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Technical Support


CCTV Coaxial Cable (1)

ความรู้สนับสนุนด้านเทคนิค : CCTV Coaxial Cable (1)

LENSO: CCTV Coaxial Cable (1)

Standard Analog Video Cable

Closed circuit simply means that the signal is not
being broadcast any where, but rather is traveling
by wire from the source to the receiver.
Usually a closed-circuit television (CCTV) system
uses a
standmounted or hand-held video camera
to project a magnified image onto a video moniter
or a television (TV) screen. Traditionally video
transmission in CCTV is done using 75 ohm coaxial
cables. The video signal transmitted is generally
normal composite video signal, although some
systems use RF signals. A CCTV video signal is
comprised of both low frequency components
(horizontal and vertical sync pulse information)
and high frequency components (video information).
In order to transmit this full spectrum of frequencies
with little distortion or attenuation, it is important
to select the correct coaxial cable that meets the
specifications for
CCTV transmission.

Center Conductor material made of bare copper
is recommended
for optimum performance in CCTV
signal transmission. Because
a CCTV video signal
is a base-band composite video with fairly
frequency components compared to a CATV RF
signal, the
low D.C. resistance that copper provides
will greatly improve the
video signal transmission.

Dielectric Material of a coax cable is also another
key area that
should be addressed. The dielectric
material and it’s composition
is critical as it sets up
the electrical characteristics such as
velocity of propagation, impedance, and attenuation
of the cable. These parameters will determine signal
strength and
transmission distance. It is recommended
to choose a dielectric with
excellent electrical properties
such as polyethylene or
Foam PE.
Such material will
give you lower capacitance and a higher velocity
propagation. This results in a cable with low-loss
and reduced attenuation of the signal.
To improve the electrical
properties even further, a gas
injected foamed composition of these
is recommended.

A Braided Shield is the proper type of shield for
CCTV and has two
key purposes. One is to provide
a low D.C. resistance ground path
and the second
is to provide shielding of outside interference from
distorting the video signal. The shielding should be
constructed of
bare copper to provide a low D.C.R.
return path. It should have a 95% or better braid
coverage in order to provide adequate shielding from
outside electrical interferences. Anything less is usually
not acceotabke for CCTV. To provide increased shielding
in the RFI range, a construction of an aluminum foil tape
is acceptable as long as a high percentage copper braid
is still used to provide the low D.C.R. return path.


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