Once We Lived in Nanjing

"Thank... thank you."

Bai Yang and his two friends stammered their thanks, utterly astonished, and before they had the chance to say more, the waitress had already set the tableware, given a slight smile, and quickly disappeared from sight.

Having finished dinner without further incident, Bai Yang hurried home after evening self-study, ready to seek explanations for the mystery at hand. He wanted to know what exactly those people told the school, as the teachers' looks made him feel as if his days were numbered. But as soon as he got home, he found a crowd chatting merrily in his bedroom, which gave Bai Yang quite a shock—

"Right, right, right, exactly, the Zifeng Building. It's only a five-minute walk from there."

"Wait a second, we're looking at the map."

"Look for it! Old Wang, see if there is a shortcut nearby?"

"How fast can that big eyeball move? Let's see if we can estimate a safe range..."

Bai Yang pushed open the door: "What are you doing?"

The three old men turned their heads in unison, looking as if they'd just been caught plotting something nefarious.

"We're chatting with the young lady."

His dad held the hand mic, with Wang Ning and Zhao Bowen standing on either side of the chair—one holding a large map, the other with a tablet computer in hand.

"You've already connected with her?" Bai Yang was somewhat surprised; he glanced at the time—it was just eleven o'clock, "This early?"

"Even earlier than you think." Zhao Bowen said, "We made contact three hours ago."

"BG4MSR, my son has just come back from school, it's your turn to chat, OVER." Old Bai happily gave up his spot and left the hand mic on the table.

"But... isn't it only after eleven o'clock that we can make contact? How come it's so early today? Three hours ago?" Bai Yang squeezed over after dropping his backpack, and the crisp voice of a girl came from the Icom725 radio speaker: "BG? BG4MXH? Are you back?"

"It's me, I've just returned, OVER." Bai Yang replied holding down the hand mic, then turned to ask his dad, "What's going on? It's not even the time yet?"

Their experience over the past few months had taught them that the radio could only reach BG4MSR after eleven o'clock at night; any other time was unsuccessful. Bai Yang had not failed to experiment—he had specifically tried at nine o'clock in the morning, noon, six o'clock in the evening, and eight o'clock at night on a weekend, but none of the attempts succeeded.

Only after eleven o'clock at night was communication guaranteed to be successful.

"It's because we've advanced a step further in our understanding of it." Zhao Bowen pointed to the radio, "We found indirect evidence that the new moon is an important factor affecting Super Space-Time communication."

"What kind of evidence?"

"The evidence is frequency." Zhao Bowen replied, "It was just a hypothesis at first. During the time we took this radio out for inspection, there were several theories within the team regarding the cause of Super Space-Time communication. Today we successfully validated one of them—"

"I really can't stand your roundabout way of talking." Old Bai complained, "Can you get to the point?"

"I have to make the context clear, don't I?" Zhao Bowen rolled his eyes, "If you can, go ahead and explain."

"I will explain then!" Old Bai snorted, "Actually, the reason is quite simple. The reason we could connect with BG4MSR earlier is that it has always been there."

Bai Yang didn't understand what that meant.

"That's right, you could actually make contact with BG4MSR as early as seven o'clock in the evening—it's always been possible." Zhao Bowen added, "There's no need to wait until after eleven at night."

"But I've tried." Bai Yang was very surprised, "It didn't work at all!"

"Because your frequency was wrong." Old Bai said.

"14.255Mhz." Bai Yang said.

"At around seven or eight in the evening, she's not at 14.255Mhz." Old Bai explained, "That's the key."

Bai Yang was baffled.

"Then where is she?"

"Probably around 14.305Mhz." Old Bai answered, "That's what our testing found out."

Bai Yang didn't believe it, so he decided to grab the handheld transceiver and ask directly, "BG4MSR, BG4MSR, I have a question - do you adjust your radio frequency at night? OVER."

"Adjust frequency?" the girl said, "No, I always stay on 14.255Mhz."

"Listen, she said she hasn't adjusted the frequency." Bai Yang leaned back in his chair nonchalantly.

"Of course, she hasn't adjusted the frequency, but frequency changes are not always man-made," Zhao Bowen explained. "You know about Doppler radar, right? It's used to calculate the speed of a target based on the changes in radar wave frequency. This principle is also commonly used in amateur radio activities."

"Working the satellites," Bai Zhen said.

So-called satellite working is a fairly common amateur radio activity. In addition to direct frequency communication, relay stations, and ionosphere reflection, HAMs can also rely on man-made satellites orbiting above to engage in amateur radio activities. These satellites that handle relay transfers of amateur radio signals are known as amateur satellites - for instance, those developed by Harbin Institute of Technology, such as the Lilac series of satellites, and of course the International Space Station, which plays a significant role in the world of amateur radio (the International Space Station is a super-large amateur satellite). Anyone can make long-distance calls through amateur satellites, but it's important to remember that amateur satellites are low-Earth-orbit satellites, different from geostationary satellites. Low-Earth-orbit satellites don't maintain a stationary position relative to the ground; they fly by at high speeds - once there's relative velocity, electromagnetic wave's Doppler effect becomes an influential factor that cannot be ignored.

