Abstract: The detection and indication of volleyball out of bounds occurrences is realized by means of a light beam type system that distinguishes between the volleyball and other beam disrupting agents. Two juxtaposed light beams, one over the other, and separated by a distance equal to 1.5 volleyball diameters are projected along and 0.5 volleyball diameters outside of the sideline and endline bounds of the volleyball court. The beams are separately monitored by detectors that respond to beam interruptions. The lower beam is spaced from the playing surface by about three inches. Visual out of bounds indicators are actuated by a control circuit that responds exclusively to lower beam interruptions.

Abstract: Volleyball net touch violations are detected and an indicator identifying the offending team is actuated by a system that incorporates antennas into the volleyball net and utilizes radiant energy generated by court illuminating lights. A wire mesh antenna is affixed to each side of the net. The outputs of the antennas are amplified and compared with a reference. A player touching either net adds capacitance to the system producing a measurable signal. A NAND gate logic circuit determines which net was touched and actuates the appropriate indicator. The system does not respond to the volleyball which is a dielectric material does not add capacitance to the system.

Abstract: An oscillator generates a fixed frequency ultrasonic output signal. After wer amplification this signal drives a transmitting transducer which projects an ultrasonic beam into water. Reflected signals are received by a receiving transducer and AGC preamplified. A chopper multiplies the received signal with the transmitted signal and generates an output signal if a target exists. To determine whether the target is a swimmer, this output signal is band pass filtered and amplified and then fed both to an automatic alarm and to a set of headphones. A human operator listening to the headphone output classifies the target and determines exact bearing.

Abstract: An underwater intrusion alarm system using an array of one or more remotely eployable, acoustic doppler detector probes. Each probe is a unitary submersible buoy formed by a pair of vertically coaxially and acoustically isolated, right cylindrical active transducer elements that are shielded from surface and bottom reflections. Transmitter and receiver circuits may be located either in the buoy with an external connection to conveniently located headphones and alarms or at a distant site with a fixed wire connection to the buoy transducer elements. A depth sensitive ancilliary mechanism regulates the submergence of the buoy in conformance with the rise and fall of the tide.