I started with a ship full of max-level veterans, and I'm just a complete noob.

The indicator light in the direction finding vehicle dimmed for half a second before returning to normal, and then the instrument rack emitted a low hum.

Lu Qinghe pressed down on the earphone with her left hand, while her right hand spun rapidly on the tuning knob, her fingertips rubbing against the metal texture to produce a soft, rustling sound.

On the oscilloscope, the dip that was originally stopped near 5.3 MHz is slowly shifting.

The interfering bright bands on both sides jump to the left or right at irregular intervals, moving only a small segment each time.

"It's still jumping." Lu Qinghe's voice was hoarse, her teeth biting half a pencil cap. "It was at 5.3 a moment ago, but now it's sliding towards 5.18."

Jiang Ming squatted under the control panel, his knees braced against the crossbar of the metal frame, and two-thirds of the graph paper in his hand was already filled.

He heard Lu Qinghe call out the numbers, and his pen paused on the paper for a moment before drawing an arrow.

The sentry signal from the loudspeaker disappeared along with the frequency hopping, and white noise filled the entire carriage again.

The Yagi antenna on the roof groaned in the wind, and the nuts on the feeder cable, which had just been tightened, rattled from being hit by grains of sand.

"How long did the May 5.18th protests last?" Jiang Ming asked, looking up.

"Eleven seconds." Lu Qinghe didn't turn around, pressing her left index finger against the earpiece, "It's gone, now it's 5:41."

Jiang Ming wrote 5.18 and 5.41 side by side on the paper and put them together with the previous sets of data.

5.30, 5.18, 5.41, 5.27, 5.44.

His pen tip tapped back and forth between the strings of numbers twice.

The spacing is unequal, and the steps are not linear.

However, it is not entirely without rules.

Give me another set.

Lu Qinghe turned the knob faster, his ten fingers trembling intermittently, a reaction to muscle fatigue after prolonged high-frequency operation.

Three seconds later she announced, "5.35."

Jiang Ming filled 5.35 into the sequence and drew a line on the paper with a pencil to connect all the data points.

The differences between two adjacent frequencies are: -0.12, +0.23, -0.14, +0.17 and -0.09, respectively.

He divided the difference by the available bandwidth of 0.8 MHz.

0.15, 0.2875, 0.175, 0.2125, 0.1125.

The pencil stopped.

He multiplied the first ratio of 0.15 by a number, rounded it up or down, and then verified it using the next frequency point.

wrong.

From another perspective, calculate the offset of each frequency hopping position relative to the starting frequency of 4.8 MHz.

0.50, 0.38, 0.61, 0.47, 0.640.55.

0.38, 0.61.

Jiang Ming's breath hitched.

He wrote down three numbers on the paper: 0.618, 0.382, 0.618.

The golden ratio.

Each frequency hop is the landing point of the previous frequency plus or minus the modulo value of the available bandwidth multiplied by 0.618.

The seed for the pseudo-random sequence is the first frequency point of 5.30 MHz, and the step constant is that irrational number.

He quickly pushed the corner of the paper two steps.

当前频率5.35，下一跳：5.35减去0.8乘以0.618再取模后加上基底频率4.8。

The pen tip paused on the paper.

"5.32." He announced the number, his voice just loud enough for Lu Qinghe to hear, below the wind noise. "The next backup frequency band is 5.32 MHz."

Lu Qinghe turned her head and glanced at him.

That glance lasted less than half a second; without asking why, her fingers had already touched the fine-tuning screw of the antenna matching capacitor.

Turn the knob.

The clock hands swung twice.

On the oscilloscope scan line, the 5.32 MHz position was originally covered by a bright interference band. After the difference frequency extraction by DBM-02, an independent narrowband signal emerged from the noise floor.

The white noise in the speaker seemed to be parted by a hand, revealing intermittent ticking sounds underneath.

Lu Qinghe leaned forward two inches, her ear pressed against the edge of the speaker.

Tick-tock, tick-tock, tick.

Her pencil danced across the paper, translating it letter by letter.

