Chapter 68: Load and Temperature Rise

21:30. Laboratory. Fluorescent tubes flickering. White light cold. Lin Chen pulled open the drawer of Workbench Three. Took out insulating paper. Smoothed it flat. Spread out the materials. Five two-watt carbon-film resistors. Scraps of aluminum sheet. Copper wire. Thermal grease. A scraper.

He took the vernier caliper. Measured the resistor body diameter. Six point five millimeters. Length fourteen millimeters. He drew a sketch. Parallel. Series. Calculated the equivalent resistance. Target fifty ohms. Power ten watts. Two watts per resistor. Needed five in parallel. Current sharing. Derating factor zero point eight. Actual load capacity eight watts. Two watts of margin. Temperature rise controllable.

He picked up the soldering iron. Plugged it in. Preheated. Rosin-core solder wire. He clipped the leads. Left five millimeters. Set them side by side. Tinned them. Fixed them in place. Movements steady. No shake. The solder joints. Rounded. No sharp tails. All five. Parallel connection complete. Resistance. Forty-nine point eight ohms. Error. Zero point four percent. Within spec.

He took the aluminum sheet. Scissors. Cut it. Length eight centimeters. Width six centimeters. He bent the edges. Ninety degrees. Formed a trough. Fit it against the bottoms of the resistors. He scraped on thermal grease. Thin layer. Even. Coated the aluminum channel. Pressed down the resistors. Copper wire. Wound tight. Bound them. Fixed them in place. The structure took shape.

He connected the multimeter. Checked continuity. The beeper sounded. Resistance. Stable. He connected the DC power supply. Current limit. Zero point five amps. Powered it on. The resistors warmed slightly. The aluminum temperature. Rose. He took the infrared thermometer gun. Aimed it. Reading. Forty-two degrees. Ambient twenty-five degrees. Temperature rise seventeen degrees. Safe.

23:00. Left foot. Gauze. Soaked through. Bloodstains. Dark red. Edges. Hardened. He stopped. Lowered his head. Looked. Did not frown. Took the scissors. Cut open. The old gauze. Peeled it away. The wound. Oozing. Slightly swollen. He took povidone-iodine. Cotton swab. Wiped it clean. The sting. Sharp. He held his breath. Three seconds. Waited for the pain. To ebb.

He took fresh gauze. Folded it. Four layers. Covered the wound. Tape. Secured it. Edges. Smooth. He looked at his watch. Since the last dressing change. Twelve hours. Executed on time. He stood up. Poured water. Washed the cotton swab. The basin. Faintly red. He poured it out. Wiped the work surface dry. No trace left.

00:15. Low-power. Burn-in. Lin Chen connected the signal source. Output. Ten megahertz. Sine wave. Amplitude. Two volts. Connected the load. Power meter. In series. Reading. One point eight watts. Stable. He recorded. Time. Temperature. Resistance. The paper. Flat. The handwriting. Neat.

He leaned back against the chair. Closed his eyes. Breathing. Steady. In his mind. There were no curves. Only thermal resistance. Heat dissipation. Surface area. Current sharing. Three lines. Crossing in the dark. Not colliding. Not tangling. Each of them. Moving forward.

01:30. Powered down. Put everything back. Tools. Cleaned. Graph paper. Bound. First draft of the report. He slung the canvas bag over his shoulder. Went out. Corridor. Empty. Terrazzo. Cold. Wind. Through the hallway. A low whistle. He went downstairs. Stride length. Thirty centimeters. Center of gravity. Shifted right. Did not step. On the frost line.

06:00. Dormitory. Alarm clock. Rang. Lin Chen opened his eyes. Sleep. Four hours. He sat up. Put on his shoes. Tied the laces. Left foot. Touching the ground. The pain. Dull. Bearable. He took the kettle. Drank one mouthful. Cold. His stomach tightened. He took a steamed bun. Half of one. Washed it down with cold water. Carbohydrates. Replenished.

07:15. Laboratory. Door opened. Cold air. Mixed with. The smell of rosin. Old Li. Already standing. At the bench. Military coat. Not taken off. Cuffs. Rolled up. Chen Hao. Across from him. Tuning. A commercial load. Black. Metal casing. Dense cooling fins. Reflective. Cold and hard.

"Begin." Old Li looked at his watch. The second hand returned to zero. "Full-band. Under-load. Testing. Sweep frequency. Ten megahertz. To. Two hundred megahertz. Step size. Ten megahertz. Dwell time. Thirty seconds per point. Record. VSWR. Temperature rise. Power. Fluctuation. If it exceeds spec. Once. Redo it. Absence. Cancellation."

Lin Chen nodded. Stepped forward. Connected the equipment. The load. Inserted into. The RF path. Power meter. In series. Spectrum analyzer. Monitoring. The noise floor. Grounding. Single-point. He powered it on. Preheated. The screen. Lit up. The scan line. Stable.

