban Xia didn't know what astronomy or aerospace engineering were, these were words Bai Yang had told her). The teacher had collected a lot of data, but eventually burned it all.

During those years, the teacher would sit in the room flipping through books and drawing, leaving Ban Xia to play with mud outside. Occasionally, Ban Xia sneaked into the room and could see the walls plastered with full draft papers.

"The teacher was definitely saving the world!" Ban Xia said to Bai Yang, "She was finding a way to drive away this apocalyptic disaster!"

"But now there are only the two of you left in the world," Bai Yang asked, "How can that save anything? Can it bring everyone back to life?"

"I don't know about that, but she must have been finding a way," Ban Xia said, "Such a powerful person, the only one to survive the disaster out of billions, isn't that the chosen savior?"

"You're a survivor too, young lady."

"I was just someone she saved, the kind who slows others down," Ban Xia said, "Without her, I wouldn't have survived till now; without me, she probably would have."

"It's a pity the teacher didn't leave any useful information behind," Bai Yang sighed.

"She burned all her materials," Ban Xia said, "Who could have known something like this would happen? I can get in touch with you."

"It would have been better if she left it to you," Bai Yang scratched his head, "Then we wouldn't be as clueless as we are now, not knowing what happened or why."

"But she didn't leave it to me. If you had contacted us five or six years earlier, you could have spoken to the teacher," Ban Xia said, "Since it's all about crossing time and space, why couldn't you push the time five years earlier? The teacher was still alive five years ago, she knew everything."

"That's not something I can decide, young lady," the voice from the other end of the radio said leisurely, "It's rare enough that fate has given us this opportunity; we can't be too choosy. I too wish I were talking to your teacher."

"Oh?" the girl raised her eyebrows, "You don't want to talk to me?"

"No...that's not what I meant," Bai Yang stammered, "I mean your teacher would be more useful…"

"I'm not useful?"

"You are useful!" Bai Yang asserted firmly.

"What use am I?"

"You...you are the last hope of all mankind from ancient times to the present, the most important last person in human history, a priceless treasure, young lady, the highest IQ in the world, the most accurate gun skills,最最 }];

best archery skills, most beautiful appearance, best figure!" Bai Yang blurted out all at once.

Ban Xia's eyeballs rolled around, her lips pursed and curved into a small smile, emitting a gentle snort.

"Hmph."

·

·

·

Thursday.

Wang Ning's bulky body leaned halfway out of the window, holding up two mop sticks high with a two-meter long whip antenna tied to them, sweating profusely.

He was wearing headphones, listening carefully for a while, then shouted towards the neighborhood, "I can't hear anything! Old Bai, have you sent the message yet——?"

"No——!"

Bai Zhen stood far away on the lawn downstairs, with a folding wooden table in front of him. On the table laid a black digital amateur radio station. He tilted his head and clamped his cellphone with his neck, holding a Baofeng UV5R amateur radio walkie-talkie in one hand, and tweaking the digital station on the table with the other.

"Then hurry the fuck up——! I can't hold this position much longer——!" Wang Ning screamed, "My back is breaking!"

"Alright, alright... Yes, okay, no problem, I'll do it in a bit."

"Old Bai, have you fucking sent the message yet——?"

"No——!"

"Then what the hell are you babbling about? What are you saying——?"

"Old Zhao is calling me——!"

"What's up with him, so much bullshit——!"

"How would I know where he's getting all this bullshit from——!" Bai Zhen yelled back at the building, then bowed his head to continue the phone call, "Hmm? It's not you, he said it's his dad who talks bullshit a lot."

This was their sixth experiment of the day.

The scale of the experiment was significant, with relay station, base station, and spectrum analyzer all in use. Wang Ning and Bai Zhen had just preliminarily set up the remotely controlled system. They started experimenting from nine in the morning, busily tweaking equipment until four in the afternoon, hoping to achieve optimal performance.

The devices were placed far apart from each other, at considerably distant locations.

The relay station was connected to a second-hand Icom725, placed on Bai Yang's desk—this was because the shortwave station Icom725 needed to borrow Bai Yang's DP antenna. The 14MHZ dipole antenna, twenty meters long, stretched out like an oversized clothesline on the rooftop, impossible to set up temporarily, only borrowable as is.

And for the relay station's required antenna, it used a 144MHZ whip antenna, two meters in length. In their modification plan, they opted out of using a duplexer, so crudely used two antennas, one for the transmitter and one for the receiver, each managing their own, both held by Wang Ning outside the window.

To avoid interference, Wang Ning should keep the two antennas as far from each other as possible, so at that moment, he looked like Ultraman with his arms raised high outside the window.

Truth be told, this pose was a bit thrilling, like he was about to launch into space and fly towards the universe.

Meanwhile, Bai Zhen brought over another amateur radio station, a borrowed Icom705.

Bai Zhen carried a folding table downstairs, set it up on the lawn of the neighborhood, but was chased away by the security guard.

He found another spot on a pathway, set up the table, placed the Icom705 amateur digital radio station on it, set up the antenna, but the security guard came again, leading to a long argument.

The new security guard found the middle-aged man suspicious, the equipment suspicious, the credentials suspicious.

Bai Zhen asked, don't you know what HAM is? I am a HAM.

The security guard said if you're a frog, please go back to your pond.

With a UV5R in his hand, the Icom705 on the table, and an antenna set up beside him, Bai Zhen was responsible for testing the remote control system in the command center.

The equipment would form the following signal linkage:

During receiving tests, Bai Zhen would use the UV5R outside to send messages, which the GR3188 relay station received. The relay station's receiver then transmitted the signals to Icom725.

During transmission tests, Wang Ning used the Icom725 in the room to send signals, which were transmitted to the GR3188 relay station. The relay station's transmitter then sent the signals to Bai Zhen, with Bai Zhen's Icom705 amateur radio station responsible for reception.

If both sending and receiving worked without issues, then BG4MSR could replicate a completely identical system.

Due to a severe shortage of manpower, Wang Ning and Bai Zhen had to serve multiple roles single-handedly. Bai Zhen took the handset downstairs, distancing himself, while Wang Ning stayed listening to signals with his headphones, also holding up the antennas as a human rack.

"Attention, attention, all departments," Bai Zhen pressed the PTT button on the UV5R, "Reverse the Future, Save the World Amateur Radio Emergency Command, the sixth experiment of the remote control system starts now!"