This apparatus consists of a self-contained transmitter and receiver operating in the 40 kHz region. The transmitted wave is modulated at a user controlled variable frequency of about 2 kHz and this is detected by the receiver which amplifies the signal and drives a miniature integral loudspeaker. Both transmitter and receiver are contained in separate plastic enclosures measuring 175 x 100 x 40 mm which contain all the electronics and the 9 V batteries. The receiver has front panel 4mm sockets so that the output can be monitored on an oscilloscope for more quantitative measurements. The system is ideal for demonstrating sound waves above the hearing threshold and reflection properties associated with sonar etc.

A special feature is the second transducer on the transmitter which can be switched on when required to produce two coherent sources. By moving the receiver along a line parallel to the two sources interference patterns can be dramatically demonstrated simplifying the Young’s slits experiment or enabling it to be demonstrated using waves other than light. Complete with batteries, full instructions and suggestions for use.