CCTV SYSTEMS CCTV cables
CCTV SYSTEMS • Cable selection is a very important consideration in the performance of a CCTV system, especially where long distances need to be addressed. • We will start with the low quality choices that are typically part of an out of the box solution and move through the cable hierarchy.
CCTV SYSTEMS • As mentioned in an earlier lecture composite cables are usually bundled with low cost systems. • In the world of video composite cables consist of a red, white and yellow lead with RCA ends. The red and white cables are your right and left audio cables, respectively. The yellow is a composite video cable.
CCTV SYSTEMS • For CCTV applications the red lead is power, the yellow lead provides the video feed and the white lead is for audio if applicable. • Because these cables are premade it is important to make sure the red male lead is installed at the camera end.
CCTV SYSTEMS • Composite cables are thin gauge and generally only good for 100 to 200 feet. • These cables are also easily susceptible to damage if not installed carefully and they do not provide much protection from EMI (electro magnetic interference) or RFI (radio frequency interference).
CCTV SYSTEMS • Two sets of pre terminated composite cables can be connected together with barrel connectors. • If the RCA ends break off you will have to solder on new ones which is a time consuming process.
CCTV SYSTEMS • Coax has historically been the cable of choice for CCTV systems, RG-59U being the most commonly used type of coax. • Its important to understand the construction of coax cable, almost all coax types are constructed in a similar fashion with very few exceptions.
CCTV SYSTEMS • Here are the 4 parts of a coax cable, the foil shield and braid are considered to be the same and they serve the same function.
CCTV SYSTEMS • What do you think is the primary function of the braid/shield of a coax cable is for? • The braid is grounded at the equipment (technical ground) and serves to discharge any induced EMI. To control EMI and RFI
CCTV SYSTEMS • RG-59U is what the majority of CCTV installations utilize and can be ordered with two 18 gauge conductors for power. • These are called siamese cables the two 18AWG are bonded to the jacket of the RG-59 cable. ONE OF THE SPECIFICATIONS FOR CCTV IS A COPPER BRAID
CCTV SYSTEMS • RG-59U is terminated with BNC (bayonet Neil Councelman) connectors which are a twist and lock style connector with a separate bayonet that covers the center conductor of the coax cable. COMPRESSION CRIMP TWIST ON
CCTV SYSTEMS • Today compression fittings are the most popular and commonly used types of connectors in the industry. • It is important to not allow any strand of the braid to come in contact with the center conductor when terminating fittings onto coax. BNC COMPRESSION FITTING COMPRESSION TOOL
CCTV SYSTEMS • RG-59 is usually specified for 750 to 1000’ feet, beyond this limit the video resolution will start to degrade especially in color systems that operate at higher frequencies. • To overcome this distance limitation we would step up to the next higher grade and gauge coax which is RG-6U sometimes referred to as “series 6”.
CCTV SYSTEMS • When specifying BNC connectors it is important to get connectors for specific cable types, RG-59 BNCs will not work on RG-6 cable and vice versa. • RG-6 can be installed upwards to 1500 feet before we would need to move up to the next grade of cable.
CCTV SYSTEMS • We can increase the length of the RG-59 and RG-6 cables by installing video amplifiers, these devices can double the length of the cable runs.
CCTV SYSTEMS • RG-11 would be the next logical choice since it is a thicker coax cable essentially providing lower loss over longer distances. • RG-11 is rarely used, instead video amplifiers would be installed, for distances of several miles RG-11 still would not be applicable. • Any idea what cable would be used where distances are measured in miles?
CCTV SYSTEMS • Optical fiber would be used for very long distances. • A fiber to coax transceiver (media converter) would be required to convert the video signal to be accept by the camera and DVR. • The DOT cameras are all connected by fiber optics.
CCTV SYSTEMS • Many of the newer CCTV systems are designed for UTP (unshielded twisted pair) which means that the existing infrastructure of network cabling can be utilized. • Cameras can be ordered with RJ-45 ports to accept twisted pair cabling.
CCTV SYSTEMS • When using UTP (CAT 5e/6) for camera installs, what is the distance limitations? • These types of cameras will generally be plugged into a PoE (power over Ethernet) switch that can provide remote power to the camera. 328 feet or 100 meters which is the full channel length.
CCTV SYSTEMS • So the bottom line is that RG-59U is the cable that is most likely to be used for the CCTV install. • The impedance of RG-59, RG-6 and RG-11 is 75Ω. • There are some basic cabling standards associated with installing any type of coax cable.
CCTV SYSTEMS • The pulling force for coax is 35 foot pounds. • The bend radius for coax is 10 times the diameter. • The cable quality is dependent on the precision and uniformity of the center core, dielectric and the braid/shield.
CCTV SYSTEMS • Sharp bends and tight loops affect the cable uniformity and consequently the impedance which results in high frequency losses and image reflections.
CCTV SYSTEMS • When using siamese coax cable the two 18 gauge conductors will be terminated with spade style electrical connectors since these will terminate onto screw terminals.