Chapter 60: Enameled and Copper-Clad

19:40. Dormitory. Iron bunk bed. Lower berth. Hard wooden board. Covered with old newspapers. Against damp. Lin Chen sat down. Canvas bag. On his knees. The zipper opened. Metal sound. Cold. He took out the components. Enameled wire. 0.08 mm. Carbon-film resistors. 1 MΩ. Ten pieces. Trimmer capacitor. 5–30 pF. Copper-foil tape. Insulating paper. Graph paper. Drafting pencil. Eraser. Ruler. Compass. Arranged them. On the desk. Old. Paint peeling. Wood grain cracked. He counted. Checked. Against the list. No mistakes.

Funds. Eighty-one yuan and five jiao. In the inner pocket. Ledger. Edges curled. He opened it. New page. Date. Time. Task. Parameters. Deadline. Handwriting. Fine. Dense. No cursive.

He pulled out paper. Smoothed it flat. Pinned it with the ruler. Drew coordinates. Horizontal axis. Frequency. Vertical axis. Impedance. Marked the scales. 10 MHz. 10 MΩ. 10 pF. ±5%. He calculated. Distributed capacitance. Probe lead. Coaxial cable. About 80 pF. Needed compensation. Parallel trimmer. Series high resistance. Voltage division. Ratio. Ten to one. Formula. R1 = 9 MΩ. R2 = 1 MΩ. C1. Compensation. C2. Input. Matching condition. R1C1 = R2C2. He listed it out. Calculated. Draft pages. Three sheets. Numbers. Dense. No erasures.

20:15. Winding. Began. He took the carbon-film resistors. Connected nine in series. Total resistance. 9 MΩ. Leads. Cut even. Left two centimeters. Wrapped in insulating paper. To prevent shorts. He took the enameled wire. Wound it. Around the frame. Plastic tube. Inner diameter. Three millimeters. Length. Five centimeters. Wire diameter. 0.08 mm. Tight winding. No overlap. No crossing. One turn. Two turns. Ten turns. Twenty turns. Fingers. Stiff with cold. Joints. Pale. He breathed warm air on them. White mist. Dispersed. Continued. Winding. The wire. Fine. Easy to snap. He controlled. The force. Even. Neither tight nor loose. Fingertips. Feeling. The tension. If it broke. All prior work. Wasted.

Thirty turns. Stop. He measured. Resistance. Multimeter probes. Touched. The leads. Reading. 9.02 MΩ. Error. 0.2%. Acceptable. He connected the trimmer capacitor. In parallel. Bent the leads. Fixed it. Soldering iron. Heated. Rosin. Smoked. Pungent. Fed solder. Withdrew. The joint. Full. No burrs. No cold solder. He measured. Capacitance. Meter reading. Initial. 15 pF. Too high. He turned. The trimmer screw. Resistance. Sticky. He applied force. Extremely light. Half a degree. Stop. Measured. 12 pF. Turned again. 10.5 pF. Stop. Recorded it. On paper.

21:30. PCB layout. Began. He changed paper. One-millimeter grid. Pencil. Sharpened. Drew the frame. Size. Eighty by sixty millimeters. Marked. Connector. BNC socket. Test points. Ground split. He drew the signal trace. Width. 0.5 mm. Impedance control. Fifty ohms. Microstrip calculation. Dielectric constant. Board thickness. Trace width. Spacing. He marked. Parameters. In notes beside it. Ground plane. Solid copper pour. Unbroken. Analog ground. Digital ground. Single-point connection. Avoid loops. Shielding layer. Copper wraparound. Grounded. He drew. The traces. Straight. Corners. Rounded. Used the compass. Drew arc transitions. No sharp angles. To prevent radiation.

