Once We Lived in Nanjing

Over the upcoming weekend, Bai Zhen and Wang Ning began designing a remote communication system.

In plain terms, it meant enabling BG4MSR to use mobile phones.

This was crucial.

The immediacy and convenience of mobile phones far surpassed those of landlines—it was time to upgrade that girl's mode of communication.

"The logic of the technology is very clear, it's not hard to achieve," Wang Ning said, sitting on the couch and stroking his stubbly chin, "Fundamentally speaking, we just need to create a..."

"Relay station," Bai Zhen sat opposite him.

"Yes, we just need a relay station," Wang Ning nodded.

Such a relay station is an extremely common yet essential infrastructure in amateur radio.

As is well known, nowadays more people use the UV band than shortwave; to utilize the UV band, one only needs to spend a hundred yuan on Taobao and Jingdong to buy a handheld, which isn't much bigger than a mobile phone. It's compact, easy to carry, comes with a flashlight, and with a couple of button presses, the flashlight can even temporarily blind you—it's not like shortwave that requires a bulky base station. However, the UV band has its pros and cons. UHF and VHF frequencies are much higher than shortwave, and anyone who studied high school physics knows that higher frequencies mean shorter wavelengths; shorter wavelengths mean a reduced ability to bypass obstacles.

Thus, UV band radio waves propagate line-of-sight; they can only reach as far as you can see. If there are obstructions, the signal will be blocked.

They cannot be reflected via the ionosphere like shortwave.

But with modern cities filled with towering buildings and myriad obstructions, how do people using the UV band manage long-distance communication?

Thus, people consider putting a repeater on high places.

This replcement system can be placed on towers, mountain tops, even satellites—it needs to be installed at a high point visible to everyone—HAM handhelds of the UV band first send the signal to the repeater, which then forwards it.

A repeater, positioned high, sees far and can transmit signals to distant places; amateur satellites or the International Space Station, orbiting hundreds of kilometers high, can even support transcontinental communication.

Such a replacement system is known as a relay station.

"Relay?" Bai Yang, still somewhat perplexed, didn't understand how to utilize a relay station to establish remote control, "How do we do that?"

"Bai, if I ask you to design it, to allow BG4MSR to communicate with us from afar using only two connections, how would you do it?" Wang Ning countered.

Bai Yang paused, pondering for a few seconds.

"Uh...a radio communication link should be established to allow both...BG4MSR to transmit the signal over a long distance to Icom725, then Icom725 transmits it to us."

"Right, your approach is correct," Wang Ning approved, "But how exactly should it be done?"

"She should have a portable handheld as the terminal for sending and receiving messages," Bai Yang further speculated, "She sends the signal to Icom725 through the handheld, then Icom725..."

At this point, Bai Yang suddenly halted.

"Forwarding."

He realized that at this point, the role of 725 in the entire chain is to forward—it receives the signal from the girl's handheld and forwards it to Bai Yang.

How can 725 be made a forwarding node?

All functions of such an antiquated device like Icom725 must be manually handled—press the button on the handheld to speak, release it to listen. How could this pressing and releasing be remotely operated?

You aren't a robot; you can't travel tens of thousands of miles and still leave a hand in the room just to press buttons.

"725 alone can't manage it," Bai Yang slowly stated, "Definitely need a peripheral that can both transmit and receive radio waves on its own and control the 725's transmission and reception. Whenever there's information to send, it controls the 725 radio to send, and receive whenever there's information."

"Intuitive, very intuitive, Bai," Wang Ning smiled, "Just like you thought, we need exactly such a peripheral."

"This peripheral is the relay," the old father said.

"Exactly, it's the relay," Wang Ning nodded, "Bai, do you know the structure and working principle of a relay station? That kind of purely analog relay station... we'd better use a purely analog one as digital relays or hybrid digital-analog relays are somewhat complex, fearing the girl over there couldn't handle it, and also fearing such delicate devices wouldn't last long. The structure of an analog relay is simple enough that you could DIY it using two walkie-talkies."

"Because the basic structure of a relay station is just two amateur radios put back-to-back," Old Bai took over the conversation, explaining to Bai Yang, "The main component of a relay is just two base stations coupled with a duplex device; if you use two separate antennas, you can even omit the duplexer. It operates very simply; one base station receives signals, the other transmits them..."

Old Bai pointed at his son.

