CCTV background
Analogue Closed Circuit Television (CCTV) was invented during the Second World War by the German government of the time as part of their V2 military rocket research. The cameras were mounted in such a way as to allow live remote monitoring of test rocket launches from a safe position.
The technology was developed further after the war by UK electronics company PYE and also Radio Corporation of America (RCA). CCTV systems were used extensively in the US missile and space programs.
However the use of CCTV didn’t really ‘take off’ at a consumer level until the invention of the Video Cassette Recorder (VCR) in the 1970s.
In the early days of analogue CCTV, coaxial cables were used to transport the analogue video signal, with each end terminated according to that manufacturer’s own specifications. Later the industry standardised on PL-259 Coaxial plug /socket, but this eventually changed to the Bayonet Neill–Concelman (BNC) plug / socket type, as they were much smaller and allowed cameras to be connected to the equipment in a more densely packed manner.
CCTV systems mainly (but not exclusively) use coaxial cable links from each camera back to the recording device, nowadays terminated with BNC plugs. Within a typical building these coax cables would usually be of RG-59 or URM-70 type, which provides an acceptable signal for up to 300ft (288 metres). Power for each camera can be centralised or distributed depending on the site.
The picture from the camera is supplied over a 1 volt peak to peak composite video signal, which travels along the centre core of the coax cable. Composite video is also known by the initials CVBS for composite video baseband signal or colour, video, blanking and sync, or is simply referred to as SD video for the standard-definition television signal it conveys. There are three dominant variants of composite video: NTSC, PAL, and SECAM. The outer cable screen provides a ground reference, which can sometimes prove to be problematic due to ground loops.
The recorder end of the cable must be correctly terminated at 75 ohms to ensure a good quality picture. failure to do this properly can cause double images, whiteout images or blackout images. Modern recorders handle this detail automatically.
Digital CCTV
Due to the advent of Digital Television in the UK (2008-onwards) and elsewhere which provide 'High Definition' (HD) and 'Ultra High Definition' (UHD) images, CCTV systems have evolved to make use of the prevailing television technology, as demanded by the customer. Modern Digital CCTV can provide High Definition or Ultra High Definition images over legacy analogue CCTV coaxial cables. However these signals are incompatible with legacy analogue CCTV recorders. Digital CCTV systems have now taken over from analogue CCTV, and you will find it difficult to get spares for old analogue systems.
Digital CCTV is a direct competitor in the marketplace to IP-based Digital Video Systems (also known as IP CCTV).
CCTV systems installed in the UK should conform to BS EN 50132, which specifies standards for design and installation.