Send a signal down a long cable and it gets weaker. That is attenuation — the loss of signal strength during transmission. It happens in copper, fiber, and free space. The longer the distance, the greater the loss. Frequency matters too. Higher frequencies attenuate faster than lower ones.

Attenuation is measured in decibels. A loss of 3 dB means half the power is gone. A loss of 10 dB means one tenth remains. Engineers calculate link budgets to ensure the signal arrives strong enough to be detected. If it does not, they add amplifiers or repeaters.

Causes of attenuation

• Resistance in copper conductors
• Absorption and scattering in fiber
• Free space path loss in radio
• Connectors and splices
• Water in cables and poor shielding

Attenuation limits how far signals can travel. DSL works over a few kilometers of copper. Fiber needs amplifiers every 50 to 100 kilometers. Wi-Fi covers a home or office. The physical world imposes limits that no amount of engineering can fully overcome.