"For example, you're a handheld, I'm a relay; you talking to me is like sending a signal to me, my ears are the receivers, my mouth is the transmitter, I'm made up of these two devices. When my ears hear what you say, I use my mouth to relay your words to Old Wang, and when Old Wang talks to me, I can relay his words to you, get it?"

Bai Yang nodded thoughtfully.

"I understand this, but why can it do remote control?"

"The key is here, didn't you just say we need a peripheral that could automatically control the 725's transmission and reception?" Wang Ning said, "Just so happens, a relay station operates automatically; it's normally unattended."

"Some relay stations are mounted on mountain tops, some on high towers, and even on satellites," Bai Zhen added, "So most relay stations operate unmanned."

"This means it has a mechanism for automatic switching between receive and transmit," Wang Ning explained as he picked up a marker from the sofa and propped a small whiteboard on his thigh, "We need this mechanism to replace manual operation of the send button on 725. Bai Yang, take a look."

As he spoke, he drew a rectangular box on the whiteboard, and inside the box, he drew two elongated rectangles, one above the other.

He wrote "Receiver" on the upper small rectangle and "Transmitter" underneath it.

Finally, he connected the two rectangles with an arc.

"This is a relay station."

Wang Ning pointed to the large rectangle with his marker.

"It consists of two radios."

He pointed to the two smaller rectangles inside with his marker.

"Normally, once the receiver at the top receives a signal, it triggers the transmitter below to forward the signal. But if we dismantle this relay and connect the receiver and the transmitter separately to 725..."

Wang Ning drew another box next to the relay station.

Then he labeled the box with 725.

He then erased the arc, disconnecting the contact between the two small boxes within the relay station, and connected them to 725 with straight lines.

"Then, at this point, once the receiver receives a signal, what gets triggered is no longer the transmitter, but 725—do you understand? The communication link will be as follows: BG4MSR will transmit the signal to the receiver using a handheld transceiver, the receiver controls 725 to enter the transmit state, and 725 sends the signal across super space-time to our side."

"What about us sending signals over?" Bai Yang asked.

"That would be the inverse of this process!" Wang Ning replied, "We send signals across super space-time to her 725, 725 receives the signal, triggers the transmitter below, and the transmitter sends the signal to BG4MSR's handheld transceiver."

He then made a large circle with his marker, enclosing all the components.

"That is the basic logic of the entire link!"

Bai Yang gazed at the drawing on the whiteboard for a long while, then turned to look at Wang Ning's hairless head which seemed to be shining with the glow of wisdom.

"That's amazing."

"In this process, 725 no longer plays a role as just a radio." The father spoke, "but as a super space-time antenna."

The technical logic had been sorted out.

Next was to devise a plan.

"First, we need to determine the aim of our plan. Let's decide what effect we want to achieve," Wang Ning picked up the marker from the sofa, flipped the whiteboard over, and looked up at Old Bai, "The first point is remote control, right?"

"Yes, remote control," Bai Zhen nodded, "We need to make it so that MSR can communicate with this side normally even if she's not in front of the console, not sitting in a chair, but in the next room, outside the house, or even several kilometers away."

"And what are the specific operational requirements?"

"It's best if it could function like a normal handheld transceiver," Bai Zhen answered, "She holds the handheld, presses PTT, and talks."

"Okay, then the requirements are as follows... First, separate human from station, remote control, second, must be simple to operate, easy to learn," Wang Ning nodded, noting each point down on the whiteboard.

"There's... another point," Bai Yang raised his hand.

"Go ahead, Bai Yang."

"It must not cause damage or destruction to the radio itself," Bai Yang cautioned.

This point was crucial. No matter what the father and Uncle Wang intended to do, they could not affect the Icom 725 radio itself, which thus far they did not understand how possessed the ability for super space-time communication; to everyone, that old 725 was a black box, and in this case, the wisest choice was not to tamper with it.

Previously, Bai Zhen, Wang Ning, and Zhao Bowen had recklessly dismantled the unit, opened up the radio's casing, luckily without causing any consequences.

"Good... Third, it must not affect the normal operation of the radio," Wang Ning noted.

Lastly, he raised the whiteboard high for everyone to see.

The writing was scribbly but eye-catching.

First, separate human from station, remote control!

Second, simple operation, easy to learn!

Third, must not affect the radio's normal function!

These three points would be the framework they must adhere to as they pushed the plan forward, striving with all their might with these objectives in mind, to upgrade the communication tools in the hands of BG4MSR; when the experts at the Reverse Future World-saving Amateur Radio Emergency Communication Command Center fully mobilized, their wisdom would be unstoppable!