Coaxial cables carry a nominal impedance of between 35 and 185 ohms. The three most common coax cables are 50 ohms (most widely used in thin-net Ethernet), 75 ohms (the cable your most likely using at home for your TV or cable modem) and 93 ohms, which is rarely used.
Coax cable can support much higher bandwidths than unshielded twisted pair (UTP) cable. The most efficient transfer of energy, over coax, occurs when all parts of the system have the same impedance. For example, a transmitter, interconnecting cable, and receiver should all have matching impedance. This need for impedance matching is especially critical at higher frequencies, where the consequences of mismatches are more severe.
Knowing how to install and terminate coax cable properly is critical to achieving impedance matching. Knowledge and selection of the best available materials greatly increases efficiency.
The most common type of coax, called Flexible Coax, is a flexible cable, which uses a braided shield of extremely fine wires. This braid helps to make the coax flexible, but at a cost: energy or RF (radio frequency) signals leak through the small gaps in the braid. To combat this attenuation (energy loss), manufacturers have added several layers of braid and placed thin foil between the layers. This provides better coverage for greater shielding effectiveness. We normally use a quad shield (two layers of braid, two of foil) for 75-ohm applications.
Even though coax makes up a small percentage of our total installations, it is still a critical piece of the infrastructure puzzle for our customers. Coax has been the medium of choice for high fidelity audio, television, satellite and broadband communications.
