lossy

In electrical engineering, a lossy channel or medium is one where electromagnetic energy is converted into heat rather than being transmitted intact. This happens because real conductors have resistance, dielectrics absorb energy, and free space itself can scatter or attenuate waves. The result is measurable degradation: signal amplitude decreases with distance, bandwidth narrows, and noise floor rises relative to the useful signal.

Common examples include twisted-pair copper cabling, coaxial cable, and radio propagation through buildings or dense atmosphere. A 100 meter run of Cat5e at 1 MHz might lose 2 decibels; at 100 MHz it loses far more. Fiber optic cable is much lower loss, typically 0.2 to 0.5 dB per kilometer in the infrared bands used for telecommunications, but it still loses energy. Even air transmission of radio waves follows an inverse-square law: power density drops as distance squared from the antenna.

The opposite is a lossless channel, a theoretical abstraction. Real transmission lines and channels are always lossy. Engineers compensate by using amplifiers, equalizers, and error correction codes. In high-speed digital signaling over copper, loss becomes severe above a few gigahertz, which is why servers use fiber optic interconnects for distances beyond a few meters.

Loss is quantified in decibels per unit length, per unit frequency, or per unit distance depending on context. Microwave engineers specify loss tangent or dissipation factor for dielectric materials. Signal integrity teams model lossy transmission line effects using distributed RC parameters or full Maxwell solvers. A PCB trace carrying a 10 GHz signal must account for dielectric loss, conductor loss, and radiation loss or the signal will be unrecognizable at the receiver.