Abstract: A microprocessor based transmitter and a microprocessor based receiver in which a user interface is located on the receiver. The transmitter has an internal DC digital voltage measuring circuit to determine the voltage level of the battery powering the transmitter. Periodically, the transmitter's microprocessor inserts this digitally encoded voltage level in the sub-code area of the digital data being transmitted. The receiver decodes the DC voltage level of the transmitter battery, displays it, and inserts this voltage level in the sub-code area of its digital audio output signal. The voltage level of the transmitter battery is automatically recorded in the sub-code area of the DAT. By observing the DC voltage level, a trained operator can determine when the batteries are nearing the end of their useable life or that the battery voltage level is approaching its cut-off level.

Abstract: A transducer/transmitter captures not only the acoustic signal in the voice band, as in the prior art, but also an acoustic signal that includes audio signals outside the voice band; preferably above the voice band, up to approximately 20k Hertz. A band pass filter separates the transducer signal into two components; a voice signal with overlapping noise in the range of the human voice (e.g. from about 40 Hertz to 8k Hertz) and a component that provides a no voice signal, for example a signal in a no voice band extending from above approximately 8k Hertz to about 20k Hertz.