A complete CCTV setup involves different components, including the camera, monitor, recording device, power supply, cables, and connectors. Every component must be high-quality for the best results.
A coaxial cable for CCTV consists of different layers of various materials wrapped on top of each other. If you look at the cross-section of the cable, you’ll see in the middle is a metal wire conductor that carries the signal. Over this is a dielectric material, a braided sheath, and then an insulating jacket.
Each layer must be made of a suitable material and properties to provide the best output. Furthermore, it’s essential to consider characteristics like impedance and RG type when choosing the cable. Let’s take a look at each of these parameters.
Central conducting wire
At the centre of every coaxial cable is a conducting metal wire. Usually it is made of pure copper or copper-covered steel. However, for CCTV applications, any CCTV expert will recommend the former as it offers better signal transmission for high-frequency video components. Copper-covered steel is more suitable for cable TV applications.
The central wire also comes as a thick, single strand or as multiple strands. The latter is more flexible and can be bent, which means you should use a multi-strand wire cable if your CCTV application has pan and tilt functions. A cable with a single wire is perfect for a simple setup, but you cannot use it for pan and tilt applications as repeated bending can break the wire and affect the system.
The dielectric layer sits immediately outside the central wire and it improves the electric characteristics of the cable by making the parameters of capacitance, impedance, and attenuation more favourable for better signal propagation speed.
This means the signal travels more distance with greater strength and for optimum results should be made of polyethene or FEP (Fluorinated Ethylene Propylene).
The dielectric layer is covered in a braided sheath which is usually made of copper or aluminium strands. It has two functions, namely, to provide a grounding path that has low DC resistance, and act as a sheath to protect the cable from external interference.
The pure copper braided shield is best for CCTV as it can give a lower DC resistance path for grounding. Also, the covering provided by the braiding must be 95% or more to ensure the best shielding from interference caused by external signals.
Some cables have an additional aluminium foil covering as a layer inner to the braiding layer. It offers an even better shielding effect from RFI. However, more important is the quality and properties of the braiding material itself. In other words, the braiding must be of copper material and not aluminium for the best results.
Outer Insulating Jacket
The insulation layer or jacket is the outermost layer of the coaxial cable. Its main function is to cover all the inner layers and protect them from the environment and potentially destructive elements.
The jacket materials vary for indoor and outdoor installations. For outdoor applications, materials with high protective properties are used as they must withstand harsh weather, moisture, and other elements.
A plenum grade cable can be used inside ducts or plenums, whereas if the cable is designed to be exposed directly to rough weather and environmental conditions involving moisture, abrasion, heat, or sunlight, a polythene jacketed cable is recommended.
Every equipment connection has an impedance, and the cable used must also have a matching impedance value to reduce signal loss and obtain the maximum output. Usually, for CCTV equipment, the impedance value is 75 ohms, so you’ll need a cable that also has a 75-ohm impedance.
Otherwise, there will be a mismatch between the cable and the equipment, which will result in poor performance of your entire CCTV setup.
RG, or Radio Guide, classification is important when planning CCTV installation. The RG value represents the cables' attenuation range, that is, how far the signal can travel without weakening.
Most commonly, coaxial cables come in three different RG types – RG59, RG6, and RG11. You’ll get the least attenuation when you use RG11, where you can get the signal transmitted up to 2000 feet without disturbance.
If you use an RG6 cable, the attenuation will be a little higher, and the transmission distance is around 1500 feet. RG59 has the highest attenuation among the three types, whose transmission distance is around 750 feet.
Therefore, you need to select your cable based on the distance you need the signal to travel. However, in most cases, RG59 is adequate for offices, homes, flats, and other typical setups. The other two types are mostly used for special purposes and by government agencies or larger organisations.
It’s important to remember that the best cable alone cannot give you the best CCTV performance. The quality of other components including the camera, recording system, and connectors, are also important. Furthermore, having the right installation is also essential.