Koaksiaalijohdot

Koaksiaalijohdot, commonly known as coaxial cables, are transmission lines composed of an inner conductor, a dielectric insulator, an outer conductive shield, and an insulating jacket. The inner conductor carries the signal, while the shield provides electromagnetic interference (EMI) protection and acts as a return path. The dielectric maintains a constant electrical spacing, enabling a stable characteristic impedance typically around 50 or 75 ohms.

These cables are widely used for cable television, broadband internet, security systems, and radio frequency (RF) communications because they combine low signal loss with robust shielding. The 75-ohm variant is standard for high‑definition video and cable TV distribution, whereas the 50-ohm variant is common in RF transmission and telecommunications. Coaxial cables are rated for frequencies ranging from a few megahertz up to several gigahertz, depending on construction and shielding quality.

Standardized types include RG‑6, RG‑58, and RG‑141, each specified by the American Wire Gauge (AWG) system for core diameter and impedance. In Europe, categories such as RG‑8 and 0G are also prevalent. Coaxial cable design parameters—core size, dielectric material, and shield type (screened or braided)—directly influence attenuation, return loss, and frequency limits.

Historically, coaxial cables originated in the early 20th century and have evolved through improvements in materials and manufacturing techniques. Modern variants employ polyethylene, PTFE, or foam dielectrics to reduce loss. Despite their advantages, coaxial cables can be more expensive and less flexible than twisted‑pair cabling, and they require careful handling to avoid kinks that may distort impedance. Field installation typically involves connectors such as BNC, F‑type, or 75‑ohm RJ‑45, with meticulous performance testing to ensure signal integrity over cable runs.