The Ultrasonic Transmitter generates the 40kHz signal which is fed to the transducer cell and also to 4mm sockets on the rear panel of the unit. This latter facility enables a second transducer to be driven simultaneously, providing an in-phase double point source for interference experiments, etc. Facilities are also provided for modulating the output of the transmitter using an audio signal generator or audio amplifier/microphone combination. By this method the transmission of speech or other audio information is possible over a distance in excess of 100m. Casing Dimensions: 150mm x 95mm x 60mm,. Horn Dimensions (mouth diam. x length): 75mm x 100mm. Requires PP9 9V battery (not supplied).