RF Locator

My knowledge of RF techniques is somewhat lacking, but have recently become intrigued, especially about its propagation properties.

I would like to start a project to help me understand more. It is simply a locator which could find a buried transmitter by strength of signal.

Any ideas to get me started, like what frequencies, power/type of transmitters i should be considering. How could i 'measure' the strength of the signal? etc.

Regards,
Chris