Description: 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 stand-mounted or hand-held video camera to project a magnified image onto a video monitor 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. 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 low 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 capacitance, 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 higher velocity of propagation. This results is a cable with low-loss characteristics and reduced attenuation of the signal. To improve the electrical properties even further, a gas injected foamed composition of these materials is recommended.
A Braided Shield is the proper type o shield for CCTV and has two key purposes. One is to provide a low D.C resistance grould 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 acceptable 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 cooper braid is still used to provide the low D.C.R return path.
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 low 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 capacitance, 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 higher velocity of propagation. This results is a cable with low-loss characteristics and reduced attenuation of the signal. To improve the electrical properties even further, a gas injected foamed composition of these materials is recommended.
A Braided Shield is the proper type o shield for CCTV and has two key purposes. One is to provide a low D.C resistance grould 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 acceptable 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 cooper braid is still used to provide the low D.C.R return path.
