A Transceiver is a device that both transmits and receives; these properties are combined and share a single common circuit or a single housing. If no circuitry is common between the transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s. Technically, transceivers must combine a significant amount of the transmitter and receive handling circuitry. Similar devices include transponders, transverters and repeaters. In radio terminology, a transceiver means a unit which contains both a receiver and a transmitter. It was quite common to have these units separated. Ham radio operators can build their own equipment and it is always easier to design and build a simple unit having one of the functions, transmitting or receiving. Almost every modern piece of amateur radio equipment is now a transceiver, but there is still an active market for pure radio receivers, mainly shortwave listening operators. An example of this would be a walkie talkie, or a CB radio.