Abstract: A system and method communicate signals between a portable unit and a communications system. The portable device communicates with a base unit using inductive coupling. The base unit is further connected to a wider communication system such as a telephone network. Multiple, orthogonally arranged transducers are used in the base unit to provide a more complete magnetic field and to prevent mutual inductance nulls which are otherwise present in a magnetic field. The use of short-range inductive coupling minimizes the power requirements and limits interference with other sources. The inductive coupling may also be used to recharge a battery in the portable device.

Abstract: An overload protection circuit for a photomultiplier tube. A light source illuminates a photomultiplier tube which produces a signal proportional to the incoming radiation which is sent to photon counting electronics. The photon counting electronics produces a signal in proportion to the input photons to the photomultiplier tube and also provides an output to a frequency to voltage converter. The frequency to voltage converter is used to modulate a high voltage amplifier which controls the output of the photomultiplier tube. When the photon counting electronics indicate to the frequency to voltage converter that the photons produced by the photomultiplier tube exceed a predetermined maximum the high voltage amplifier reduces the gain of the photomultiplier tube. The gain of the photomultiplier tube is gradually reduced in proportion to the incident light level.