Coax Cabling: RG6
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.
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