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

When Lu Qinghe wrote down the start and end times, frequency offset, and amplitude characteristics of the eight-second carrier wave into his notebook, his wrist was as steady as if he were holding an optical instrument.

That was the second abnormal carrier wave that appeared in the evening, exactly the same as the one at 5 p.m., lasting for eight seconds, with a frequency offset of 1.2 kilohertz, and no keying interrupt.

Chen Zhiyuan had already stood behind her, bending over to look at the afterglow of the waveform that had just disappeared on the oscilloscope screen.

"The frequency is 1.2 kilohertz higher than the normal signal, and the amplitude is about the same as usual, but there is no key interruption at all." Lu Qinghe closed the pen cap and turned the notebook towards him.

"Same as this morning." Chen Zhiyuan flipped to the record from 5 p.m. for comparison. "The frequency offset, duration, and amplitude characteristics all match."

He drew a line between the two records and wrote a question mark next to it.

"Notify the command post." Lu Qinghe stood up.

Old Zhou picked up the phone, cranked the generator twice, and reported the abnormal signal characteristics.

Through the receiver, the duty officer repeated and confirmed, saying, "Recorded, action plan unchanged, continue monitoring at the direction finding point."

After hanging up the phone, Lao Zhou rubbed his hands and returned to the stove deep inside the wooden house.

"It doesn't affect operations, but what exactly is this signal?"

No one answered.

Lu Qinghe sat back down in front of the receiver and adjusted the oscilloscope's time base knob to a slower scan speed.

This way, if the eight-second carrier wave reappears, she can see more complete waveform details on the screen.

At 9 p.m., the enemy radio station resumed its regular "three short, one long, three short" radio transmission, with a 12-second interval, which was 3 seconds shorter than in the afternoon.

At 10 o'clock, the interval was reduced to ten seconds.

At eleven o'clock, Lu Qinghe's alarm clock rang.

She turned off the alarm and began the final round of equipment checks.

The emission current of the A02 was 148 microamps, which was four points lower than in the afternoon.

The white paint markings on the delay line secondary capacitors are not offset.

The oscilloscope is focused correctly.

The spare tube A03 quietly glowed its filament on the preheating stand next to the shockproof box, its dark red light reflecting on the wooden wall like a motionless firefly.

At 11:45, Chen Zhiyuan brought in a kettle of boiling water from outside and filled all three enamel mugs.

"Fifteen minutes until midnight." He placed his tank next to the delay line control position and rubbed his frozen fingers.

Lu Qinghe didn't drink any water; her attention was entirely focused on the oscilloscope screen.

At 11:57, the last set of "three short, one long, three short" streaks swept across the screen, the delay line pressing it down into a small clump of almost invisible residual spikes.

The compass line still points to the depression in the eastern section of the Camel Trail.

It's exactly twelve o'clock.

No sound could reach them from the distant Gobi Desert. The encirclement troops set off in radio silence, and the signal flares would not be launched until the designated time.

Inside the wooden house at the second direction finding point, only the equipment was in operation.

At 12:15, the enemy station sent a pulse signal, with an interval of nine seconds.

At 12:24, another group started, with a nine-second interval.

The orientation remains unchanged.

Lu Qinghe checks the ammeter of Jia Ling Er every fifteen minutes.

At 12:15, 146 microamps.

At 12:30, 145 microamps.

At 00:45, 143 microamps.

The slope of the descent curve is steeper than during the day. At night, the temperature drops to minus 22 degrees Celsius, the heat dissipation of the tube shell accelerates, the thermal equilibrium point of the filament shifts downward, and the emission efficiency of the coating also decreases.

At 1:00 AM sharp, enemy radio suddenly fired three sets of "three short, one long, and three short" signals in quick succession, with a nine-second interval, followed by silence.

Lu Qinghe waited for thirty seconds, but there was no fourth group.

Another thirty seconds passed, and still nothing.

She reported to the command post: "Target has not moved, signal paused."

At 1:30 a.m., the enemy station resumed operation, fired two sets of signals, and then went silent again, with the silence lasting for four minutes.

"I'm hesitating," Chen Zhiyuan said in a low voice.

Lu Qinghe did not respond to his judgment, but only recorded the exact time of each telegram and silence in her notebook.

At 2 a.m., the current of the Jia-02 circuit dropped to 140 microamps.

She stood up and walked to the shockproof box, took out the Jialingsan lamp and placed it on the spare socket. After confirming that the filament was preheated and stable, she wrote a line in the blank space of the notebook: 140 microamps, switch after another 20 microamps.

As she returned to the operating position, her gaze inadvertently swept across the oscilloscope screen.

After a brief silence at the baseline, a waveform slowly rose.

Eight-second continuous carrier wave, third time.

The frequency is still 1.2 kHz higher than the calibrated value, the amplitude is stable, and there is no keying interruption.

But this time, Chen Zhiyuan made a move.

He turned the oscilloscope's time base to the fastest setting, stretching the eight-second carrier wave into an extremely long bright line on the screen, magnifying every detail to the point of visibility.

The carrier surface is not smooth.

There is a very shallow undulation superimposed on the main waveform, with an amplitude of only about two percent of the main signal.

If the delay line hadn't filtered out all the reflected noise first, this tiny amplitude modulation would have been completely buried under the noise and invisible.

"There's something there." Chen Zhiyuan's voice was very low, as if he was afraid of disturbing the fragile evidence on the screen.

Lu Qinghe leaned over to look for three seconds, then stepped back so as not to block his view.

"Subcarrier amplitude modulation, the frequency is about two to three kilohertz higher than the main carrier, and the amplitude is about two percent." Chen Zhiyuan estimated while recording in his notebook. His handwriting was messy but the data was accurate, and he drew a question mark at the end.

"What's this?" Old Zhou walked over from the stove.

"Uncertain." Chen Zhiyuan closed his notebook. "It could be misleading data, or it could be intentionally added extra information."

"If it's information, it's much more covert than a normal telegram." Lu Qinghe said this and didn't elaborate further.

She wasn't a codebreaker; her job was to provide orientation guidance.

But she noted this discovery down in the list of items to be reported.

At 2:40 a.m., after the eight-second carrier wave disappeared, the enemy station fell silent again.

At 2:50, a sequence of "three short, one long, and three short" flashed across the screen, with an interval of nine seconds.

The location hasn't changed.

After recording the data, Lu Qinghe glanced at the ammeter.

136 micro-amperes.

The 02A tank is still holding on, but only 16 microamps remain.

She set the alarm to 3:15, and if the current drops below 130 microamps at that time, she will switch it.

At 3:02 a.m., the last set of "three short beeps, one long beep, and three short beeps" left a residual image on the oscilloscope.

The delay line was still flattened, and the orientation data showed no abnormalities.

At 3:03, the screen went silent.

At 3:04, it was still quiet.

Lu Qinghe rested her hand on the pen, her gaze fixed on the baseline.

Five past three.

The communications team's duty officer pushed open the door from the outside and handed Lao Zhou a note.

"All units report that they have reached their designated positions and are awaiting the signal flare."

Old Zhou nodded and took the note, preparing to reply.

Lu Qinghe suddenly spoke, her voice not loud, but it drew everyone's attention.

"The signal is gone."

On the oscilloscope screen, there was only a single, unchanging green baseline, and even the thermal noise spikes were less noticeable than three minutes ago.

Because the radio frequency source that once existed has now been uprooted from the air.

The ammeter pointer on the Jialing 2 still pointed to 136 microamps; the tube was still alive, and the receiver was still working.

But there is no signal to receive anymore.

Before the encirclement could even begin, the enemy's communication tower went out first.