Care and Maintenance
of RF Coaxial Cables for CATV Network
Cable network construction plays an important role in getting
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
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:
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.
Care should be taken while applying force to the cables as excessive
force applied to the cable can cause change in impedance.
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
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.
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.
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.
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.
Cables connection junctions must be protected from moisture and
salt or chemical corrosion. All joints must be sealed properly
with sealant or sealing tape.