With ring modulation, the amplitude of a carrier signal is changed by the amplitude of the modulator signal so that the two signals are actually MULTIPLIED together. This produces sideband frequencies that are the sum and difference of the frequencies present in the two signals.
I'm pretty sure I used the simple circuit below to construct this, found on the web somewhere. I can't remember exactly, as it's been a while.
This link has some good info: http://www.asciipr0n.com/4096/ringmod/