A lightning tour of where transmission-line analysis touches everyday systems.
- Wi-Fi and cellular. Every router PCB has microstrip lines from the radio chip to the antenna. The matching networks are stub-or-quarter-wave structures designed to give 50 Ω from chip output to antenna input. Mismatched antenna means halved range, fried PA, or both.
- HDMI and DisplayPort cables. Differential pairs at controlled 100 Ω impedance carry gigabit signals dozens of feet. The connector mechanical design exists in part to maintain that impedance through the mating interface.
- PCIe, USB-C, Thunderbolt. Same story at gigabit-to-tens-of-gigabit speeds. Every gadget that does multi-gigabit I/O is solving impedance, reflection, and crosstalk problems learned in this chapter.
- TV and cable. 75 Ω coax from the curb to your living room. Splitters and amplifiers maintain 75 Ω across the entire distribution.
- Cellular base stations. 50 Ω hardline coax from the cabinet to the antenna up the tower, often with an in-line VSWR-monitoring circulator. A bad antenna or icing on the connector is detected by a rising VSWR alarm.
- Cardiac pacemaker leads are matched transmission lines, inside the body, so that the pacing pulse arrives at the electrode without distortion.
- Test equipment. Every RF connector type (BNC, SMA, N-type, 3.5 mm, 1.85 mm, 1.0 mm) is engineered to maintain 50 Ω across the mating surface, with the bigger, lower-frequency connectors giving way to tinier ones at millimeter-wave frequencies. A scratched SMA connector is a measurable reflection.
- Quartz crystal oscillators. Load capacitors plus the crystal form an LC tank, with their precise values setting the resonant frequency. Cousins of the transmission-line matching network you just learned.