Okay, what you want to do is go to your local Radio Shack or whatever you've got nearby, and ask for an
RF Modulator. If they ask you what kind of input you have, it's RCA. (That's the type of connector that those three plugs represent - yellow is the video, and red and white are the audio.)
The RF modulator should have a switch to select whether you want it to put the signal on channel 3 or 4.