Generates the 40 KHz signal. 4mm sockets fitted on the panel of the unit. Generates the 40 KHz signal which is fed to the transducer cell and also to 4mm sockets 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. Unit Requires PP9 9 V battery (not supplied).