Phased-array Sonar for Rangefinding
David Gibson presents a computer-generated plot showing how the beam from a small ultrasonic transducer might be concentrated. (Front cover diagram).

UK VLF Licence Regulations
David Gibson summarises the MPT 1337 type-approval specification.

Optimal Design of a Cave Radio
David Gibson summarises some key points.

Lighting: The Aven Explorer
Small NiCd cells can be used with high wattage bulbs provided certain precautions are taken. David Gibson explains.

Cave Detection with rho, sigma, mu, epsilon. Part 1
David Gibson summarises the physical parameters that we could consider measuring in order to detect caves.

Are Q-Multipliers Any Use for Cave Radio
David Gibson questions the worth of the Q-multiplier, seen in several designs of cave radio receiver.