22:45. The stabbing pain in his left foot. Worsened. Gauze. Blood seeping through. Dried. Stuck fast. He put down the pencil. Took off his shoe. Sock. Tore it away. Scab. Split open. Deep crack. Edges pale. No pus. He took iodine. Cotton swab. Dabbed it on. Sharp sting. He bit his lip. Made no sound. Waited. For it to dry. Changed. Fresh gauze. Wrapped it. Tight. Not constricting. The bleeding. Stopped. He put his shoe back on. Tied the laces. Tight. Shifted his weight. To the right. Continued. Drawing.

23:20. Schematic. Finished. PCB layout. Finished. He checked the traces. No crossings. No shorts. Impedance. Matched. Ground split. Shielding. Complete. Parameters. Clearly marked. He rolled the drawings. Secured them. Put them. In the inner sleeve. Of the canvas bag. The probe. Packed. Wrapped in electrical tape. Secured. Connector. Tightened. Not loose. He measured. Total resistance. 10.01 MΩ. Total capacitance. 10.2 pF. Error. Plus or minus two percent. Met spec.

01:10. Finished work. He turned off the light. Lay down. Wooden board. Hard. Cold. The air. Sealed still. His breathing. White mist. Dissolved. He closed his eyes. In his head. No curves. Only solder joints. Temperature. Time. Molten solder. Solidifying. Three lines. In the dark. Crossing. Without colliding. Without tangling. Each. Moving forward. He slept. Lightly. Easily woken. No dreams. Only numbers. Jumping.

05:30. Awake. Before the alarm. Body clock. First. He opened his eyes. Ceiling. Water stains. Dried. He turned sideways. Left foot. Tested it. Set it on the floor. The scab. Tightened. Stabbing pain. He paused. Adjusted his breathing. Shifted his weight. Got up. Dressed. Movements. Light. Did not touch. The bed frame. Cold water. On his face. Piercing. He dried off. Changed the dressing. Iodine. Cotton swab. Scab edge. Whitish. No seepage. Wrapped it tight. Put on his shoes. Tied the laces. Canvas bag. Heavy. But steady. Went out.

06:15. Hallway. Empty. Voice-activated light. Broken. Footsteps. On terrazzo. Echoes. Short. Cold. Stride length. Thirty centimeters. Did not step. On the frost lines. Wind. Through the window cracks. Poured in. Low whine. He did not hunch. His shoulders. Breathing. Steady. White mist. Dissolved.

06:55. Laboratory. Iron door. Open. Heating. Not on. Room temperature. Below zero. Group A. Advanced group. Already there. Nine people. Lin Chen. Sat in the corner. Third table. Set down the bag. Opened the case. Probe. Schematic. PCB layout. Arranged them. On the table. Neat. No clutter.

07:00. Old Li. Pushed the door open. Military coat. Collar turned up. Chalk dust. On his shoulders. He knocked. On the blackboard. Three times. The chalk. Snapped. White dust. Drifted down.

“System integration. Prepare. Submit. Drawings. And. Probe. Ten minutes. Check. Parameters. Any out of tolerance. Eliminated. Begin.”

Lin Chen stood up. Handed over the drawings. Flat. No creases. Handed over the probe. Insulation. Intact. Connector. Tight.

Old Li took them. Looked. At the diagram. Traces. Straight. Corners. Rounded. Smooth transitions. Impedance labels. Clear. Ground split. Single-point connection. Shielding. Copper wraparound. He nodded. Neither praised nor criticized. He took. The probe. Measured resistance. Multimeter reading. 10.00 MΩ. Measured capacitance. Meter reading. 10.1 pF. Error. Plus or minus one. Met spec.

“Homemade. Qualified. Sit down. Hook up. The system.”

He turned. Walked. To the lectern. Took. Signal generator. Oscilloscope. IF demodulation board. RF amplifier board. Power module. Arranged them. On the table. Many connections. He drew. A block diagram. On the blackboard. Signal chain. Complete. Closed loop. Input. RF. Amplification. Mixing. Intermediate frequency. Demodulation. Output. Audio. He marked. Test points. Voltage. Waveform. Frequency.

