The function of an RF modulator is simple. The RF modulator converts the video (and/or audio) output of a DVD player (or camcorder or video game) into a channel 3/4 signal that is compatible with a TV's cable or antenna input.
There are many RF modulators available, but all function in a similar fashion. The main feature of an RF modulator is that makes it perfectly suited for use with DVD is the capacity for it to accept the standard audio/video outputs of a DVD player and the cable input (even passed through a VCR) simultaneously.
Setting up an RF modulator is fairly straightforward:
First: Plug your Cable TV/VCR output into the Cable input connection of the RF modulator and the DVD player into the RF modulator's AV (Red, White, and Yellow OR Red, White, and S-Video) inputs.
Second: Connect a standard RF cable from the RF modulator to your TV.
Third: Select either the channel 3 or 4 output on the back of the RF modulator.
Fourth: Turn the TV on and the RF modulator will automatically detect your cable input for the TV. When you want to watch your DVD player, just put the TV on channel 3 or 4, turn the DVD player on and the RF modulator will automatically detect the DVD player and will display your movie. When you turn the DVD player off, the RF Modulator should revert back to normal TV viewing.
For a visual presentation of also the above procedures, also check out my Step-By-Step on connecting and using an RF Modulator.