RF modulator

An RF modulator (or radio frequency modulator) is an electronic device. Its input is a baseband signal. It is used to modulate a radio frequency source.
History.
Before the introduction of specialised video connector standards such as SCART, TVs were designed to only accept signals through the aerial connector. When equipment was developed which could use a television receiver as its display device, the signal was modulated and sent to the RF input connector.
RF modulators are now largely a third-party product. It is purchased primarily to run newer equipment such as DVD players with an old television set.
Design.
RF modulation puts the desired information on to a carrier signal at a standardized frequency. Amplitude or frequency modulation may be used, as required by the receiving equipment.
Even some units that have two or more audio inputs simply combine the left and right audio channels into one mono audio signal.
RF modulators produce a relatively poor picture. This is because the image quality is lost during both the modulation from the source device, and the demodulation in the television.
Uses.
Integrated modulators.
RF modulators are commonly integrated into VCRs and video game consoles up to the fourth generation, and in 8- and 16-bit home computers.
Broadcasting modulators.
RF modulators may also be used to take the audio and video signal from a PAL or NTSC composite video, RGB, YUV or other composite AV source. It also generate a broadcast RF signal that can be fed into a television's aerial/coaxial connector.