Video coaxial cable is designed to transmit maximum
signalling energy from a 75ohm source to a 75ohm load
with minimum signal loss. Excessive signal loss and
reflection  occurs
if cable rated for other than 75ohms is used. Cable
characteristics are determined by a number of factors
(core material, dielectric material and shield construction,
among others) and must be carefully matched to the
specific application.
In the average CCTV installation, with cable lengths
of less than 750 feet (228 m), RG59/U cable is a good
choice having an outside dimension of approximately
0.25 inches. For short cable runs, use RG59/U with
a 22-gauge centre conductor, which has a DC resistance
of about 16 ohms per 1,000 feet (304 m). For longer
runs, the 20-gauge variety, which has a DC resistance
of approximately 10 ohms per 1,000 feet, will work
well. For installations requiring cable runs between
800 (244 m) and 1,500 feet (457 m), RG6/U is best.
Due to its large-diameter centre conductor of about
18 gauge, RG6/ U has a DC resistance of approximately
8 ohms per 1,000 feet (304 m) and can deliver a signal
farther than RG59/U. Use RG11/U to exceed the capability
of RG6/U. Following is the table showing the maximum
distances for different type of cables.
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