CCTV (Closed Circuit Television) multiplexers are used in homes and businesses for video surveillance. CCTV cameras transfer their signals through a coaxial cable much like a cable TV cable. In cable TV applications each channel is transmitted through the cable on a different frequency. However, with CCTV cameras the signal being transmitted by each camera is the same frequency as all of the other cameras, so each camera must have a separate monitor. To reduce the cost of CCTV systems multiplexers were developed for use in CCTV systems so multiple cameras could be viewed on one monitor.
Since all CCTV cameras transmit their signals on one frequency there is no way to simply join all of the cables together into one cable and plug it into a monitor. Doing so would cause every signal to become un-viewable. Multiplexers use electronic circuitry to combine each individual signal into one signal which can be viewed on one monitor or recorded by one recording device such as a VCR.
CCTV multiplexers usually come in three sizes which are denoted in channels. According to CCTVMultiplexers.com there are typically 4, 9 and 16 channel units, and each channel connects to one camera; a 16 channel multiplexer can accommodate up to 16 CCTV cameras.
Installing a multiplexer is easy. Simply connect each camera to the multiplexer (sometimes called a mux) inputs and the output of the mux is connected to a monitor or recording device, and plug the multiplexer into a standard wall outlet.
Multiplexers typically have a few configuration settings. They can be configured to view one channel at a time or multiple channels simultaneously. Some multiplexers also have a setting called "dwell." Dwell allows the multiplexer to show each camera for a certain period of time (the dwell time) then the multiplexer will switch to the next camera. The multiplexer will continuously cycle through all of the cameras one-by-one. Some multiplexers also come with a remote to allow you to stop at a particular camera or change the multiplexer configuration.
Most modern security DVRs have multiplexers built into the DVR and therefore do not need an external multiplexer. Built-in multiplexers function just like external multiplexers and are incorporated seamlessly into the DVR operation.