By James Reinholm
Although most people probably haven’t given it much thought, the invention of the coaxial cable was probably one of the most important discoveries ever made. Telecommunications and radio broadcasting would not exist as they are today without the invention of the coaxial cable.
Coaxial cables first started to appear in various applications back in the 30’s as a need developed for more efficient cabling systems with less interference. As more coaxial cables were used, standardised versions became available. Probably the most important parameter used in coaxial cabling is the characteristic impedance.
This is the main electrical characteristic that determines the level of power transfer and attenuation along the cable length, and also controls the amount of reflected and standing waves. Any type of coaxial cable is typically chosen based on the characteristic impedance. The main consideration is that impedance levels should match both at the transmitting and receiving end.
Although there are many standard impedances levels, the most common ones by far are the 50Ω and 75Ω impedances. These two standards are used for most coaxial cable applications, but other standards are also available in lesser quantities. For ordinary signal and data transmission applications, the cable that almost always chosen is the 50Ω type, while the 75Ω type is almost exclusively used for video signal and high-frequency RF applications, such as VHF (Very High Frequency) and UHF (Ultra High Frequency).