What was the key to hitting satellites?

Tracking.

Low-orbit satellites entered and exited quickly, circling the Earth in just an hour or two, whooshing overhead in an instant. The low-orbit reconnaissance satellite that Old Zhao and the others were sent to the future orbited at just 300 kilometers, completing one orbit around Earth every hour. Such high orbital velocity would present Ban Xia with the same challenge—the little thing moved too fast to track, and if you couldn’t track it, you couldn’t aim at it. Without being able to point an antenna at it, receiving data would be extremely difficult.

“How do you normally track satellite orbits when targeting satellites?” Bai Yang asked.

“We use software, like SatOrbit or Heavens Above. They’re free and show orbital parameters for all public satellites—when they appear, when they pass overhead, which angle, which direction, everything’s crystal clear,” Wang Ning said, sitting in the living room on a small stool, using pliers to straighten a coat hanger. “For more professional needs there’s STK. Similar software is everywhere, leaving no satellite privacy anywhere in the world.”

This software wouldn’t exist in BG4MSR’s era any more—humanity was completely extinct, with no internet, no servers, and no one left to maintain and update them.

“She won’t be able to find the satellite orbit on her own over there, so how will she find it? We’ll just tell her,” Bai Zhen also sat on a small stool in the living room, gripping pliers to cut coat hangers. “If we’re lucky and the satellite re-enters orbit without deviation, once we send her the parameters, she should be able to target it quickly.”

“The best solution would be to bring along a relay satellite and place it in geosynchronous orbit at 36,000 kilometers,” Zhao Bowen likewise sat on a small stool in the living room, holding pliers and straightening a cut coat hanger. “That way, the relay satellite would stay fixed above the girl’s head. The reconnaissance satellite could transmit data to the relay satellite, which would then transmit it back to the ground. No need to waste energy tracking. Otherwise, she’d develop spinal problems standing on the roof all day rotating a Yagi antenna following satellites.”

“Well, why don’t you get them to bring a relay satellite then?”

Bai Zhen snapped his coat hanger with a “crack.”

“I already fucking suggested it and got chewed out by the space team,” Zhao Bowen grimaced. “They asked me if I was even human anymore. Said I wasn’t human at all!”

“So what happened? Did they bring the relay satellite or not?”

Wang Ning also snapped his coat hanger with a “crack.”

“They did, but they warned me it would significantly increase the orbital design difficulty and greatly increase the chances of failed re-entry,” Zhao Bowen answered. “I said we had no choice—can you imagine a young girl standing on the roof all day spinning around with a Yagi antenna? Would she have time for anything else?”

The three old men sat together chattering away, their hands staying busy, like village women sitting together gossiping while knitting—that’s how idle chatter spreads. Instead of knitting needles and yarn, Bai Zhen, Wang Ning, and Zhao Bowen held pliers and coat hangers, with snapping sounds rising and falling.

When Bai Yang returned home from school that afternoon, he found them sitting together torturing coat hangers, and dismembering them brutally. The scene was almost too cruel to watch. It was as if they held some deep grudge against the hangers.

What were they doing?

They were making a Yagi antenna.

The Yagi antenna was undoubtedly the most commonly used antenna type in the HAM community. Compared to ordinary rod antennas and dipole antennas, the Yagi antenna’s advantages lay in its high gain and high directionality, with signals polarized in one direction. In simple terms, other antennas were like light bulbs scattering light in all directions, while Yagi antennas were like flashlights, beaming in just one direction.

Due to this signal polarization characteristic, Yagi antennas were also frequently used by HAMs for satellite communication. Since ordinary amateur radio stations had very low power, and satellites even lower power, communication between radio stations and satellites was like a mute person talking to a deaf person—with thousands of miles between them. Normally, they couldn’t possibly hear each other, unless the mute person mastered the martial arts secret of focusing sound into lines.

This “focusing sound into lines” was the Yagi antenna.

Bai Zhen put down his coat hanger and picked up a thin, long wooden board from the floor, probably scrap material from some furniture factory, about a meter long.

“What are the uplink and downlink frequencies for that relay satellite?”

“Uplink 144MHz, downlink 430MHz,” Zhao Bowen answered.

“U-band transmission speed is a bit slow, X-band would be better,” Wang Ning said.

“X-band reception would be too complicated. The reconnaissance and relay satellites communicate in X-band, and the relay satellite can store data to transmit back to Earth slowly—no rush on that,” Zhao Bowen picked up a measuring tape from the coffee table. “How long should we make the reflector?”

“For the two-meter wave uplink, reflector length should be one meter, half wavelength.”

Bai Zhen took the measuring tape and measured one meter on the straightened coat hanger: “No good, this hanger’s not big enough, can’t get to one meter. Do we have any bigger hangers?”

Mom came out of the kitchen: “You’ve already ruined all the hangers in the house.”

“I’ll have Xiao Zhu buy a bigger one.”

Wang Ning said this while dialing the phone.

That evening, Xiao Zhu ran through all the supermarkets in Qinhuai District.

When straightened, coat hangers became metal wire. Bai Zhen cut a one-meter length of wire to use as the Yagi antenna’s reflector—the Yagi antenna’s construction was so simple, it could be made with wooden strips and coat hangers. This was why Bai Zhen and the others chose the Yagi design: it could be made from readily available materials, was simple to construct, and was extremely beginner-friendly.

The wooden strip formed the central axis, with five straightened coat hangers inserted perpendicular to it in sequence, looking like fishbones forming a character that resembled “豐” (abundance). This made a simple five-element Yagi antenna.

The rearmost and longest coat hanger was called the reflector, responsible for gathering signals, like the mercury bowl in a flashlight.

The second-to-last hanger was called the driven element, the core of all antennas. It was the signal source, where current danced frantically to produce electromagnetic waves.

The remaining three hangers were called directors, guiding the direction of wave radiation, making it radiate in the antenna’s pointing direction to achieve precise targeting.

“Once you finish, will you teach her how to make it?” Bai Yang sat watching the three doing their handicraft. Hand-crafting Yagi antennas was a basic skill for old HAMs. Zhao Bowen had mostly forgotten how, but Dad and Old Wang’s skills weren’t rusty.

“Once we confirm this thing works, we’ll have her copy it exactly over there,” Dad answered. “It’ll have to do.”

“This is simple, easy to learn,” Zhao Bowen said. “With a Yagi antenna, she’ll be able to receive signals transmitted from the satellite and send them to us. All according to plan!”

“How long should the driven element be?”

“96 or 97 centimeters, cut it however you see fit.”

“The remaining three are all the same length.”

“All 88 centimeters.”

“Mind the spacing—do we want higher gain or better frequency band characteristics?”

“Let’s try both. After it’s done we’ll test it on AO-91, and see how it performs… Also, we need to adjust the impedance.”

“Blindly go for 50 ohms.”

“Who brought an SWR meter?”

“No worries, I’ll have Xiao Zhu bring one!”

The trio finally completed a UV dual-band Yagi. When they lifted it pointing east and west, it looked like they were carrying a machine gun—Ban Xia thought so too. Two days later when she finished making her Yagi, she felt that swinging it around was just like Lu Bu from Romance of the Three Kingdoms wielding his Sky Piercer halberd.