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

The next morning, the cipher machine in the confidential room rang for the third time before stopping.

Just over ten hours after the alert was sent to the Northwest last night, the reply came faster and worse than anyone expected.

The cipher transcribed the last set of numbers, and before his wrists had even recovered from the soreness, he heard someone hurrying down the corridor.

When Wu Hanzhang pushed open the door, Jiang Ming and Fang Xudong had already been waiting inside for ten minutes. The water in the teacups was still hot, and neither of them had touched it.

"Has the telegram arrived?" Wu Hanzhang asked.

The cipher clerk handed over the manuscript paper. Three thin sheets of paper, the blue mimeographed grid densely covered with four-digit numbers and Chinese translations, with a line of words marked in red in the lower right corner of the last page: Urgent, Top Secret, Direct transmission from Northwest Base Direction Finding Station No. 3.

Wu Hanzhang took it and started reading from the beginning. When he got to the middle of the second page, he stopped and stood by the window without moving.

Jiang Ming noticed that the chief engineer tightened his grip on the paper, pressing his knuckles against the edge and crease the thin paper.

"See for yourself."

Wu Hanzhang handed the telegram to Jiang Ming, then turned around and closed the door to the confidential room. He also pulled down the inner panel of the window to block the view from the corridor.

The telegram began with the sender's name: Lu Qinghe, technician on duty at Direction Finding Station No. 3.

The first paragraph of the main text states: Since September 27, a new type of high-frequency sweeping interference has appeared in the direction of the Altun Mountains. The operating frequency band is 5.2MHz to 5.4MHz, the peak power is estimated to be no less than 1 kilowatt, and the sweeping rate is extremely high, covering the entire 200 kilohertz bandwidth no less than three times per second.

Second paragraph: The antenna of the shortwave walkie-talkie at the front-line patrol post was severely overloaded with spurious signals. The grid of the triode at the front end of the receiver was driven into the cutoff zone, and all frequency communications were interrupted. The patrol team had lost contact with the command post for more than 36 hours.

The third stage: Intermodulation distortion occurs in the front-end circuit of the main receiver of the direction-finding outpost. Strong interference signals generate a large number of combined frequency components in the front-end mixer stage. The effective signal is submerged in the intermodulation products, making it impossible to identify any azimuth information, and the direction-finding function is completely lost.

The fourth paragraph states that the jamming not only covers the shortwave communication band, but also detected intermittent pulsed spurious radiation in the centimeter-wave radar test band from 4.9 GHz to 5.1 GHz, suggesting that the enemy is debugging a second jamming device.

The fifth and final paragraph states: The frontline urgently needs Beijing to provide anti-jamming receiving front-end solutions and centimeter-wave microwave source countermeasures; otherwise, the encirclement and mopping-up troops will completely lose their sight and hearing in the desert. Please reply immediately.

At the end of the telegram was a note, the handwriting of which was noticeably more illegible than the main text: This telegram was subjected to strong interference during transmission and was successfully retransmitted three times. The output power of the transmitter has been set to the maximum, and it cannot be guaranteed that communication can be maintained in the future.

Jiang Ming read the telegram again from beginning to end, his gaze finally settling on those four words in the third paragraph.

Intermodulation distortion.

Fang Xudong, standing behind him, also saw it. He pointed to the paper, his voice low: "When a peak power of one kilowatt hits the walkie-talkie antenna, the front-end triode will naturally be pushed into the high-signal region. The third-order intermodulation products will fall directly into the passband; this is not a problem that tuning can solve."

Jiang Ming placed the telegram on the table and gently smoothed out the creases with his palm.

On the paper, the three characters "Lu Qinghe" are framed by mimeographed grids, and the strokes appear to be taut from the rapid printing.

He stared at the name for two seconds before speaking.

"The front-end mixer of a typical superheterodyne receiver is a single-ended structure, and there are no means to suppress local oscillator leakage and signal intermodulation. When strong interference comes in, the third-order product is larger than the useful signal, and the receiver is just a piece of scrap metal."

Wu Hanzhang leaned against the window, arms crossed: "You mean change the mixer structure?"

"It's not about replacing it." Jiang Ming took a pencil out of his pocket and drew a square on the blank space on the back of the telegram. Inside the square, he wrote four words: "It's about redoing it."

The four words are: dual-balanced mixing.

Fang Xudong leaned closer to take a look at the cube, his brows furrowing: "A dual-balanced mixer requires four mixer diodes with perfectly matched characteristics, as well as a broadband balun transformer, which is not available in China."

"If you don't have it, then do it."

Jiang Ming tapped the tip of his pencil on the last line of the telegram's notes. Lu Qinghe said it only succeeded after three resends, and the telegraph machine's output power was already set to maximum.

This is not a typical fault report.

This is a distress call that the direction finding station managed to squeeze out from the edge of interference. Whether the next one will be able to be sent is anyone's guess.

"She said," Jiang Ming looked up, "that follow-up communication cannot be guaranteed."

Upon hearing this, Wu Hanzhang remained silent for a few seconds, then walked back to the table from the window, picked up the last page of the telegram, flipped it to the back, and looked at the square drawn by Jiang Ming.

How much intermodulation can a double-balanced mixer suppress?

"Theoretically, odd-order intermodulation products and local oscillator leakage are simultaneously canceled by the balanced bridge circuit, and the third-order intermodulation suppression ratio is at least 20 to 30 decibels higher than that of the single-ended structure."

"Twenty to thirty decibels." Fang Xudong repeated the number, his lips moved slightly, but he did not object further.

Wu Hanzhang put the telegram back into the envelope, signed his name and the date on the seal, handed it to the telegraph operator to lock in the safe, and then turned to Jiang Ming: "Make a list of what you need and send it to my desk before this afternoon."

Jiang Ming had already mentally analyzed the entire technology chain from beginning to end.

A dual-balanced mixer requires two core components: a local oscillator that can operate stably in the gigahertz frequency band, and four mixer diodes with extremely small junction capacitances and as closely matched characteristics as possible.

The core of a local oscillator is a high-frequency triode. These are not currently available in China.

Mixer diodes require junction capacitances as low as the picofarad level. There are none available domestically.

Neither.

Both have to be done from scratch.

"Three days." Jiang Ming put the pencil back in his pocket. "Give me three days."

Wu Hanzhang didn't ask if three days was enough; he simply nodded, opened the door, and went out.

Only Jiang Ming and Fang Xudong remained in the confidential room. The clock on the wall struck 10:20, and outside the window, someone was moving oxygen cylinders in the courtyard, the metal cylinders clanging together with a dull thud.

Fang Xudong put his hands back in his white coat pockets and looked at Jiang Ming's profile: "I can understand a dual-balanced mixer, but what about the local oscillator? The silicon transistors sent by the Institute of Physics lose gain above 500 MHz. What are you planning to do?"

Jiang Ming did not answer.

He was still looking at the square he had drawn on the back of the telegram. The pencil lines were light, but the four characters were written with great force.

Intermodulation distortion means that Lu Qinghe's direction finding station has gone blind, the encircling forces have lost contact in the desert, and the enemy is still debugging the second piece of equipment.

Three days, seventy-two hours.

He had to create two things from scratch, things that no one had ever made on this land before.