Hello. Want to follow and trace a paint-peeling leak mark in basement garage to the floor above this plinth, which is a passage near the bathroom. I suspect a galvanized steel (or copper) pipe has rotted from old age, and is buried somewhere under the floor. I want to build a coil or other antenna connected to an oscillator (modulated or tone), to penentrate about 2ft of concrete plinth. The oscillator / transmitting circuitry is no problem - I have books with dozens of osc/rf circuits. What I would like to find out is best frequency group (ELF / LF / MF ...) and which antenna or coil design would be directive at this short range (2ft>> TX-RX), allowing slight "spread" for detecting transmitter if off center. One person holds transmitter on mark at bottom, while other slowly sweeps across the floor in passage. When signal is loudest, floor is marked. Repeats process for rest of paint-mark (1 - 1.5 m). Avoids plumber having to lift all tiles and chop entire floor up to search bad spot. [hr] Would planar be the best send/search coil? As reading up on these animals, they apparently transmit perpendicular to the coil plane. As higher RF is attenuated by solid matter, should I go LF? I'm thinking maybe even 30-50Khz to create a pulsed tone. My books have various transmitter circuits incl LW/MW/SW/HF/VHF. What about 27MHz? ....Or is my logic too fuzzy? Regards, Fuzzy "Clive " Logic.