"Emergency report from Outpost No. 4." She wrote and read aloud, her voice hoarse from rapid breathing, "A special operations team of twelve men has been spotted, carrying explosive charges, moving along the northeast ditch towards Radar Base No. 3. Coordinates..."

coordinate.

Lu Qinghe read out two sets of numbers, and Jiang Ming grabbed a red pencil from the map and drew an X in the corresponding position.

The fork is located less than two kilometers away from the No. 3 radar base in a straight line.

The canvas curtain was lifted from the outside, and Chen Zhiyuan, his face covered in yellow sand, crawled in, panting heavily.

"The command center is asking if the direction-finding vehicle has received a signal from outpost number four!"

"Received." Lu Qinghe tore off the coordinate slip and handed it over. "The coordinates are on it. Twelve people carrying explosives, target No. 3 base, approaching from the northeast trench."

Chen Zhiyuan grabbed the slip of paper, glanced at the numbers, and turned to run out.

"Wait a minute," Jiang Ming called out to him. "Tell the artillerymen that the spies are moving along the ditch. There are earthen embankments on both sides. It's more effective to hit the ditch entrance with shells than to hit people on the head. The earthen embankments will ricochet off as fragments."

Chen Zhiyuan nodded, bent over, and crawled out of the canvas curtain, disappearing into the sandstorm.

The only sounds inside the carriage were the background noise of the equipment running and the constant howling of the wind outside.

Jiang Ming looked at the clean, narrow-band signal at 5.32 MHz on the oscilloscope and wrote another line on the graph paper with his pencil.

Golden ratio step.

This encoding method is too clean.

It's not something that can be hastily put together on the battlefield.

In the 1930s, the German Navy's communications department used a pseudo-random frequency hopping scheme based on irrational numbers for its stealth radios. The file number was recorded by the Allies when the radios were captured in Berlin after the war.

That scheme has never been publicly released, and there are no more than twenty people in Europe who know the complete algorithm.

The person who guided the implementation of this coding system in the Gobi Desert of Northwest China in 1955 was far more technically skilled than the average intelligence officer.

A muffled boom came from outside the carriage, and the vibrations traveled up from the ground.

The second sound came three seconds later.

Third tone.

Mortar.

Lu Qinghe pressed the earphones back onto her ears, and the knob remained fixed at 5.32 MHz.

The sentry signal from the loudspeaker was interrupted for a few seconds, then reappeared.

This time, it wasn't Morse code that came through, but the voice of a young soldier.

Although the background noise from the interference made the sound intermittent, a few keywords entered the carriage, and each word was clear.

"Hit... at the mouth of the ditch... the explosives detonated... the entire special operations squad was wiped out!"

Lu Qinghe loosened her hand from the knob, spreading her ten fingers outwards as if to loosen her joints, which had become stiff from gripping for too long.

She didn't laugh or say anything; she just rested her head against the iron wall of the instrument rack and closed her eyes for two seconds.

Jiang Ming folded the derivation process on the graph paper and stuffed it into his breast pocket.

The first battle is over.

The frequency hopping pattern has been grasped, and each subsequent hop can be predicted in advance.

But the question mark left in his mind by that golden ratio code was heavier than the answer.

The canvas curtain of the directional vehicle was lifted again.

It wasn't Chen Zhiyuan who came in.

Director Wang stood at the door, his overcoat covered in yellow sand, his hat brim pulled low, one hand holding the hat down, the other holding a square package wrapped in oilcloth.

His face was expressionless under the kerosene lamp; his lips were pressed into a straight line, and his jaw was taut.

"Jiang Ming." His voice was cut in half by the wind, leaving only a harsh tone, "Come with me to the command post."

He lifted the package in his hand.

"Intercepted by the Aksai post office. An hour ago."

Lu Qinghe's gaze fell on the package, her fingers still pressing on the tuning knob, not immediately releasing it.

Jiang Ming pressed the graph paper in his breast pocket further in, then bent down and crawled out of the carriage.

The sandstorm outside had subsided, but as soon as you stepped outside, you could still taste the earthy flavor in your mouth.

Director Wang offered no explanation, but simply walked briskly ahead, his hat brim pressed down.

The lights in the command post flickered through the sand curtain, as if they were about to be blown out by the wind.