Care and Maintenance of RF Coaxial Cables for CATV Network

Cable network construction plays an important role in getting  clear   and
uniterrupted distribution of signals.The cable should not be tied to trees, poles etc, which can lead to damage of cables.We must try to do the best under the existing conditions of legal sanctions and environment so that our subscribers get clear & uninterrupted distribution.

Trunk Distribution Cable
In a large network thicker cables, e.g., B-120 (500 series) and B-90 (475 series) are used for trunk and distribution but in small networks operators use B-70 (equipment RG-11) as a trunk.

Some important points to remember while laying these cables are:

Support Cables
A steel messenger wire insulated with P.V.C or P.E. must be used for supporting the main cable. A naked support cable or tight lashing of support cable should be avoided.

Pulling Tension
Care should be taken while applying force to the cables as excessive force applied to the cable can cause change in impedance.

Bending Radius
Bending of cables around corners should be proper so as not to damage the cable. The static bending radius is the minimum-bending radius up to which a cable can be bent without electrical or mechanical degradation.

Expansion Loops
All metals expand due to rise in temperature. The difference between the expansion and contraction coefficients of the support wire and the coaxial cable is accounted for by using expansion loops to allow movement of the coaxial cable in relation to the support wire. If expansion loop are not catered for, suck-outs may occur at the joints, which may result in the center conductor coming out of the amplifier or tap-off socket, causing snowy picture.

Excess Cable Loops
A few extra cable loops must be made at some selected points so that, in case of slight change in route or cable cutting, this excess cable can be utilized.

Drop Installation
This is the installation of drop cable, e.g., RG-59, LCG-21, B-40 from the tap off to the subscriber’s TV set. During installation the cable should not be bent so tightly that the stiffer inner conductor is forced against the softer foamed polyethylene. Excessive force can result in impedance drop causing signal reflections.

Grouping of Drop Cables
To protect the subscriber’s home, drop cables are always grouped through the use of a ground, usually a metallic pipe that is known to run at least 10 ft through the earth.

Sealing of Joints
Cables connection junctions must be protected from moisture and salt or chemical corrosion. All joints must be sealed properly with sealant or sealing tape.


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