When the satellite is inbound, due to the quickly decreasing distance, the electromagnetic wave is compressed and its frequency increases; when the satellite is outbound, with the distance growing, the electromagnetic wave is stretched and its frequency decreases. This principle is the same as listening to the changing whistle of a train as it enters or leaves a station.

Therefore, when HAMs are working satellites, they must adjust their transmit and receive frequencies according to the satellite's position. This is called Doppler shift.

"I know all that."

Bai Yang certainly knew what the Doppler effect was, but why would it affect him and BG4MSR if they weren't communicating through a satellite?

"Don't rush, wait until we've finished," Zhao Bowen said. "Based on current experiments, we can draw a preliminary conclusion: around six-thirty, we can faintly capture a bit of the signal, and after seven, the signal becomes clear enough for normal communication; at that time, the frequency is 14.305Mhz, which is a lot higher than 14.255Mhz. Why is that?"

Bai Yang thought for a moment.

"Because something is coming into orbit?"

"After midnight, past two in the morning, the optimal communication frequency drops to 14.235Mhz. Why is that?"

Bai Yang thought for a moment.

"Because something is departing orbit?"

"What exactly is this thing coming and going?" Zhao Bowen asked, "Think about the timing; what could possibly appear at six-thirty in the evening? Reach a stable position by midnight? And then begin to move away after midnight?"

Bai Yang slapped his forehead.

"The Black Moon."

"Correct, that's the indirect evidence we've found. The changes in the radio frequency coincide with the positional changes of the Black Moon. The Black Moon must be a significant factor influencing Super Space-Time communication, and this is the first substantial evidence we've found," Zhao Bowen said. "The rate of frequency change is about 10Khz per hour, which is a substantial change in frequency. Therefore, you couldn't contact BG4MSR before eleven, because she was out of your reception range at that time."

Bai Yang understood now.

He couldn't get in touch with BG4MSR during the day because the Black Moon wasn't in the sky.

He couldn't reach BG4MSR before eleven o' clock because the frequencies didn't line up.

In SSB mode, the bandwidth occupied by transmissions is very narrow (note that sending any information will occupy bandwidth; if a station transmits on a frequency of 15.000Mhz, in reality, it occupies a range of frequencies centered on 15.000Mhz, not just a single point at 15.000Mhz). Generally speaking, among various radiocommunication methods, frequency modulation (FM) occupies the most bandwidth, followed by amplitude modulation (AM), then SSB, and finally CW (Continuous Wave) which is Morse code and occupies the least bandwidth. However, CW can only send dots and dashes while the advantage of SSB is that it allows you to converse directly and occupies a very narrow frequency band. Bai Yang's SSB mode utilizes bandwidth of roughly 20Khz, centered mainly around the narrow range from 14.255Mhz to 14.275Mhz. Once the other party's signal exits this range, he won't be able to receive it.

Using midnight's 14.255Mhz as the base, and calculating with the rate of frequency shift at 10Khz per hour, the frequency in the first half of the night would be higher than this figure. At seven in the evening, BG4MSR's frequency was 14.305Mhz, at eight o' clock it was 14.295Mhz, at nine it was 14.285Mhz, only beginning to enter Bai Yang's receivable range around ten o' clock.

This was the first time Zhao Bowen and his colleagues confirmed the significant impact of the Black Moon on Super Space-Time communication.

"We have always speculated that the Black Moon is the cause of Super Space-Time communication, but today we managed to confirm it," Zhao Bowen continued. "We had BG4MSR cooperate with our experiment, logging on at seven this evening to test the frequency changes, and guess what? What we thought was correct."

"Why would it have this kind of effect?" Bai Yang was baffled. "The Black Moon isn't a relay either, the signals aren't directed towards it, so why would it cause the Doppler effect?"

"Right, you both didn't use directional antennas; you need a Yagi antenna to work the satellites. The Black Moon isn't a relay, so this Doppler effect isn't caused by the Black Moon's movement," Zhao Bowen nodded. "So, we speculate further that its influence goes deeper - this hypothesis is very bold... It wasn't proposed by me, I'm not that radical yet. A comrade from the Physics Institute said that time and space are inseparable. Since the Black Moon affects time, we cannot expect space to remain unaffected. The Doppler effect on radio signals is just an external manifestation of the Black Moon's influence on space..."

"What's actually changing is not the frequency of the radio waves, but the space in which the radio waves exist," Zhao Bowen paused. "The Black Moon may be pulling and compressing space on a large scale."

(Author's idle chatter: I've grown a year older today.)