RF Demodulator - where to get one?

[Jeffrafa]

My friend and I are working on a science fair project and we are in need of a simple RF demodulator to go from a coaxial tv input to either a composite video line or preferrably RGB outputs. We need it to work primarily around channel 2 ( ~50 MHz input ) and we'd like it to be controlled by some sort of analog knob so that we can fine tune it into the frequency we need.

Does anyone know where we could get a demodulator like this for a reasonable price, or does anyone know how to make one that would do this for us?

Any help is greatly appreciated.

- Jeff