Standard Analog Video Cable
Jacket Choice is mainly determined by the
environment where the cable will be installed.
The cable jacket provides two major functions.
One is to provide protection from the elements
a cable may be subjected to, and the second
is to provide solid termination. PVC is a good
choice for most applications inside buildings.
Polyethylene is recommended for outdoor
applications where the cable may be subjected
to the elements and a high degree of moisture,
sunlight, and where abrasion resistance is required.
Do not install indoor rated cable in aerial, direct
burial or underground pipe. An indoor rated cable
is not designed for these harsh environments and
the electrical and mechanical characteristics will
degrade over a period of time and will need to be
replaced. Always follow the NEC code for the proper
cable type for your installation.
Coaxial Cable Parameters vary depending on the
type of coax construction. All coax cables have a
characteristic impedance. The impedance of CCTV
equipment is 75 ohms; therefore, in order to have
minimum losses, it is important to choose a cable
with a matching impedance of 75 ohms. If a coax
cable of another impedance (50 ohm or 93 ohm)
is chosen, then you will experience signal loss and
reflections resulting in short distance transmission
and poor picture quality. Coaxial cables are also
available in different RG types. RG stands for Radio
Guide and is a term that is used when sending Radio
Frequency (RF) signals down a coaxial cable. 75 ohm
coaxial cable comes in several sizes with the most
common types being RG-59, RG-6 and RG-11.
An RG-59 cable is the most commonly used coax
because it is small in diameter and easy to work
with. The RG-11 cable is the largest in diameter
and harder to work with. The RG-6 is between the
two. The difference between the RG types is not
just size, but also the attenuation characteristics
and therefore the transmission distance.
Installation Considerations
Indoor Environments are the most common for
coaxial cable installations. A few tips on installing
coaxial cable are as follows:
1. First and foremost, follow all NEC requirements
when installing coaxial cables.
2. Distribute the pulling tension evenly over the
cable and do not exceed the minimum bend
radius Exceeding the maximum pull tension
or minimum bend radius of a cable can cause
permanent damage both mechanically and
electrically to the cable.
3. When pulling cable through conduit, clean the
conduit completely and use proper lubricants
in long runs.
Outdoor Installations require special installation
techniques that will enable the cable to withstand
harsh environments. When using cable in an aerial
application, lash the cable to a steel messenger wire.
This will help support the cable and reduce the stress
on the cable during wind, snow, and ice storms.
When direct burying a cable, lay the cable without
tension so it will not be stressed when earth is packed
around it. When burying in rocky soil, fill the trench
with sand. Lay the cable and then place pressure-treated
wood or metal plates over the cable. This will prevent
damage to the cable from rocky soil setting. In cold
climate areas, bury the cable below the frost line.