“System integration. Three-hour limit. Goal. Stable gain. Through the signal chain. No self-oscillation. No distortion. Noise. Below five decibels. Instruments. Help yourselves. Parameters. Measure them yourselves. Record. Any excessive error. Eliminated. Probe. Connect. At the input end. Pay attention. Impedance matching. Avoid. Ground loops. Begin.”

The stopwatch. Ticked. Metal casing. Reflecting light.

Lin Chen got to work. Connected the wires. Banana plugs. Inserted. Tight. Not loose. Wire order. Red. Black. No crossing. Power. On. Indicator light. Lit. He connected. The probe. BNC socket. Bit tight. Metal teeth. Locked in. Rubber sleeve. Did not slip. He adjusted. The signal generator. Frequency. 10.7 MHz. Amplitude. 10 mVpp. Waveform. Sine. Stable. He looked. At the oscilloscope. Screen. Green grid. Lit. Waveform. Appeared. Sine wave. No clipping. No distortion. He measured. Gain. Input. 10 mV. Output. 100 mV. Twenty decibels. Met spec.

He measured. Noise. Spectrum analyzer. Baseline. Flat. No stray clutter. Reading. 4.2 decibels. Met spec.

He measured. Phase. X-Y mode. Ellipse. Tilted. Reading. Stable. No drift.

Time. Forty minutes. Left foot. Continued stabbing. Gauze. Slightly damp. Clinging. He ignored it. Shifted weight. To the right. Breathing. Steady. Fingers. Frozen stiff. Joints. Pale. He breathed on them. White mist. Dispersed. Continued. Adjusting. The trimmer potentiometer. Knob. Sticky. He applied force. Evenly. No stripping. Fingertips. Felt. The change in resistance. Half a turn. Stop. Measured. Waveform. Stable. No self-oscillation.

Time. One hour twenty minutes. Chen Hao. Turned in his work. Stood. Left. Footsteps. Light. Confident. Door open. Door shut. Wind. Poured in. Cold.

Lin Chen did not look up. Continued. Retesting. Three sets. Of data. Recorded. Checked. Ran the formulas again. No mistakes. He checked. The wiring. No looseness. No shorts. Probe. Ground clip. Bit tight. Metal. Cold. Shielding. Intact. Ground. Single point. No loop.

Time. Two hours fifty minutes. He put down the pen. Powered off. Removed wires. Tidied. The table. No clutter. Wire ends. Straightened. Instruments. Returned to place. Knobs. Back to zero. Probe. Coiled. Secured.

He stood. Turned in his paper. Flat. Handed it over.

Old Li took it. Looked. At the data. Three sets. Gain. Stable. Noise. Met spec. Phase. No drift. He raised his head. Looked at Lin Chen. Dark circles. Cracked lips. Chilblains. Purpled. But his hands. Steady. No tremor. Under his nails. Rosin. And copper rust.

“How’d you handle the ground?”

“Split. Single-point connection. Avoid loops. Shielding. Copper wraparound. Grounded.”

“How’d you suppress self-oscillation?”

“Added. Bias resistor. Negative feedback. Compensation capacitor. Left enough phase margin.”

Old Li nodded. Neither praised nor criticized. “Sit. Wait for the result.”

The laboratory. Quiet. Only. The low hum. Of instrument cooling fans. In the air. The smell of rosin. Thickened.

Three hours. Up. Old Li collected the papers. Checked them. Scored them. Chalk. On the blackboard. Wrote. The rankings. Handwriting. Heavy. Thick.

Advanced group. Nine people. Lin Chen. First. Chen Hao. Second. Third through ninth. In order.

Old Li turned around. “System integration. Passed. Tomorrow. Enter. Provincial competition simulation. System includes. Full signal chain. And external interference sources. You’ll need. Your own shielding cover. And filter network. Warehouse. Has none. Solve it yourselves. Late arrival. Eliminated.”

He paused. His gaze. Swept over Lin Chen. “Lin Chen. Stay. There’s work.”

The students. Stood. Packed up. Left. Footsteps. Mixed. Door open. Door shut. Wind. Poured in. Cold.