08:00. Testing. Started. Old Li adjusted the frequency. Ten megahertz. Signal source. Output. Lin Chen looked at the power meter. Reading. Eight point five watts. Stable. He looked at the load. Aluminum sheet. Slightly warm. Infrared gun. Aimed. Forty-eight degrees. Within spec. He recorded. The data.

Thirty seconds. Step to. Twenty megahertz. Thirty megahertz. Forty megahertz. The curve. Smooth. VSWR. One point two. Temperature rise. Rose. Linearly. Fifty-eight degrees. Sixty-two degrees. Sixty-five degrees. Lin Chen’s fingers moved slightly. Adjusted heat dissipation. Fan. Voltage. Five volts. Raised. To. Twelve volts. Airflow. Accelerated. The aluminum temperature. Dropped back. Three degrees.

Over at Chen Hao’s side. The equipment. Alarmed. VSWR. One point five. Over limit. He frowned. Took apart. The load. Retuned. The matching capacitor. His movements. Quick. But. Slightly impatient. Lin Chen’s peripheral vision. Swept over. Did not interfere. Focused. On his own bench.

10:00. One hundred fifty megahertz. Signal source. Output. Power. Nine point two watts. Load. Temperature. Seventy-eight degrees. Critical. Lin Chen stopped. Checked. The drawing. Thermal resistance. Calculation. Margin. Insufficient. He took. Cardboard. Cut. An air guide shroud. Slipped it over. The fan outlet. Aligned it with. The aluminum channel. Airflow. Concentrated. Temperature. Dropped slightly. Seventy-five degrees. Stable.

Old Li made his rounds. Stopped in front of Lin Chen’s bench. Looked. At the screen. Looked. At the load. Looked. At the record sheet. Nodded. "Thermal design. Rough. But. Effective. Continue."

One hundred eighty megahertz. Two hundred megahertz. Sweep finished. Lin Chen powered down. Put everything back. Tools. Graph paper. Bound. Report. Signed. He looked. At the data. Across the full band. VSWR. Below. One point three. Temperature-rise peak. Seventy-nine degrees. Power fluctuation. Less than. Two percent. Within spec.

10:45. Old Li clapped his hands. The whole room stopped. "Testing. Finished. File the data. Provincial competition. Qualification. Final. Confirmation. Next Wednesday. Departure. Venue. Equipment. Checklist. Already sent. Check. The parameters. Any missing items. Fill them in. Yourselves."

The students. Packed up. One after another. Footsteps. Mixed. Chairs. Scraping. Lin Chen. Slung. The canvas bag over his shoulder. Went out. Corridor. Empty. Terrazzo. Cold. He went downstairs. His stride. Unchanged.

11:00. Bulletin board. Crowd. Gathered. Lin Chen stepped forward. Looked. At the provincial competition. Equipment checklist. White paper. Black print. Clear.

Spectrum analyzer. Model. HP8591E. Input. Impedance. Fifty ohms. Maximum. Input. Power. Thirty milliwatts. Front-end. Attenuation. Must be. Set manually.

Lin Chen looked. For three seconds. Did not smile. Did not sigh. Turned around. Left. The crowd. Scattered. Footsteps. Mixed. Wind. Lifted. The corner of the notice. Paper rustling faintly.

11:30. Dorm room. Desktop. Cleared. Lin Chen spread out paper. Drew. Coordinate axes. Horizontal axis. Time. Vertical axis. Parameters. He marked. The provincial competition. Equipment differences. HP8591E. Input attenuation. Step size. Ten. Decibels. Need. A homemade attenuator. Matching. The thirty-milliwatt. Upper limit.

He took. The ledger. Turned to. A blank page. Listed. The checklist.

One. Attenuator. Requires. Precision. Resistor. Network. Tolerance. One percent. Two. Laboratory. Stock. None. Must. Purchase externally. Three. Funds. Remaining. Eighteen yuan nine. Shortfall. Twelve yuan four. Four. Left foot. Wound. Oozing. Need. School hospital. Dressing change. Registration. Five yuan. Medicine. Eight yuan.

He stopped writing. Looked out the window. The sky. Gray and dim. Clouds. Low. Wind. Through. The window crack. A low whine.

He stood. Put on his shoes. Tied the laces. Center of gravity. Shifted right. Stride length. Thirty centimeters. Did not step. In the water stains.

Ahead. The equipment storeroom. Light. Not yet out. Old Zhao. Waiting. For the checklist.

He pushed the door. Open. Went in. Wind. Poured through. Cold.

He closed his eyes. In his mind. There were no curves. Only attenuation. Step size. Impedance. Matching. Three lines. Crossing in the dark. Not colliding. Not tangling. Each of them. Moving forward.

He opened his eyes. Stride length. Thirty centimeters. Did not step. In the water stains.

Forward.