CLOSED-CIRCUIT TV
Closed-circuit TV (CCTV) is used primarily for surveillance. You have seen the small wall- or ceiling-mounted TV cameras in stores, airports, companies,
and today on the streets. The video signals are routed to a central point where multiple TV sets or monitors are set up for observation.
In many installations, the video is transmitted directly over coax cable to the monitors. There is no modulation involved. However, in some cases, when remote cameras are used, a wireless link via 2.4 GHz is typical. Of course, modulation is then used in the transmission so that a receiver is needed at the viewing end to recover the video.
Many installations also have video recorders (VHS tape or DVD) to capture several minutes or hours of video. In the past, most cameras were black and white, but today more and more use color.