The laboratory. Left with only. Two people. Old Li. Walked to. Lin Chen’s table. Set down. An old signal generator. Casing. Deep scratches. Knob. Loose. Model. Domestic make. Manufactured in 1986. Output. Unstable. Amplitude. Drifting. Frequency. Jumping.

“Old unit. From the provincial team’s discard pile. Old Li says. If you can fix it. Fix it. One machine fixed. Forty yuan. Cash. Paid on the spot. Can’t fix it. Work for nothing. Bring your own tools. Parts. Get them from the storeroom. Time limit. Three hours. Begin.”

Lin Chen looked. At the machine. Reached out. Touched. The casing. Cold. But with. A faint vibration. Powered on. Tested. He did not hesitate. Opened the bag. Took out tools. Screwdriver. Multimeter. Soldering iron. Rosin. Solder. Electrical tape.

He took it apart. Screws. Rusted. Hard to turn. He applied more force. Steady. No slipping. Casing. Opened. Dust. Thick. Circuit board. Yellowed. Solder joints. Oxidized. Blackened. He measured. Power output. Twelve volts. Normal. Amplitude. Drifting. He checked. The zener diode. Aged. Breakdown failure. He desoldered it. Replaced it. Bent the leads. Fixed it. Soldering iron. Heated. Fed solder. Withdrew. The joint. Full. No burrs.

Frequency. Jumping. He adjusted. The crystal oscillator’s load capacitor. Fine-tuned. Compensation. Drift. Knob. Sticky. He applied force. Evenly. No stripping. Screen. Lit. Waveform. Stable. No flicker. He adjusted. The amplitude potentiometer. Knob. Sticky. He applied force. Evenly. No stripping. Output. Stable. No jumping.

Time. Two hours forty minutes. He reassembled. Closed the casing. Tightened. The screws. Powered on. Tested. Signal. Output. Stable. Amplitude. Accurate. Frequency. No jumping.

He stood. Turned in. The machine.

Old Li looked. At the screen. Nodded. “Good. Forty. Cash.” He took out. The money. Bills. Old. But flat. Handed them over.

Lin Chen took it. Stuffed it. Into the pocket. Close to his body. His fingers. Touched. The ledger. Curled edge. Rough paper. Rubbing. Against skin.

Old Li. “Tomorrow. Seven o’clock. Gather in the lab. Simulated provincial competition. External interference source. Already connected. Need. Electromagnetic interference resistance. And power-ripple suppression. Can’t make it work. Eliminated.”

“Understood.”

Lin Chen slung. The canvas bag. Over his back. Went out. Hallway. Empty. Footsteps. Fell on the terrazzo. Echoes. Short. Cold.

He touched. His pocket. Forty yuan. Plus. The previous. Eighty-one yuan and five jiao. Total. One hundred twenty-one yuan and five jiao.

He felt. Neither joy. Nor sorrow. In his head. Only equations. Routes. Countermeasures. Time windows. Physical limits. Three lines. In the dark. Crossing. Without colliding. Without tangling. Each. Moving forward.

He walked. Stride length. Thirty centimeters. Did not step. On the frost lines.

Ahead. Bulletin board. Posted. A new notice. White paper. Black characters. Provincial competition simulation. Deadline. Moved up. To tomorrow. 14:00. External interference sources include. 50 Hz mains frequency. And RF interference. Must independently draw. Filter network. And shielding plan. Submit. By tomorrow morning.

He stopped. Looked. Mains frequency. RF. Filtering. Shielding. He memorized. The parameters. Requirements. Approach.

He turned. Went back to the dormitory. Wind. Passed through. The hallway. Low whine.

He closed his eyes. In his head. No curves. Only solder joints. Temperature. Time. Molten solder. Solidifying. Three lines. In the dark. Crossing. Without colliding. Without tangling. Each. Moving forward.

He opened his eyes. Stride length. Thirty centimeters. Did not step. On the frost lines.

Forward.